commit 29bc22ac5e5bc63275e850f0c8fc549e3d0e306b upstream.
Save the 'struct cred' associated with a binder process at initial open to avoid potential race conditions when converting to an euid.
Set a transaction's sender_euid from the 'struct cred' saved at binder_open() instead of looking up the euid from the binder proc's 'struct task'. This ensures the euid is associated with the security context that of the task that opened binder.
Cc: stable@vger.kernel.org # 4.4+ Fixes: 457b9a6f09f0 ("Staging: android: add binder driver") Signed-off-by: Todd Kjos tkjos@google.com Suggested-by: Stephen Smalley stephen.smalley.work@gmail.com Suggested-by: Jann Horn jannh@google.com Acked-by: Casey Schaufler casey@schaufler-ca.com Signed-off-by: Paul Moore paul@paul-moore.com Change-Id: I91922e7f359df5901749f1b09094c3c68d45aed4 --- drivers/android/binder.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-)
diff --git a/drivers/android/binder.c b/drivers/android/binder.c index 65b22b5af51a..4e33f6e42ac4 100644 --- a/drivers/android/binder.c +++ b/drivers/android/binder.c @@ -420,6 +420,9 @@ enum binder_deferred_state { * (invariant after initialized) * @tsk task_struct for group_leader of process * (invariant after initialized) + * @cred struct cred associated with the `struct file` + * in binder_open() + * (invariant after initialized) * @deferred_work_node: element for binder_deferred_list * (protected by binder_deferred_lock) * @deferred_work: bitmap of deferred work to perform @@ -465,6 +468,7 @@ struct binder_proc { struct list_head waiting_threads; int pid; struct task_struct *tsk; + const struct cred *cred; struct hlist_node deferred_work_node; int deferred_work; bool is_dead; @@ -3088,7 +3092,7 @@ static void binder_transaction(struct binder_proc *proc, t->from = thread; else t->from = NULL; - t->sender_euid = task_euid(proc->tsk); + t->sender_euid = proc->cred->euid; t->to_proc = target_proc; t->to_thread = target_thread; t->code = tr->code; @@ -4703,6 +4707,7 @@ static void binder_free_proc(struct binder_proc *proc) } binder_alloc_deferred_release(&proc->alloc); put_task_struct(proc->tsk); + put_cred(proc->cred); binder_stats_deleted(BINDER_STAT_PROC); kfree(proc); } @@ -5220,6 +5225,7 @@ static int binder_open(struct inode *nodp, struct file *filp) spin_lock_init(&proc->outer_lock); get_task_struct(current->group_leader); proc->tsk = current->group_leader; + proc->cred = get_cred(filp->f_cred); INIT_LIST_HEAD(&proc->todo); proc->default_priority = task_nice(current); /* binderfs stashes devices in i_private */
commit 52f88693378a58094c538662ba652aff0253c4fe upstream.
Since binder was integrated with selinux, it has passed 'struct task_struct' associated with the binder_proc to represent the source and target of transactions. The conversion of task to SID was then done in the hook implementations. It turns out that there are race conditions which can result in an incorrect security context being used.
Fix by using the 'struct cred' saved during binder_open and pass it to the selinux subsystem.
