From: Roberto Sassu roberto.sassu@huawei.com
include/linux/lsm_hooks.h reports the result of the LSM infrastructure to the callers, not what LSMs should return to the LSM infrastructure.
Clarify that and add that returning 1 from the LSMs means calling __vm_enough_memory() with cap_sys_admin set, 0 without.
Signed-off-by: Roberto Sassu roberto.sassu@huawei.com --- include/linux/lsm_hooks.h | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h index 4ec80b96c22e..f40b82ca91e7 100644 --- a/include/linux/lsm_hooks.h +++ b/include/linux/lsm_hooks.h @@ -1411,7 +1411,9 @@ * Check permissions for allocating a new virtual mapping. * @mm contains the mm struct it is being added to. * @pages contains the number of pages. - * Return 0 if permission is granted. + * Return 0 if permission is granted by LSMs to the caller. LSMs should + * return 1 if __vm_enough_memory() should be called with + * cap_sys_admin set, 0 if not. * * @ismaclabel: * Check if the extended attribute specified by @name
From: Roberto Sassu roberto.sassu@huawei.com
BPF LSM defines a bpf_lsm_*() function for each LSM hook, so that security modules can define their own implementation for the desired hooks.
Unfortunately, BPF LSM does not restrict which values security modules can return (for non-void LSM hooks). Security modules might follow the conventions stated in include/linux/lsm_hooks.h, or put arbitrary values.
This could cause big troubles, as the kernel is not ready to handle possibly malicious return values from LSMs. Until now, it was not the case, as each LSM is carefully reviewed and it won't be accepted if it does not meet the return value conventions.
The biggest problem is when an LSM returns a positive value, instead of a negative value, as it could be converted to a pointer. Since such pointer escapes the IS_ERR() check, its use later in the code can cause unpredictable consequences (e.g. invalid memory access).
Another problem is returning zero when an LSM is supposed to have done some operations. For example, the inode_init_security hook expects that their implementations return zero only if they set the name and value of the new xattr to be added to the new inode. Otherwise, other kernel subsystems might encounter unexpected conditions leading to a crash (e.g. evm_protected_xattr_common() getting NULL as argument).
Finally, there are LSM hooks which are supposed to return just one as positive value, or non-negative values. Also in these cases, although it seems less critical, it is safer to return to callers of the LSM infrastructure more precisely what they expect.
As eBPF allows code outside the kernel to run, it is its responsibility to ensure that only expected values are returned to LSM infrastructure callers.
Create four new BTF ID sets, respectively for hooks that can return positive values, only one as positive value, that cannot return zero, and that cannot return negative values. Create also corresponding functions to check if the hook a security module is attached to belongs to one of the defined sets.
Finally, check in the eBPF verifier the value returned by security modules for each attached LSM hook, and return -EINVAL (the security module cannot run) if the hook implementation does not satisfy the hook return value policy.
Cc: stable@vger.kernel.org Fixes: 9d3fdea789c8 ("bpf: lsm: Provide attachment points for BPF LSM programs") Signed-off-by: Roberto Sassu roberto.sassu@huawei.com --- include/linux/bpf_lsm.h | 24 ++++++++++++++++++ kernel/bpf/bpf_lsm.c | 56 +++++++++++++++++++++++++++++++++++++++++ kernel/bpf/verifier.c | 35 +++++++++++++++++++++++--- 3 files changed, 112 insertions(+), 3 deletions(-)
diff --git a/include/linux/bpf_lsm.h b/include/linux/bpf_lsm.h index 4bcf76a9bb06..cd38aca4cfc0 100644 --- a/include/linux/bpf_lsm.h +++ b/include/linux/bpf_lsm.h @@ -28,6 +28,10 @@ int bpf_lsm_verify_prog(struct bpf_verifier_log *vlog, const struct bpf_prog *prog);
bool bpf_lsm_is_sleepable_hook(u32 btf_id); +bool bpf_lsm_can_ret_pos_value(u32 btf_id); +bool bpf_lsm_can_ret_only_one_as_pos_value(u32 btf_id); +bool bpf_lsm_cannot_ret_zero(u32 btf_id); +bool bpf_lsm_cannot_ret_neg_value(u32 btf_id);
static inline struct bpf_storage_blob *bpf_inode( const struct inode *inode) @@ -51,6 +55,26 @@ static inline bool bpf_lsm_is_sleepable_hook(u32 btf_id) return false; }
+static inline bool bpf_lsm_can_ret_pos_value(u32 btf_id) +{ + return false; +} + +static inline bool bpf_lsm_can_ret_only_one_as_pos_value(u32 btf_id) +{ + return false; +} + +static inline bool bpf_lsm_cannot_ret_zero(u32 btf_id) +{ + return false; +} + +static inline bool bpf_lsm_cannot_ret_neg_value(u32 btf_id) +{ + return false; +} + static inline int bpf_lsm_verify_prog(struct bpf_verifier_log *vlog, const struct bpf_prog *prog) { diff --git a/kernel/bpf/bpf_lsm.c b/kernel/bpf/bpf_lsm.c index d6c9b3705f24..3dcb70b2f978 100644 --- a/kernel/bpf/bpf_lsm.c +++ b/kernel/bpf/bpf_lsm.c @@ -348,6 +348,62 @@ bool bpf_lsm_is_sleepable_hook(u32 btf_id) return btf_id_set_contains(&sleepable_lsm_hooks, btf_id); }
+/* The set of hooks which are allowed to return a positive value. */ +BTF_SET_START(pos_ret_value_lsm_hooks) +BTF_ID(func, bpf_lsm_vm_enough_memory) +BTF_ID(func, bpf_lsm_inode_getsecurity) +BTF_ID(func, bpf_lsm_inode_listsecurity) +BTF_ID(func, bpf_lsm_inode_need_killpriv) +BTF_ID(func, bpf_lsm_inode_copy_up_xattr) +BTF_ID(func, bpf_lsm_getprocattr) +BTF_ID(func, bpf_lsm_setprocattr) +BTF_ID(func, bpf_lsm_xfrm_state_pol_flow_match) +BTF_ID(func, bpf_lsm_key_getsecurity) +BTF_ID(func, bpf_lsm_ismaclabel) +BTF_ID(func, bpf_lsm_audit_rule_known) +BTF_ID(func, bpf_lsm_audit_rule_match) +BTF_SET_END(pos_ret_value_lsm_hooks) + +bool bpf_lsm_can_ret_pos_value(u32 btf_id) +{ + return btf_id_set_contains(&pos_ret_value_lsm_hooks, btf_id); +} + +BTF_SET_START(one_ret_value_lsm_hooks) +BTF_ID(func, bpf_lsm_vm_enough_memory) +BTF_ID(func, bpf_lsm_inode_copy_up_xattr) +BTF_ID(func, bpf_lsm_xfrm_state_pol_flow_match) +BTF_ID(func, bpf_lsm_ismaclabel) +BTF_ID(func, bpf_lsm_audit_rule_known) +BTF_ID(func, bpf_lsm_audit_rule_match) +BTF_SET_END(one_ret_value_lsm_hooks) + +bool