[PATCH 5.17 0512/1126] bpf: Fix a btf decl_tag bug when tagging a function

Greg Kroah-Hartman
2022-04-05T11:21:15Z

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 a3b5a6bf99e7..ac89e65d1692 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -403,6 +403,9 @@ 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
@@ -579,6 +582,7 @@ 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);
}
@@ -3533,9 +3537,24 @@ 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,
@@ -4156,7 +4175,7 @@ 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);

@@ -4246,12 +4265,6 @@ 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;
--
2.34.1