Cc: stable@vger.kernel.org # 5.14 (need backport for earlier stables) Fixes: 79af73079d75 ("Add security hooks to binder and implement the hooks for SELinux.") Suggested-by: Jann Horn jannh@google.com Signed-off-by: Todd Kjos tkjos@google.com Acked-by: Casey Schaufler casey@schaufler-ca.com Signed-off-by: Paul Moore paul@paul-moore.com Change-Id: Id7157515d2b08f11683aeb8ad9b8f1da075d34e7 --- drivers/android/binder.c | 12 ++++++------ include/linux/lsm_hook_defs.h | 14 +++++++------- include/linux/lsm_hooks.h | 14 +++++++------- include/linux/security.h | 28 +++++++++++++-------------- security/security.c | 14 +++++++------- security/selinux/hooks.c | 36 +++++++++++++++-------------------- 6 files changed, 56 insertions(+), 62 deletions(-)
diff --git a/drivers/android/binder.c b/drivers/android/binder.c index 4e33f6e42ac4..50fff726dc70 100644 --- a/drivers/android/binder.c +++ b/drivers/android/binder.c @@ -2444,7 +2444,7 @@ static int binder_translate_binder(struct flat_binder_object *fp, ret = -EINVAL; goto done; } - if (security_binder_transfer_binder(proc->tsk, target_proc->tsk)) { + if (security_binder_transfer_binder(proc->cred, target_proc->cred)) { ret = -EPERM; goto done; } @@ -2490,7 +2490,7 @@ static int binder_translate_handle(struct flat_binder_object *fp, proc->pid, thread->pid, fp->handle); return -EINVAL; } - if (security_binder_transfer_binder(proc->tsk, target_proc->tsk)) { + if (security_binder_transfer_binder(proc->cred, target_proc->cred)) { ret = -EPERM; goto done; } @@ -2578,7 +2578,7 @@ static int binder_translate_fd(u32 fd, binder_size_t fd_offset, ret = -EBADF; goto err_fget; } - ret = security_binder_transfer_file(proc->tsk, target_proc->tsk, file); + ret = security_binder_transfer_file(proc->cred, target_proc->cred, file); if (ret < 0) { ret = -EPERM; goto err_security; @@ -2976,8 +2976,8 @@ static void binder_transaction(struct binder_proc *proc, return_error_line = __LINE__; goto err_invalid_target_handle; } - if (security_binder_transaction(proc->tsk, - target_proc->tsk) < 0) { + if (security_binder_transaction(proc->cred, + target_proc->cred) < 0) { return_error = BR_FAILED_REPLY; return_error_param = -EPERM; return_error_line = __LINE__; @@ -4918,7 +4918,7 @@ static int binder_ioctl_set_ctx_mgr(struct file *filp, ret = -EBUSY; goto out; } - ret = security_binder_set_context_mgr(proc->tsk); + ret = security_binder_set_context_mgr(proc->cred); if (ret < 0) goto out; if (uid_valid(context->binder_context_mgr_uid)) { diff --git a/include/linux/lsm_hook_defs.h b/include/linux/lsm_hook_defs.h index 32a940117e7a..a6a3d4ddfc2d 100644 --- a/include/linux/lsm_hook_defs.h +++ b/include/linux/lsm_hook_defs.h @@ -26,13 +26,13 @@ * #undef LSM_HOOK * }; */ -LSM_HOOK(int, 0, binder_set_context_mgr, struct task_struct *mgr) -LSM_HOOK(int, 0, binder_transaction, struct task_struct *from, - struct task_struct *to) -LSM_HOOK(int, 0, binder_transfer_binder, struct task_struct *from, - struct task_struct *to) -LSM_HOOK(int, 0, binder_transfer_file, struct task_struct *from, - struct task_struct *to, struct file *file) +LSM_HOOK(int, 0, binder_set_context_mgr, const struct cred *mgr) +LSM_HOOK(int, 0, binder_transaction, const struct cred *from, + const struct cred *to) +LSM_HOOK(int, 0, binder_transfer_binder, const struct cred *from, + const struct cred *to) +LSM_HOOK(int, 0, binder_transfer_file, const struct cred *from, + const struct cred *to, struct file *file) LSM_HOOK(int, 0, ptrace_access_check, struct task_struct *child, unsigned int mode) LSM_HOOK(int, 0, ptrace_traceme, struct task_struct *parent) diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h index c503f7ab8afb..a8531b37e6f5 100644 --- a/include/linux/lsm_hooks.h +++ b/include/linux/lsm_hooks.h @@ -1288,22 +1288,22 @@ * * @binder_set_context_mgr: * Check whether @mgr is allowed to be the binder context manager. - * @mgr contains the task_struct for the task being registered. + * @mgr contains the struct cred for the current binder process. * Return 0 if permission is granted. * @binder_transaction: * Check whether @from