bpf_lsm_can_ret_only_one_as_pos_value(u32 btf_id) +{ + return btf_id_set_contains(&one_ret_value_lsm_hooks, btf_id); +} + +/* The set of hooks which are not allowed to return zero. */ +BTF_SET_START(not_zero_ret_value_lsm_hooks) +BTF_ID(func, bpf_lsm_inode_init_security) +BTF_SET_END(not_zero_ret_value_lsm_hooks) + +bool bpf_lsm_cannot_ret_zero(u32 btf_id) +{ + return btf_id_set_contains(¬_zero_ret_value_lsm_hooks, btf_id); +} + +/* The set of hooks which are not allowed to return a negative value. */ +BTF_SET_START(not_neg_ret_value_lsm_hooks) +BTF_ID(func, bpf_lsm_vm_enough_memory) +BTF_ID(func, bpf_lsm_audit_rule_known) +BTF_SET_END(not_neg_ret_value_lsm_hooks) + +bool bpf_lsm_cannot_ret_neg_value(u32 btf_id) +{ + return btf_id_set_contains(¬_neg_ret_value_lsm_hooks, btf_id); +} + const struct bpf_prog_ops lsm_prog_ops = { };
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 7f0a9f6cb889..099c1bf88fed 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -10623,9 +10623,38 @@ static int check_return_code(struct bpf_verifier_env *env)
case BPF_PROG_TYPE_LSM: if (env->prog->expected_attach_type != BPF_LSM_CGROUP) { - /* Regular BPF_PROG_TYPE_LSM programs can return - * any value. - */ + /* < 0 */ + if (tnum_in(tnum_range((u64)(~0) << 31, (u64)(~0)), reg->var_off)) { + if (bpf_lsm_cannot_ret_neg_value(env->prog->aux->attach_btf_id)) { + verbose(env, "Invalid R0, cannot return negative value\n"); + return -EINVAL; + } + /* = 0 */ + } else if (tnum_equals_const(reg->var_off, 0)) { + if (bpf_lsm_cannot_ret_zero(env->prog->aux->attach_btf_id)) { + verbose(env, "Invalid R0, cannot return zero value\n"); + return -EINVAL; + } + /* = 1 */ + } else if (tnum_equals_const(reg->var_off, 1)) { + if (!bpf_lsm_can_ret_pos_value(env->prog->aux->attach_btf_id)) { + verbose(env, "Invalid R0, cannot return positive value\n"); + return -EINVAL; + } + /* > 1 */ + } else { + if (!bpf_lsm_can_ret_pos_value(env->prog->aux->attach_btf_id)) { + verbose(env, "Invalid R0, cannot return positive value\n"); + return -EINVAL; + } + + if (bpf_lsm_can_ret_only_one_as_pos_value(env->prog->aux->attach_btf_id)) { + verbose(env, + "Invalid R0, can return only one as positive value\n"); + return -EINVAL; + } + } + return 0; } if (!env->prog->aux->attach_func_proto->type) {
On Fri, Oct 28, 2022 at 6:55 PM Roberto Sassu roberto.sassu@huaweicloud.com wrote:
From: Roberto Sassu roberto.sassu@huawei.com
BPF LSM defines a bpf_lsm_*() function for each LSM hook, so that security modules can define their own implementation for the desired hooks.
Unfortunately, BPF LSM does not restrict which values security modules can return (for non-void LSM hooks). Security modules might follow the conventions stated in include/linux/lsm_hooks.h, or put arbitrary values.
This could cause big troubles, as the kernel is not ready to handle possibly malicious return values from LSMs. Until now, it was not the
I am not sure I would call this malicious. This would be incorrect, if someone is writing a BPF LSM program they already have the powers to willingly do a lot of malicious stuff.
It's about unknowingly returning values that can break the system.
case, as each LSM is carefully reviewed and it won't be accepted if it does not meet the return value conventions.
The biggest problem is when an LSM returns a positive value, instead of a negative value, as it could be converted to a pointer. Since such pointer escapes the IS_ERR() check, its use later in the code can cause unpredictable consequences (e.g. invalid memory access).
Another problem is returning zero when an LSM is supposed to have done some operations. For example, the inode_init_security hook expects that their implementations return zero only if they set the name and value of the new xattr to be added to the new inode. Otherwise, other kernel subsystems might encounter unexpected conditions leading to a crash (e.g. evm_protected_xattr_common() getting NULL as argument).
Finally, there are LSM hooks which are supposed to return just one as positive value, or non-negative values. Also in these cases, although it seems less critical, it is safer to return to callers of the LSM infrastructure more precisely what they expect.
As eBPF allows code outside the kernel to run, it is its responsibility to ensure that only expected values are returned to LSM infrastructure callers.
Create four new BTF ID sets, respectively for hooks that can return positive values, only one as positive value, that cannot return zero, and that cannot return negative values. Create also corresponding functions to check if the hook a security module is attached to belongs to one of the defined sets.
Finally, check in the eBPF verifier the value returned by security modules for each attached LSM hook, and return -EINVAL (the security module cannot run) if the hook implementation does not satisfy the hook return value policy.
Cc: stable@vger.kernel.org Fixes: 9d3fdea789c8 ("bpf: lsm: Provide attachment points for BPF LSM programs") Signed-off-by: Roberto Sassu roberto.sassu@huawei.com
include/linux/bpf_lsm.h | 24 ++++++++++++++++++ kernel/bpf/bpf_lsm.c | 56 +++++++++++++++++++++++++++++++++++++++++ kernel/bpf/verifier.c | 35 +++++++++++++++++++++++--- 3 files changed, 112 insertions(+), 3 deletions(-)
diff --git a/include/linux/bpf_lsm.h b/include/linux/bpf_lsm.h index 4bcf76a9bb06..cd38aca4cfc0 100644 --- a/include/linux/bpf_lsm.h +++ b/include/linux/bpf_lsm.h @@ -28,6 +28,10 @@ int bpf_lsm_verify_prog(struct bpf_verifier_log *vlog, const struct bpf_prog *prog);
bool bpf_lsm_is_sleepable_hook(u32 btf_id); +bool bpf_lsm_can_ret_pos_value(u32 btf_id); +bool bpf_lsm_can_ret_only_one_as_pos_value(u32 btf_id); +bool bpf_lsm_cannot_ret_zero(u32 btf_id); +bool bpf_lsm_cannot_ret_neg_value(u32 btf_id);
This does not need to be exported to the rest of the kernel. Please have this logic in bpf_lsm.c and export a single verify function.
