From: Yonghong Song yhs@fb.com
[ Upstream commit d7e7b42f4f956f2c68ad8cda87d750093dbba737 ]
syzbot reported a btf decl_tag bug with stack trace below:
general protection fault, probably for non-canonical address 0xdffffc0000000000: 0000 [#1] PREEMPT SMP KASAN KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007] CPU: 0 PID: 3592 Comm: syz-executor914 Not tainted 5.16.0-syzkaller-11424-gb7892f7d5cb2 #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 RIP: 0010:btf_type_vlen include/linux/btf.h:231 [inline] RIP: 0010:btf_decl_tag_resolve+0x83e/0xaa0 kernel/bpf/btf.c:3910 ... Call Trace: <TASK> btf_resolve+0x251/0x1020 kernel/bpf/btf.c:4198 btf_check_all_types kernel/bpf/btf.c:4239 [inline] btf_parse_type_sec kernel/bpf/btf.c:4280 [inline] btf_parse kernel/bpf/btf.c:4513 [inline] btf_new_fd+0x19fe/0x2370 kernel/bpf/btf.c:6047 bpf_btf_load kernel/bpf/syscall.c:4039 [inline] __sys_bpf+0x1cbb/0x5970 kernel/bpf/syscall.c:4679 __do_sys_bpf kernel/bpf/syscall.c:4738 [inline] __se_sys_bpf kernel/bpf/syscall.c:4736 [inline] __x64_sys_bpf+0x75/0xb0 kernel/bpf/syscall.c:4736 do_syscall_x64 arch/x86/entry/common.c:50 [inline] do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80 entry_SYSCALL_64_after_hwframe+0x44/0xae
The kasan error is triggered with an illegal BTF like below: type 0: void type 1: int type 2: decl_tag to func type 3 type 3: func to func_proto type 8 The total number of types is 4 and the type 3 is illegal since its func_proto type is out of range.
Currently, the target type of decl_tag can be struct/union, var or func. Both struct/union and var implemented their own 'resolve' callback functions and hence handled properly in kernel. But func type doesn't have 'resolve' callback function. When btf_decl_tag_resolve() tries to check func type, it tries to get vlen of its func_proto type, which triggered the above kasan error.
To fix the issue, btf_decl_tag_resolve() needs to do btf_func_check() before trying to accessing func_proto type. In the current implementation, func type is checked with btf_func_check() in the main checking function btf_check_all_types(). To fix the above kasan issue, let us implement 'resolve' callback func type properly. The 'resolve' callback will be also called in btf_check_all_types() for func types.
Fixes: b5ea834dde6b ("bpf: Support for new btf kind BTF_KIND_TAG") Reported-by: syzbot+53619be9444215e785ed@syzkaller.appspotmail.com Signed-off-by: Yonghong Song yhs@fb.com Signed-off-by: Alexei Starovoitov ast@kernel.org Acked-by: Martin KaFai Lau kafai@fb.com Link: https://lore.kernel.org/bpf/20220203191727.741862-1-yhs@fb.com Signed-off-by: Sasha Levin sashal@kernel.org --- kernel/bpf/btf.c | 29 +++++++++++++++++++++-------- 1 file changed, 21 insertions(+), 8 deletions(-)
diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c index 1f7967ab9e46..ebbb2f4d3b9c 100644 --- a/kernel/bpf/btf.c +++ b/kernel/bpf/btf.c @@ -401,6 +401,9 @@ static struct btf_type btf_void; static int btf_resolve(struct btf_verifier_env *env, const struct btf_type *t, u32 type_id);
+static int btf_func_check(struct btf_verifier_env *env, + const struct btf_type *t); + static bool btf_type_is_modifier(const struct btf_type *t) { /* Some of them is not strictly a C modifier @@ -576,6 +579,7 @@ static bool btf_type_needs_resolve(const struct btf_type *t) btf_type_is_struct(t) || btf_type_is_array(t) || btf_type_is_var(t) || + btf_type_is_func(t) || btf_type_is_decl_tag(t) || btf_type_is_datasec(t); } @@ -3521,9 +3525,24 @@ static s32 btf_func_check_meta(struct btf_verifier_env *env, return 0; }
+static int btf_func_resolve(struct btf_verifier_env *env, + const struct resolve_vertex *v) +{ + const struct btf_type *t = v->t; + u32 next_type_id = t->type; + int err; + + err = btf_func_check(env, t); + if (err) + return err; + + env_stack_pop_resolved(env, next_type_id, 0); + return 0; +} + static struct btf_kind_operations func_ops = { .check_meta = btf_func_check_meta, - .resolve = btf_df_resolve, + .resolve = btf_func_resolve, .check_member = btf_df_check_member, .check_kflag_member = btf_df_check_kflag_member, .log_details = btf_ref_type_log, @@ -4143,7 +4162,7 @@ static bool btf_resolve_valid(struct btf_verifier_env *env, return !btf_resolved_type_id(btf, type_id) && !btf_resolved_type_size(btf, type_id);
- if (btf_type_is_decl_tag(t)) + if (btf_type_is_decl_tag(t) || btf_type_is_func(t)) return btf_resolved_type_id(btf, type_id) && !btf_resolved_type_size(btf, type_id);
@@ -4233,12 +4252,6 @@ static int btf_check_all_types(struct btf_verifier_env *env) if (err) return err; } - - if (btf_type_is_func(t)) { - err = btf_func_check(env, t); - if (err) - return err; - } }
return 0;