is allowed to invoke a binder transaction call * to @to. - * @from contains the task_struct for the sending task. - * @to contains the task_struct for the receiving task. + * @from contains the struct cred for the sending process. + * @to contains the struct cred for the receiving process. * @binder_transfer_binder: * Check whether @from is allowed to transfer a binder reference to @to. - * @from contains the task_struct for the sending task. - * @to contains the task_struct for the receiving task. + * @from contains the struct cred for the sending process. + * @to contains the struct cred for the receiving process. * @binder_transfer_file: * Check whether @from is allowed to transfer @file to @to. - * @from contains the task_struct for the sending task. + * @from contains the struct cred for the sending process. * @file contains the struct file being transferred. - * @to contains the task_struct for the receiving task. + * @to contains the struct cred for the receiving process. * * @ptrace_access_check: * Check permission before allowing the current process to trace the diff --git a/include/linux/security.h b/include/linux/security.h index 7ef74d01b8e7..e67cc8c40865 100644 --- a/include/linux/security.h +++ b/include/linux/security.h @@ -254,13 +254,13 @@ extern int security_init(void); extern int early_security_init(void);
/* Security operations */ -int security_binder_set_context_mgr(struct task_struct *mgr); -int security_binder_transaction(struct task_struct *from, - struct task_struct *to); -int security_binder_transfer_binder(struct task_struct *from, - struct task_struct *to); -int security_binder_transfer_file(struct task_struct *from, - struct task_struct *to, struct file *file); +int security_binder_set_context_mgr(const struct cred *mgr); +int security_binder_transaction(const struct cred *from, + const struct cred *to); +int security_binder_transfer_binder(const struct cred *from, + const struct cred *to); +int security_binder_transfer_file(const struct cred *from, + const struct cred *to, struct file *file); int security_ptrace_access_check(struct task_struct *child, unsigned int mode); int security_ptrace_traceme(struct task_struct *parent); int security_capget(struct task_struct *target, @@ -493,25 +493,25 @@ static inline int early_security_init(void) return 0; }
-static inline int security_binder_set_context_mgr(struct task_struct *mgr) +static inline int security_binder_set_context_mgr(const struct cred *mgr) { return 0; }
-static inline int security_binder_transaction(struct task_struct *from, - struct task_struct *to) +static inline int security_binder_transaction(const struct cred *from, + const struct cred *to) { return 0; }
-static inline int security_binder_transfer_binder(struct task_struct *from, - struct task_struct *to) +static inline int security_binder_transfer_binder(const struct cred *from, + const struct cred *to) { return 0; }
-static inline int security_binder_transfer_file(struct task_struct *from, - struct task_struct *to, +static inline int security_binder_transfer_file(const struct cred *from, + const struct cred *to, struct file *file) { return 0; diff --git a/security/security.c b/security/security.c index 1c696bce8e1c..a864ff824dd3 100644 --- a/security/security.c +++ b/security/security.c @@ -723,25 +723,25 @@ static void __init lsm_early_task(struct task_struct *task)
/* Security operations */
-int security_binder_set_context_mgr(struct task_struct *mgr) +int security_binder_set_context_mgr(const struct cred *mgr) { return call_int_hook(binder_set_context_mgr, 0, mgr); }
-int security_binder_transaction(struct task_struct *from, - struct task_struct *to) +int security_binder_transaction(const struct cred *from, + const struct cred *to) { return call_int_hook(binder_transaction, 0, from, to); }
-int security_binder_transfer_binder(struct task_struct *from, - struct task_struct *to) +int security_binder_transfer_binder(const struct cred *from, + const struct cred *to) { return call_int_hook(binder_transfer_binder, 0, from, to); }