Also, these really don't need to be such scattered logic, Could we somehow encode this into the LSM_HOOK definition?
static inline struct bpf_storage_blob *bpf_inode( const struct inode *inode) @@ -51,6 +55,26 @@ static inline bool bpf_lsm_is_sleepable_hook(u32 btf_id) return false; }
+static inline bool bpf_lsm_can_ret_pos_value(u32 btf_id) +{
return false;+}
+static inline bool bpf_lsm_can_ret_only_one_as_pos_value(u32 btf_id) +{
return false;+}
+static inline bool bpf_lsm_cannot_ret_zero(u32 btf_id) +{
return false;+}
+static inline bool bpf_lsm_cannot_ret_neg_value(u32 btf_id) +{
return false;+}
static inline int bpf_lsm_verify_prog(struct bpf_verifier_log *vlog, const struct bpf_prog *prog) { diff --git a/kernel/bpf/bpf_lsm.c b/kernel/bpf/bpf_lsm.c index d6c9b3705f24..3dcb70b2f978 100644 --- a/kernel/bpf/bpf_lsm.c +++ b/kernel/bpf/bpf_lsm.c @@ -348,6 +348,62 @@ bool bpf_lsm_is_sleepable_hook(u32 btf_id) return btf_id_set_contains(&sleepable_lsm_hooks, btf_id); }
+/* The set of hooks which are allowed to return a positive value. */ +BTF_SET_START(pos_ret_value_lsm_hooks) +BTF_ID(func, bpf_lsm_vm_enough_memory) +BTF_ID(func, bpf_lsm_inode_getsecurity) +BTF_ID(func, bpf_lsm_inode_listsecurity) +BTF_ID(func, bpf_lsm_inode_need_killpriv) +BTF_ID(func, bpf_lsm_inode_copy_up_xattr) +BTF_ID(func, bpf_lsm_getprocattr) +BTF_ID(func, bpf_lsm_setprocattr) +BTF_ID(func, bpf_lsm_xfrm_state_pol_flow_match) +BTF_ID(func, bpf_lsm_key_getsecurity) +BTF_ID(func, bpf_lsm_ismaclabel) +BTF_ID(func, bpf_lsm_audit_rule_known) +BTF_ID(func, bpf_lsm_audit_rule_match) +BTF_SET_END(pos_ret_value_lsm_hooks)
+bool bpf_lsm_can_ret_pos_value(u32 btf_id) +{
return btf_id_set_contains(&pos_ret_value_lsm_hooks, btf_id);+}
+BTF_SET_START(one_ret_value_lsm_hooks) +BTF_ID(func, bpf_lsm_vm_enough_memory) +BTF_ID(func, bpf_lsm_inode_copy_up_xattr) +BTF_ID(func, bpf_lsm_xfrm_state_pol_flow_match) +BTF_ID(func, bpf_lsm_ismaclabel) +BTF_ID(func, bpf_lsm_audit_rule_known) +BTF_ID(func, bpf_lsm_audit_rule_match) +BTF_SET_END(one_ret_value_lsm_hooks)
+bool bpf_lsm_can_ret_only_one_as_pos_value(u32 btf_id) +{
return btf_id_set_contains(&one_ret_value_lsm_hooks, btf_id);+}
+/* The set of hooks which are not allowed to return zero. */ +BTF_SET_START(not_zero_ret_value_lsm_hooks) +BTF_ID(func, bpf_lsm_inode_init_security) +BTF_SET_END(not_zero_ret_value_lsm_hooks)
+bool bpf_lsm_cannot_ret_zero(u32 btf_id) +{
return btf_id_set_contains(¬_zero_ret_value_lsm_hooks, btf_id);+}
+/* The set of hooks which are not allowed to return a negative value. */ +BTF_SET_START(not_neg_ret_value_lsm_hooks) +BTF_ID(func, bpf_lsm_vm_enough_memory) +BTF_ID(func, bpf_lsm_audit_rule_known) +BTF_SET_END(not_neg_ret_value_lsm_hooks)
+bool bpf_lsm_cannot_ret_neg_value(u32 btf_id) +{
return btf_id_set_contains(¬_neg_ret_value_lsm_hooks, btf_id);+}
const struct bpf_prog_ops lsm_prog_ops = { };
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 7f0a9f6cb889..099c1bf88fed 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -10623,9 +10623,38 @@ static int check_return_code(struct bpf_verifier_env *env)
case BPF_PROG_TYPE_LSM: if (env->prog->expected_attach_type != BPF_LSM_CGROUP) {
/* Regular BPF_PROG_TYPE_LSM programs can return* any value.*/
/* < 0 */if (tnum_in(tnum_range((u64)(~0) << 31, (u64)(~0)), reg->var_off)) {if (bpf_lsm_cannot_ret_neg_value(env->prog->aux->attach_btf_id)) {verbose(env, "Invalid R0, cannot return negative value\n");return -EINVAL;}/* = 0 */} else if (tnum_equals_const(reg->var_off, 0)) {if (bpf_lsm_cannot_ret_zero(env->prog->aux->attach_btf_id)) {verbose(env, "Invalid R0, cannot return zero value\n");return -EINVAL;}/* = 1 */} else if (tnum_equals_const(reg->var_off, 1)) {if (!bpf_lsm_can_ret_pos_value(env->prog->aux->attach_btf_id)) {verbose(env, "Invalid R0, cannot return positive value\n");return -EINVAL;}/* > 1 */} else {if (!bpf_lsm_can_ret_pos_value(env->prog->aux->attach_btf_id)) {verbose(env, "Invalid R0, cannot return positive value\n");return -EINVAL;}if (bpf_lsm_can_ret_only_one_as_pos_value(env->prog->aux->attach_btf_id)) {verbose(env,"Invalid R0, can return only one as positive value\n");return -EINVAL;}}return 0; } if (!env->prog->aux->attach_func_proto->type) {-- 2.25.1
On Thu, 2022-11-03 at 16:09 +0100, KP Singh wrote:
On Fri, Oct 28, 2022 at 6:55 PM Roberto Sassu roberto.sassu@huaweicloud.com wrote:
From: Roberto Sassu roberto.sassu@huawei.com
BPF LSM defines a bpf_lsm_*() function for each LSM hook, so that security modules can define their own implementation for the desired hooks.
Unfortunately, BPF LSM does not restrict which values security modules can return (for non-void LSM hooks). Security modules might follow the conventions stated in include/linux/lsm_hooks.h, or put arbitrary values.
This could cause big troubles, as the kernel is not ready to handle possibly malicious return values from LSMs. Until now, it was not the
I am not sure I would call this malicious. This would be incorrect, if someone is writing a BPF LSM program they already have the powers to willingly do a lot of malicious stuff.
It's about unknowingly returning values that can break the system.
Maybe it is possible to return specific values that lead to acquire more information/do actions that the eBPF program is not supposed to cause.
I don't have a concrete example, so I will use the word you suggested.
case, as each LSM is carefully reviewed and it won't be accepted if it does not meet the return value conventions.
The biggest problem is when an LSM returns a positive value, instead of a negative value, as it could be converted to a pointer. Since such pointer escapes the IS_ERR() check, its use later in the code can cause unpredictable consequences (e.g. invalid memory access).
Another problem is returning zero when an LSM is supposed to have done some operations. For example, the inode_init_security hook expects that their implementations return zero only if they set the name and value of the new xattr to be added to the new inode. Otherwise, other kernel subsystems might encounter unexpected conditions leading to a crash (e.g. evm_protected_xattr_common() getting NULL as argument).
Finally, there are LSM hooks which are supposed to return just one as positive value, or non-negative values. Also in these cases, although it seems less critical, it is safer to return to callers of the LSM infrastructure more precisely what they expect.
As eBPF allows code outside the kernel to run, it is its responsibility to ensure that only expected values are returned to LSM infrastructure callers.
Create four new BTF ID sets, respectively for hooks that can return positive values, only one as positive value, that cannot return zero, and that cannot return negative values. Create also corresponding functions to check if the hook a security module is attached to belongs to one of the defined sets.
Finally, check in the eBPF verifier the value returned by security modules for each attached LSM hook, and return -EINVAL (the security module cannot run) if the hook implementation does not satisfy the hook return value policy.
Cc: stable@vger.kernel.org Fixes: 9d3fdea789c8 ("bpf: lsm: Provide attachment points for BPF LSM programs") Signed-off-by: Roberto Sassu roberto.sassu@huawei.com
include/linux/bpf_lsm.h | 24 ++++++++++++++++++ kernel/bpf/bpf_lsm.c | 56 +++++++++++++++++++++++++++++++++++++++++ kernel/bpf/verifier.c | 35 +++++++++++++++++++++++--- 3 files changed, 112 insertions(+), 3 deletions(-)
diff --git a/include/linux/bpf_lsm.h b/include/linux/bpf_lsm.h index 4bcf76a9bb06..cd38aca4cfc0 100644 --- a/include/linux/bpf_lsm.h +++ b/include/linux/bpf_lsm.h @@ -28,6 +28,10 @@ int bpf_lsm_verify_prog(struct bpf_verifier_log *vlog, const struct bpf_prog *prog);
bool bpf_lsm_is_sleepable_hook(u32 btf_id); +bool bpf_lsm_can_ret_pos_value(u32 btf_id); +bool bpf_lsm_can_ret_only_one_as_pos_value(u32 btf_id); +bool bpf_lsm_cannot_ret_zero(u32 btf_id); +bool bpf_lsm_cannot_ret_neg_value(u32 btf_id);
This does not need to be exported to the rest of the kernel. Please have this logic in bpf_lsm.c and export a single verify function.
Also, these really don't need to be such scattered logic, Could we somehow encode this into the LSM_HOOK definition?
The problem is that a new LSM_HOOK definition would apply to every LSM hook, while we need the ability to select subsets.
I was thinking, but I didn't check yet, what about using BTF_ID_FLAGS, introducing a flag for each interval (<0, 0, 1, >1) and setting the appropriate flags for each LSM hook?
Roberto
static inline struct bpf_storage_blob *bpf_inode( const struct inode *inode) @@ -51,6 +55,26 @@ static inline bool bpf_lsm_is_sleepable_hook(u32 btf_id) return false; }
+static inline bool bpf_lsm_can_ret_pos_value(u32 btf_id) +{
return false;+}
+static inline bool bpf_lsm_can_ret_only_one_as_pos_value(u32 btf_id) +{
return false;+}
+static inline bool bpf_lsm_cannot_ret_zero(u32 btf_id) +{
return false;+}
+static inline bool bpf_lsm_cannot_ret_neg_value(u32 btf_id) +{
return false;+}
static inline int bpf_lsm_verify_prog(struct bpf_verifier_log *vlog, const struct bpf_prog *prog) { diff --git a/kernel/bpf/bpf_lsm.c b/kernel/bpf/bpf_lsm.c index d6c9b3705f24..3dcb70b2f978 100644 --- a/kernel/bpf/bpf_lsm.c +++ b/kernel/bpf/bpf_lsm.c @@ -348,6 +348,62 @@ bool bpf_lsm_is_sleepable_hook(u32 btf_id) return btf_id_set_contains(&sleepable_lsm_hooks, btf_id); }
+/* The set of hooks which are allowed to return a positive value. */ +BTF_SET_START(pos_ret_value_lsm_hooks) +BTF_ID(func, bpf_lsm_vm_enough_memory) +BTF_ID(func, bpf_lsm_inode_getsecurity) +BTF_ID(func, bpf_lsm_inode_listsecurity) +BTF_ID(func, bpf_lsm_inode_need_killpriv) +BTF_ID(func, bpf_lsm_inode_copy_up_xattr) +BTF_ID(func, bpf_lsm_getprocattr) +BTF_ID(func, bpf_lsm_setprocattr) +BTF_ID(func, bpf_lsm_xfrm_state_pol_flow_match) +BTF_ID(func, bpf_lsm_key_getsecurity) +BTF_ID(func, bpf_lsm_ismaclabel) +BTF_ID(func, bpf_lsm_audit_rule_known) +BTF_ID(func, bpf_lsm_audit_rule_match) +BTF_SET_END(pos_ret_value_lsm_hooks)
+bool bpf_lsm_can_ret_pos_value(u32 btf_id) +{
return btf_id_set_contains(&pos_ret_value_lsm_hooks, btf_id);+}
+BTF_SET_START(one_ret_value_lsm_hooks) +BTF_ID(func, bpf_lsm_vm_enough_memory) +BTF_ID(func, bpf_lsm_inode_copy_up_xattr) +BTF_ID(func, bpf_lsm_xfrm_state_pol_flow_match) +BTF_ID(func, bpf_lsm_ismaclabel) +BTF_ID(func, bpf_lsm_audit_rule_known) +BTF_ID(func, bpf_lsm_audit_rule_match) +BTF_SET_END(one_ret_value_lsm_hooks)
+bool bpf_lsm_can_ret_only_one_as_pos_value(u32 btf_id) +{
return btf_id_set_contains(&one_ret_value_lsm_hooks, btf_id);+}
+/* The set of hooks which are not allowed to return zero. */ +BTF_SET_START(not_zero_ret_value_lsm_hooks) +BTF_ID(func, bpf_lsm_inode_init_security) +BTF_SET_END(not_zero_ret_value_lsm_hooks)
+bool bpf_lsm_cannot_ret_zero(u32 btf_id) +{
return btf_id_set_contains(¬_zero_ret_value_lsm_hooks, btf_id);+}
+/* The set of hooks which are not allowed to return a negative value. */ +BTF_SET_START(not_neg_ret_value_lsm_hooks) +BTF_ID(func, bpf_lsm_vm_enough_memory) +BTF_ID(func, bpf_lsm_audit_rule_known) +BTF_SET_END(not_neg_ret_value_lsm_hooks)
+bool bpf_lsm_cannot_ret_neg_value(u32 btf_id) +{
return btf_id_set_contains(¬_neg_ret_value_lsm_hooks, btf_id);+}
const struct bpf_prog_ops lsm_prog_ops = { };
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 7f0a9f6cb889..099c1bf88fed 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -10623,9 +10623,38 @@ static int check_return_code(struct bpf_verifier_env *env)
case BPF_PROG_TYPE_LSM: if (env->prog->expected_attach_type != BPF_LSM_CGROUP) {
/* Regular BPF_PROG_TYPE_LSM programs can return* any value.*/
/* < 0 */if (tnum_in(tnum_range((u64)(~0) << 31, (u64)(~0)), reg->var_off)) {if (bpf_lsm_cannot_ret_neg_value(env->prog->aux->attach_btf_id)) {verbose(env, "Invalid R0, cannot return negative value\n");return -EINVAL;}/* = 0 */} else if (tnum_equals_const(reg->var_off, 0)) {if (bpf_lsm_cannot_ret_zero(env->prog->aux->attach_btf_id)) {verbose(env, "Invalid R0, cannot return zero value\n");return -EINVAL;}/* = 1 */} else if (tnum_equals_const(reg->var_off, 1)) {if (!bpf_lsm_can_ret_pos_value(env->prog->aux->attach_btf_id)) {verbose(env, "Invalid R0, cannot return positive value\n");return -EINVAL;}/* > 1 */} else {if (!bpf_lsm_can_ret_pos_value(env->prog->aux->attach_btf_id)) {verbose(env, "Invalid R0, cannot return positive value\n");return -EINVAL;}if (bpf_lsm_can_ret_only_one_as_pos_value(env->prog->aux->attach_btf_id)) {verbose(env,"Invalid R0, can return only one as positive value\n");return -EINVAL;}}return 0; } if (!env->prog->aux->attach_func_proto->type) {-- 2.25.1
On Fri, Nov 4, 2022 at 8:29 AM Roberto Sassu roberto.sassu@huaweicloud.com wrote:
On Thu, 2022-11-03 at 16:09 +0100, KP Singh wrote:
On Fri, Oct 28, 2022 at 6:55 PM Roberto Sassu roberto.sassu@huaweicloud.com wrote:
From: Roberto Sassu roberto.sassu@huawei.com
BPF LSM defines a bpf_lsm_*() function for each LSM hook, so that security modules can define their own implementation for the desired hooks.