-int security_binder_transfer_file(struct task_struct *from, - struct task_struct *to, struct file *file) +int security_binder_transfer_file(const struct cred *from, + const struct cred *to, struct file *file) { return call_int_hook(binder_transfer_file, 0, from, to, file); } diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c index 227eb8967963..f32026bc96b4 100644 --- a/security/selinux/hooks.c +++ b/security/selinux/hooks.c @@ -2004,22 +2004,19 @@ static inline u32 open_file_to_av(struct file *file)
/* Hook functions begin here. */
-static int selinux_binder_set_context_mgr(struct task_struct *mgr) +static int selinux_binder_set_context_mgr(const struct cred *mgr) { - u32 mysid = current_sid(); - u32 mgrsid = task_sid(mgr); - return avc_has_perm(&selinux_state, - mysid, mgrsid, SECCLASS_BINDER, + current_sid(), cred_sid(mgr), SECCLASS_BINDER, BINDER__SET_CONTEXT_MGR, NULL); }
-static int selinux_binder_transaction(struct task_struct *from, - struct task_struct *to) +static int selinux_binder_transaction(const struct cred *from, + const struct cred *to) { u32 mysid = current_sid(); - u32 fromsid = task_sid(from); - u32 tosid = task_sid(to); + u32 fromsid = cred_sid(from); + u32 tosid = cred_sid(to); int rc;
if (mysid != fromsid) { @@ -2030,27 +2027,24 @@ static int selinux_binder_transaction(struct task_struct *from, return rc; }
- return avc_has_perm(&selinux_state, - fromsid, tosid, SECCLASS_BINDER, BINDER__CALL, - NULL); + return avc_has_perm(&selinux_state, fromsid, tosid, + SECCLASS_BINDER, BINDER__CALL, NULL); }
-static int selinux_binder_transfer_binder(struct task_struct *from, - struct task_struct *to) +static int selinux_binder_transfer_binder(const struct cred *from, + const struct cred *to) { - u32 fromsid = task_sid(from); - u32 tosid = task_sid(to); - return avc_has_perm(&selinux_state, - fromsid, tosid, SECCLASS_BINDER, BINDER__TRANSFER, + cred_sid(from), cred_sid(to), + SECCLASS_BINDER, BINDER__TRANSFER, NULL); }
-static int selinux_binder_transfer_file(struct task_struct *from, - struct task_struct *to, +static int selinux_binder_transfer_file(const struct cred *from, + const struct cred *to, struct file *file) { - u32 sid = task_sid(to); + u32 sid = cred_sid(to); struct file_security_struct *fsec = selinux_file(file); struct dentry *dentry = file->f_path.dentry; struct inode_security_struct *isec;
commit 4d5b5539742d2554591751b4248b0204d20dcc9d upstream.
Use the 'struct cred' saved at binder_open() to lookup the security ID via security_cred_getsecid(). This ensures that the security context that opened binder is the one used to generate the secctx.
Cc: stable@vger.kernel.org # 5.4+ Fixes: ec74136ded79 ("binder: create node flag to request sender's security context") Signed-off-by: Todd Kjos tkjos@google.com Suggested-by: Stephen Smalley stephen.smalley.work@gmail.com Reported-by: kernel test robot lkp@intel.com Acked-by: Casey Schaufler casey@schaufler-ca.com Signed-off-by: Paul Moore paul@paul-moore.com Change-Id: Ia7b59804a0bdbd51191bbcca556414840307c623 --- drivers/android/binder.c | 2 +- include/linux/security.h | 5 +++++ 2 files changed, 6 insertions(+), 1 deletion(-)
diff --git a/drivers/android/binder.c b/drivers/android/binder.c index 50fff726dc70..3ba3944a9e1f 100644 --- a/drivers/android/binder.c +++ b/drivers/android/binder.c @@ -3103,7 +3103,7 @@ static void binder_transaction(struct binder_proc *proc, u32 secid; size_t added_size;
- security_task_getsecid(proc->tsk, &secid); + security_cred_getsecid(proc->cred, &secid); ret = security_secid_to_secctx(secid, &secctx, &secctx_sz); if (ret) { return_error = BR_FAILED_REPLY; diff --git a/include/linux/security.h b/include/linux/security.h index e67cc8c40865..35355429648e 100644 --- a/include/linux/security.h +++ b/include/linux/security.h @@ -1003,6 +1003,11 @@ static inline void security_transfer_creds(struct cred *new, { }
+static inline void security_cred_getsecid(const struct cred *c, u32 *secid) +{ + *secid = 0; +} + static inline int security_kernel_act_as(struct cred *cred, u32 secid) { return 0;
linux-stable-mirror@lists.linaro.org
-
Todd Kjos