Unfortunately, BPF LSM does not restrict which values security modules can return (for non-void LSM hooks). Security modules might follow the conventions stated in include/linux/lsm_hooks.h, or put arbitrary values.
This could cause big troubles, as the kernel is not ready to handle possibly malicious return values from LSMs. Until now, it was not the
I am not sure I would call this malicious. This would be incorrect, if someone is writing a BPF LSM program they already have the powers to willingly do a lot of malicious stuff.
It's about unknowingly returning values that can break the system.
Maybe it is possible to return specific values that lead to acquire more information/do actions that the eBPF program is not supposed to cause.
I don't have a concrete example, so I will use the word you suggested.
case, as each LSM is carefully reviewed and it won't be accepted if it does not meet the return value conventions.
The biggest problem is when an LSM returns a positive value, instead of a negative value, as it could be converted to a pointer. Since such pointer escapes the IS_ERR() check, its use later in the code can cause unpredictable consequences (e.g. invalid memory access).
Another problem is returning zero when an LSM is supposed to have done some operations. For example, the inode_init_security hook expects that their implementations return zero only if they set the name and value of the new xattr to be added to the new inode. Otherwise, other kernel subsystems might encounter unexpected conditions leading to a crash (e.g. evm_protected_xattr_common() getting NULL as argument).
Finally, there are LSM hooks which are supposed to return just one as positive value, or non-negative values. Also in these cases, although it seems less critical, it is safer to return to callers of the LSM infrastructure more precisely what they expect.
As eBPF allows code outside the kernel to run, it is its responsibility to ensure that only expected values are returned to LSM infrastructure callers.
Create four new BTF ID sets, respectively for hooks that can return positive values, only one as positive value, that cannot return zero, and that cannot return negative values. Create also corresponding functions to check if the hook a security module is attached to belongs to one of the defined sets.
Finally, check in the eBPF verifier the value returned by security modules for each attached LSM hook, and return -EINVAL (the security module cannot run) if the hook implementation does not satisfy the hook return value policy.
Cc: stable@vger.kernel.org Fixes: 9d3fdea789c8 ("bpf: lsm: Provide attachment points for BPF LSM programs") Signed-off-by: Roberto Sassu roberto.sassu@huawei.com
include/linux/bpf_lsm.h | 24 ++++++++++++++++++ kernel/bpf/bpf_lsm.c | 56 +++++++++++++++++++++++++++++++++++++++++ kernel/bpf/verifier.c | 35 +++++++++++++++++++++++--- 3 files changed, 112 insertions(+), 3 deletions(-)
diff --git a/include/linux/bpf_lsm.h b/include/linux/bpf_lsm.h index 4bcf76a9bb06..cd38aca4cfc0 100644 --- a/include/linux/bpf_lsm.h +++ b/include/linux/bpf_lsm.h @@ -28,6 +28,10 @@ int bpf_lsm_verify_prog(struct bpf_verifier_log *vlog, const struct bpf_prog *prog);
bool bpf_lsm_is_sleepable_hook(u32 btf_id); +bool bpf_lsm_can_ret_pos_value(u32 btf_id); +bool bpf_lsm_can_ret_only_one_as_pos_value(u32 btf_id); +bool bpf_lsm_cannot_ret_zero(u32 btf_id); +bool bpf_lsm_cannot_ret_neg_value(u32 btf_id);
This does not need to be exported to the rest of the kernel. Please have this logic in bpf_lsm.c and export a single verify function.
Also, these really don't need to be such scattered logic, Could we somehow encode this into the LSM_HOOK definition?
The problem is that a new LSM_HOOK definition would apply to every LSM hook, while we need the ability to select subsets.
I was thinking, but I didn't check yet, what about using BTF_ID_FLAGS, introducing a flag for each interval (<0, 0, 1, >1) and setting the appropriate flags for each LSM hook?
Before adding infra to all hooks, let's analyze all hooks first. I thought the number of exceptions is very small. 99% of hooks will be fine with IS_ERR. If so, adding an extra flag to every hook will cause too much churn.
On Fri, 2022-11-04 at 17:42 -0700, Alexei Starovoitov wrote:
On Fri, Nov 4, 2022 at 8:29 AM Roberto Sassu roberto.sassu@huaweicloud.com wrote:
On Thu, 2022-11-03 at 16:09 +0100, KP Singh wrote:
On Fri, Oct 28, 2022 at 6:55 PM Roberto Sassu roberto.sassu@huaweicloud.com wrote:
From: Roberto Sassu roberto.sassu@huawei.com
BPF LSM defines a bpf_lsm_*() function for each LSM hook, so that security modules can define their own implementation for the desired hooks.
Unfortunately, BPF LSM does not restrict which values security modules can return (for non-void LSM hooks). Security modules might follow the conventions stated in include/linux/lsm_hooks.h, or put arbitrary values.
This could cause big troubles, as the kernel is not ready to handle possibly malicious return values from LSMs. Until now, it was not the
I am not sure I would call this malicious. This would be incorrect, if someone is writing a BPF LSM program they already have the powers to willingly do a lot of malicious stuff.
It's about unknowingly returning values that can break the system.
Maybe it is possible to return specific values that lead to acquire more information/do actions that the eBPF program is not supposed to cause.
I don't have a concrete example, so I will use the word you suggested.
case, as each LSM is carefully reviewed and it won't be accepted if it does not meet the return value conventions.
The biggest problem is when an LSM returns a positive value, instead of a negative value, as it could be converted to a pointer. Since such pointer escapes the IS_ERR() check, its use later in the code can cause unpredictable consequences (e.g. invalid memory access).
Another problem is returning zero when an LSM is supposed to have done some operations. For example, the inode_init_security hook expects that their implementations return zero only if they set the name and value of the new xattr to be added to the new inode. Otherwise, other kernel subsystems might encounter unexpected conditions leading to a crash (e.g. evm_protected_xattr_common() getting NULL as argument).
Finally, there are LSM hooks which are supposed to return just one as positive value, or non-negative values. Also in these cases, although it seems less critical, it is safer to return to callers of the LSM infrastructure more precisely what they expect.
As eBPF allows code outside the kernel to run, it is its responsibility to ensure that only expected values are returned to LSM infrastructure callers.
Create four new BTF ID sets, respectively for hooks that can return positive values, only one as positive value, that cannot return zero, and that cannot return negative values. Create also corresponding functions to check if the hook a security module is attached to belongs to one of the defined sets.
Finally, check in the eBPF verifier the value returned by security modules for each attached LSM hook, and return -EINVAL (the security module cannot run) if the hook implementation does not satisfy the hook return value policy.
Cc: stable@vger.kernel.org Fixes: 9d3fdea789c8 ("bpf: lsm: Provide attachment points for BPF LSM programs") Signed-off-by: Roberto Sassu roberto.sassu@huawei.com
include/linux/bpf_lsm.h | 24 ++++++++++++++++++ kernel/bpf/bpf_lsm.c | 56 +++++++++++++++++++++++++++++++++++++++++ kernel/bpf/verifier.c | 35 +++++++++++++++++++++++--- 3 files changed, 112 insertions(+), 3 deletions(-)
diff --git a/include/linux/bpf_lsm.h b/include/linux/bpf_lsm.h index 4bcf76a9bb06..cd38aca4cfc0 100644 --- a/include/linux/bpf_lsm.h +++ b/include/linux/bpf_lsm.h @@ -28,6 +28,10 @@ int bpf_lsm_verify_prog(struct bpf_verifier_log *vlog, const struct bpf_prog *prog);
bool bpf_lsm_is_sleepable_hook(u32 btf_id); +bool bpf_lsm_can_ret_pos_value(u32 btf_id); +bool bpf_lsm_can_ret_only_one_as_pos_value(u32 btf_id); +bool bpf_lsm_cannot_ret_zero(u32 btf_id); +bool bpf_lsm_cannot_ret_neg_value(u32 btf_id);
This does not need to be exported to the rest of the kernel. Please have this logic in bpf_lsm.c and export a single verify function.
Also, these really don't need to be such scattered logic, Could we somehow encode this into the LSM_HOOK definition?
The problem is that a new LSM_HOOK definition would apply to every LSM hook, while we need the ability to select subsets.
I was thinking, but I didn't check yet, what about using BTF_ID_FLAGS, introducing a flag for each interval (<0, 0, 1, >1) and setting the appropriate flags for each LSM hook?
Before adding infra to all hooks, let's analyze all hooks first. I thought the number of exceptions is very small. 99% of hooks will be fine with IS_ERR. If so, adding an extra flag to every hook will cause too much churn.
If I counted them correctly, there are 12 hooks which can return a positive value. Among them, 6 can return only 1. 3 should not return a negative value.
A reason for making this change in the LSM infrastructure would be that the return values provided there would be the official reference for anyone dealing with LSM hooks (e.g. redefining the LSM_HOOK macro).
Another reason would be that for new hooks, the developer introducing them would have to provide the information. BPF LSM would use that automatically (otherwise it might get out of sync).
The idea would be to use BTF_ID_FLAGS() with the flags coming from lsm_hook_defs.h, and to check if a flag is set depending on the interval of the return value provided by the eBPF program.
Roberto
On Mon, Nov 7, 2022 at 4:33 AM Roberto Sassu roberto.sassu@huaweicloud.com wrote:
On Fri, 2022-11-04 at 17:42 -0700, Alexei Starovoitov wrote:
On Fri, Nov 4, 2022 at 8:29 AM Roberto Sassu roberto.sassu@huaweicloud.com wrote:
On Thu, 2022-11-03 at 16:09 +0100, KP Singh wrote:
On Fri, Oct 28, 2022 at 6:55 PM Roberto Sassu roberto.sassu@huaweicloud.com wrote:
From: Roberto Sassu roberto.sassu@huawei.com
BPF LSM defines a bpf_lsm_*() function for each LSM hook, so that security modules can define their own implementation for the desired hooks.
Unfortunately, BPF LSM does not restrict which values security modules can return (for non-void LSM hooks). Security modules might follow the conventions stated in include/linux/lsm_hooks.h, or put arbitrary values.
This could cause big troubles, as the kernel is not ready to handle possibly malicious return values from LSMs. Until now, it was not the
I am not sure I would call this malicious. This would be incorrect, if someone is writing a BPF LSM program they already have the powers to willingly do a lot of malicious stuff.
It's about unknowingly returning values that can break the system.
Maybe it is possible to return specific values that lead to acquire more information/do actions that the eBPF program is not supposed to cause.
I don't have a concrete example, so I will use the word you suggested.
case, as each LSM is carefully reviewed and it won't be accepted if it does not meet the return value conventions.
The biggest problem is when an LSM returns a positive value, instead of a negative value, as it could be converted to a pointer. Since such pointer escapes the IS_ERR() check, its use later in the code can cause unpredictable consequences (e.g. invalid memory access).
Another problem is returning zero when an LSM is supposed to have done some operations. For example, the inode_init_security hook expects that their implementations return zero only if they set the name and value of the new xattr to be added to the new inode. Otherwise, other kernel subsystems might encounter unexpected conditions leading to a crash (e.g. evm_protected_xattr_common() getting NULL as argument).
Finally, there are LSM hooks which are supposed to return just one as positive value, or non-negative values. Also in these cases, although it seems less critical, it is safer to return to callers of the LSM infrastructure more precisely what they expect.
As eBPF allows code outside the kernel to run, it is its responsibility to ensure that only expected values are returned to LSM infrastructure callers.
Create four new BTF ID sets, respectively for hooks that can return positive values, only one as positive value, that cannot return zero, and that cannot return negative values. Create also corresponding functions to check if the hook a security module is attached to belongs to one of the defined sets.
Finally, check in the eBPF verifier the value returned by security modules for each attached LSM hook, and return -EINVAL (the security module cannot run) if the hook implementation does not satisfy the hook return value policy.
Cc: stable@vger.kernel.org Fixes: 9d3fdea789c8 ("bpf: lsm: Provide attachment points for BPF LSM programs") Signed-off-by: Roberto Sassu roberto.sassu@huawei.com
include/linux/bpf_lsm.h | 24 ++++++++++++++++++ kernel/bpf/bpf_lsm.c | 56 +++++++++++++++++++++++++++++++++++++++++ kernel/bpf/verifier.c | 35 +++++++++++++++++++++++--- 3 files changed, 112 insertions(+), 3 deletions(-)
diff --git a/include/linux/bpf_lsm.h b/include/linux/bpf_lsm.h index 4bcf76a9bb06..cd38aca4cfc0 100644 --- a/include/linux/bpf_lsm.h +++ b/include/linux/bpf_lsm.h @@ -28,6 +28,10 @@ int bpf_lsm_verify_prog(struct bpf_verifier_log *vlog, const struct bpf_prog *prog);
bool bpf_lsm_is_sleepable_hook(u32 btf_id); +bool bpf_lsm_can_ret_pos_value(u32 btf_id); +bool bpf_lsm_can_ret_only_one_as_pos_value(u32 btf_id); +bool bpf_lsm_cannot_ret_zero(u32 btf_id); +bool bpf_lsm_cannot_ret_neg_value(u32 btf_id);
This does not need to be exported to the rest of the kernel. Please have this logic in bpf_lsm.c and export a single verify function.
Also, these really don't need to be such scattered logic, Could we somehow encode this into the LSM_HOOK definition?
The problem is that a new LSM_HOOK definition would apply to every LSM hook, while we need the ability to select subsets.
I was thinking, but I didn't check yet, what about using BTF_ID_FLAGS, introducing a flag for each interval (<0, 0, 1, >1) and setting the appropriate flags for each LSM hook?
Before adding infra to all hooks, let's analyze all hooks first. I thought the number of exceptions is very small. 99% of hooks will be fine with IS_ERR. If so, adding an extra flag to every hook will cause too much churn.
If I counted them correctly, there are 12 hooks which can return a positive value. Among them, 6 can return only 1. 3 should not return a negative value.
A reason for making this change in the LSM infrastructure would be that the return values provided there would be the official reference for anyone dealing with LSM hooks (e.g. redefining the LSM_HOOK macro).
Another reason would be that for new hooks, the developer introducing them would have to provide the information. BPF LSM would use that automatically (otherwise it might get out of sync).
I'd prefer these 12 hooks to get converted to IS_ERR instead. Especially those that can only return 1... why aren't they void?
The idea would be to use BTF_ID_FLAGS() with the flags coming from lsm_hook_defs.h, and to check if a flag is set depending on the interval of the return value provided by the eBPF program.
BTF_ID_FLAGS is not appropriate for this.
On Mon, 2022-11-07 at 08:00 -0800, Alexei Starovoitov wrote:
On Mon, Nov 7, 2022 at 4:33 AM Roberto Sassu roberto.sassu@huaweicloud.com wrote:
On Fri, 2022-11-04 at 17:42 -0700, Alexei Starovoitov wrote:
On Fri, Nov 4, 2022 at 8:29 AM Roberto Sassu roberto.sassu@huaweicloud.com wrote:
On Thu, 2022-11-03 at 16:09 +0100, KP Singh wrote:
On Fri, Oct 28, 2022 at 6:55 PM Roberto Sassu roberto.sassu@huaweicloud.com wrote:
From: Roberto Sassu roberto.sassu@huawei.com
BPF LSM defines a bpf_lsm_*() function for each LSM hook, so that security modules can define their own implementation for the desired hooks.
Unfortunately, BPF LSM does not restrict which values security modules can return (for non-void LSM hooks). Security modules might follow the conventions stated in include/linux/lsm_hooks.h, or put arbitrary values.
This could cause big troubles, as the kernel is not ready to handle possibly malicious return values from LSMs. Until now, it was not the
I am not sure I would call this malicious. This would be incorrect, if someone is writing a BPF LSM program they already have the powers to willingly do a lot of malicious stuff.
It's about unknowingly returning values that can break the system.
Maybe it is possible to return specific values that lead to acquire more information/do actions that the eBPF program is not supposed to cause.
I don't have a concrete example, so I will use the word you suggested.
case, as each LSM is carefully reviewed and it won't be accepted if it does not meet the return value conventions.
The biggest problem is when an LSM returns a positive value, instead of a negative value, as it could be converted to a pointer. Since such pointer escapes the IS_ERR() check, its use later in the code can cause unpredictable consequences (e.g. invalid memory access).
Another problem is returning zero when an LSM is supposed to have done some operations. For example, the inode_init_security hook expects that their implementations return zero only if they set the name and value of the new xattr to be added to the new inode. Otherwise, other kernel subsystems might encounter unexpected conditions leading to a crash (e.g. evm_protected_xattr_common() getting NULL as argument).
Finally, there are LSM hooks which are supposed to return just one as positive value, or non-negative values. Also in these cases, although it seems less critical, it is safer to return to callers of the LSM infrastructure more precisely what they expect.
As eBPF allows code outside the kernel to run, it is its responsibility to ensure that only expected values are returned to LSM infrastructure callers.
Create four new BTF ID sets, respectively for hooks that can return positive values, only one as positive value, that cannot return zero, and that cannot return negative values. Create also corresponding functions to check if the hook a security module is attached to belongs to one of the defined sets.
Finally, check in the eBPF verifier the value returned by security modules for each attached LSM hook, and return -EINVAL (the security module cannot run) if the hook implementation does not satisfy the hook return value policy.
Cc: stable@vger.kernel.org Fixes: 9d3fdea789c8 ("bpf: lsm: Provide attachment points for BPF LSM programs") Signed-off-by: Roberto Sassu roberto.sassu@huawei.com
include/linux/bpf_lsm.h | 24 ++++++++++++++++++ kernel/bpf/bpf_lsm.c | 56 +++++++++++++++++++++++++++++++++++++++++ kernel/bpf/verifier.c | 35 +++++++++++++++++++++++--- 3 files changed, 112 insertions(+), 3 deletions(-)
diff --git a/include/linux/bpf_lsm.h b/include/linux/bpf_lsm.h index 4bcf76a9bb06..cd38aca4cfc0 100644 --- a/include/linux/bpf_lsm.h +++ b/include/linux/bpf_lsm.h @@ -28,6 +28,10 @@ int bpf_lsm_verify_prog(struct bpf_verifier_log *vlog, const struct bpf_prog *prog);
bool bpf_lsm_is_sleepable_hook(u32 btf_id); +bool bpf_lsm_can_ret_pos_value(u32 btf_id); +bool bpf_lsm_can_ret_only_one_as_pos_value(u32 btf_id); +bool bpf_lsm_cannot_ret_zero(u32 btf_id); +bool bpf_lsm_cannot_ret_neg_value(u32 btf_id);
This does not need to be exported to the rest of the kernel. Please have this logic in bpf_lsm.c and export a single verify function.
Also, these really don't need to be such scattered logic, Could we somehow encode this into the LSM_HOOK definition?
The problem is that a new LSM_HOOK definition would apply to every LSM hook, while we need the ability to select subsets.
I was thinking, but I didn't check yet, what about using BTF_ID_FLAGS, introducing a flag for each interval (<0, 0, 1, >1) and setting the appropriate flags for each LSM hook?
Before adding infra to all hooks, let's analyze all hooks first. I thought the number of exceptions is very small. 99% of hooks will be fine with IS_ERR. If so, adding an extra flag to every hook will cause too much churn.
If I counted them correctly, there are 12 hooks which can return a positive value. Among them, 6 can return only 1. 3 should not return a negative value.
A reason for making this change in the LSM infrastructure would be that the return values provided there would be the official reference for anyone dealing with LSM hooks (e.g. redefining the LSM_HOOK macro).
Another reason would be that for new hooks, the developer introducing them would have to provide the information. BPF LSM would use that automatically (otherwise it might get out of sync).
I'd prefer these 12 hooks to get converted to IS_ERR instead. Especially those that can only return 1... why aren't they void?
Sorry, I meant can only return 1 as positive value (but can return 0 or a negative value).
Not sure it is a good idea to change the conventions.
The idea would be to use BTF_ID_FLAGS() with the flags coming from lsm_hook_defs.h, and to check if a flag is set depending on the interval of the return value provided by the eBPF program.
BTF_ID_FLAGS is not appropriate for this.
Uhm, why not? If you store the flags in the BTF ID set, the implementation would be something like this.
Assuming that a hook definition becomes:
LSM_HOOK(int, 0, LSM_RET_NEG | LSM_RET_ZERO, path_unlink, const struct path *dir, struct dentry *dentry)
In bpf_lsm.c, we would have:
#include <linux/lsm_hook_defs.h> #undef LSM_HOOK
#define LSM_HOOK(RET, DEFAULT, RET_FLAGS, NAME, ...) \ BTF_ID_FLAGS(func, bpf_lsm_##NAME, RET_FLAGS) BTF_SET_START(bpf_lsm_hooks) #include <linux/lsm_hook_defs.h> #undef LSM_HOOK BTF_SET_END(bpf_lsm_hooks)
bool bpf_lsm_ret_value_allowed(u32 btf_id, ...) { u32 *flags = btf_id_set8_contains(&bpf_lsm_hooks, btf_id);
if (lsm_ret < 0 && !(*flags & LSM_RET_NEG)) return false;
...
return true; }
Thanks
Roberto
From: Roberto Sassu roberto.sassu@huawei.com
Ensure that the eBPF verifier allows to load only LSM programs that return an allowed value depending on the LSM hook they attach to.
Signed-off-by: Roberto Sassu roberto.sassu@huawei.com --- .../testing/selftests/bpf/verifier/lsm_ret.c | 148 ++++++++++++++++++ 1 file changed, 148 insertions(+) create mode 100644 tools/testing/selftests/bpf/verifier/lsm_ret.c
diff --git a/tools/testing/selftests/bpf/verifier/lsm_ret.c b/tools/testing/selftests/bpf/verifier/lsm_ret.c new file mode 100644 index 000000000000..1a11f47fb24a --- /dev/null +++ b/tools/testing/selftests/bpf/verifier/lsm_ret.c @@ -0,0 +1,148 @@ +{ + "lsm return value: positive not allowed, return -EPERM", + .insns = { + BPF_MOV64_IMM(BPF_REG_0, -EPERM), + BPF_EXIT_INSN(), + }, + .prog_type = BPF_PROG_TYPE_LSM, + .kfunc = "inode_permission", + .expected_attach_type = BPF_LSM_MAC, + .result = ACCEPT, +}, +{ + "lsm return value: positive not allowed, return zero", + .insns = { + BPF_MOV64_IMM(BPF_REG_0, 0), + BPF_EXIT_INSN(), + }, + .prog_type = BPF_PROG_TYPE_LSM, + .kfunc = "inode_permission", + .expected_attach_type = BPF_LSM_MAC, + .result = ACCEPT, +}, +{ + "lsm return value: positive not allowed, return one", + .insns = { + BPF_MOV64_IMM(BPF_REG_0, 1), + BPF_EXIT_INSN(), + }, + .prog_type = BPF_PROG_TYPE_LSM, + .kfunc = "inode_permission", + .expected_attach_type = BPF_LSM_MAC, + .errstr = "Invalid R0, cannot return positive value", + .result = REJECT, +}, +{ + "lsm return value: zero/positive not allowed, return -EPERM", + .insns = { + BPF_MOV64_IMM(BPF_REG_0, -EPERM), + BPF_EXIT_INSN(), + }, + .prog_type = BPF_PROG_TYPE_LSM, + .kfunc = "inode_init_security", + .expected_attach_type = BPF_LSM_MAC, + .result = ACCEPT, +}, +{ + "lsm return value: zero/positive not allowed, return zero", + .insns = { + BPF_MOV64_IMM(BPF_REG_0, 0), + BPF_EXIT_INSN(), + }, + .prog_type = BPF_PROG_TYPE_LSM, + .kfunc = "inode_init_security", + .expected_attach_type = BPF_LSM_MAC, + .errstr = "Invalid R0, cannot return zero value", + .result = REJECT, +}, +{ + "lsm return value: zero/positive not allowed, return one", + .insns = { + BPF_MOV64_IMM(BPF_REG_0, 1), + BPF_EXIT_INSN(), + }, + .prog_type = BPF_PROG_TYPE_LSM, + .kfunc = "inode_init_security", + .expected_attach_type = BPF_LSM_MAC, + .errstr = "Invalid R0, cannot return positive value", + .result = REJECT, +}, +{ + "lsm return value: positive allowed, return one", + .insns = { + BPF_MOV64_IMM(BPF_REG_0, 1), + BPF_EXIT_INSN(), + }, + .prog_type = BPF_PROG_TYPE_LSM, + .kfunc = "getprocattr", + .expected_attach_type = BPF_LSM_MAC, + .result = ACCEPT, +}, +{ + "lsm return value: positive allowed, return two", + .insns = { + BPF_MOV64_IMM(BPF_REG_0, 2), + BPF_EXIT_INSN(), + }, + .prog_type = BPF_PROG_TYPE_LSM, + .kfunc = "getprocattr", + .expected_attach_type = BPF_LSM_MAC, + .result = ACCEPT, +}, +{ + "lsm return value: only one allowed, return one", + .insns = { + BPF_MOV64_IMM(BPF_REG_0, 1), + BPF_EXIT_INSN(), + }, + .prog_type = BPF_PROG_TYPE_LSM, + .kfunc = "audit_rule_match", + .expected_attach_type = BPF_LSM_MAC, + .result = ACCEPT, +}, +{ + "lsm return value: only one allowed, return two", + .insns = { + BPF_MOV64_IMM(BPF_REG_0, 2), + BPF_EXIT_INSN(), + }, + .prog_type = BPF_PROG_TYPE_LSM, + .kfunc = "audit_rule_match", + .expected_attach_type = BPF_LSM_MAC, + .errstr = "Invalid R0, can return only one as positive value", + .result = REJECT, +}, +{ + "lsm return value: negative not allowed, return -EPERM", + .insns = { + BPF_MOV64_IMM(BPF_REG_0, -EPERM), + BPF_EXIT_INSN(), + }, + .prog_type = BPF_PROG_TYPE_LSM, + .kfunc = "vm_enough_memory", + .expected_attach_type = BPF_LSM_MAC, + .errstr = "Invalid R0, cannot return negative value", + .result = REJECT, +}, +{ + "lsm return value: negative not allowed, return zero", + .insns = { + BPF_MOV64_IMM(BPF_REG_0, 0), + BPF_EXIT_INSN(), + }, + .prog_type = BPF_PROG_TYPE_LSM, + .kfunc = "vm_enough_memory", + .expected_attach_type = BPF_LSM_MAC, + .result = ACCEPT, +}, +{ + "lsm return value: negative not allowed, return one", + .insns = { + BPF_MOV64_IMM(BPF_REG_0, 1), + BPF_EXIT_INSN(), + }, + .prog_type = BPF_PROG_TYPE_LSM, + .kfunc = "vm_enough_memory", + .expected_attach_type = BPF_LSM_MAC, + .result = ACCEPT, +},
On Fri, Oct 28, 2022 at 6:55 PM Roberto Sassu roberto.sassu@huaweicloud.com wrote:
From: Roberto Sassu roberto.sassu@huawei.com
include/linux/lsm_hooks.h reports the result of the LSM infrastructure to the callers, not what LSMs should return to the LSM infrastructure.
Clarify that and add that returning 1 from the LSMs means calling __vm_enough_memory() with cap_sys_admin set, 0 without.
Signed-off-by: Roberto Sassu roberto.sassu@huawei.com
Reviewed-by: KP Singh kpsingh@kernel.org
include/linux/lsm_hooks.h | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h index 4ec80b96c22e..f40b82ca91e7 100644 --- a/include/linux/lsm_hooks.h +++ b/include/linux/lsm_hooks.h @@ -1411,7 +1411,9 @@
Check permissions for allocating a new virtual mapping.@mm contains the mm struct it is being added to.@pages contains the number of pages.
Return 0 if permission is granted.
Return 0 if permission is granted by LSMs to the caller. LSMs should
return 1 if __vm_enough_memory() should be called with
cap_sys_admin set, 0 if not.- @ismaclabel:
Check if the extended attribute specified by @name-- 2.25.1
linux-kselftest-mirror@lists.linaro.org
-
Alexei Starovoitov -
KP Singh -
Roberto Sassu