The helper function returns a pointer that in the failure case encodes
an error in the struct btf pointer. The current code lead to Coverity
warning about the use of the invalid pointer:
*** CID 1507963: Memory - illegal accesses (USE_AFTER_FREE)
/kernel/bpf/verifier.c: 1788 in find_kfunc_desc_btf()
1782 return ERR_PTR(-EINVAL);
1783 }
1784
1785 kfunc_btf = __find_kfunc_desc_btf(env, offset, btf_modp);
1786 if (IS_ERR_OR_NULL(kfunc_btf)) {
1787 verbose(env, "cannot find module BTF for func_id %u\n", func_id);
>>> CID 1507963: Memory - illegal accesses (USE_AFTER_FREE)
>>> Using freed pointer "kfunc_btf".
1788 return kfunc_btf ?: ERR_PTR(-ENOENT);
1789 }
1790 return kfunc_btf;
1791 }
1792 return btf_vmlinux ?: ERR_PTR(-ENOENT);
1793 }
Daniel suggested the use of ERR_CAST so that the intended use is clear
to Coverity, but on closer look it seems that we never return NULL from
the helper. Andrii noted that since __find_kfunc_desc_btf already logs
errors for all cases except btf_get_by_fd, it is much easier to add
logging for that and remove the IS_ERR check altogether, returning
directly from it.
Suggested-by: Andrii Nakryiko <andrii@xxxxxxxxxx>
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@xxxxxxxxx>
---
v2->v3
* Remove unused variable (Kernel Test Robot)
v1->v2
* Remove error check, log btf_get_by_fd failure (Andrii)
---
kernel/bpf/verifier.c | 13 ++++---------
1 file changed, 4 insertions(+), 9 deletions(-)
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 20900a1bac12..21cdff35a2f9 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -1727,8 +1727,10 @@ static struct btf *__find_kfunc_desc_btf(struct bpf_verifier_env *env,
return ERR_PTR(-EFAULT);
btf = btf_get_by_fd(btf_fd);
- if (IS_ERR(btf))
+ if (IS_ERR(btf)) {
+ verbose(env, "invalid module BTF fd specified\n");
return btf;
+ }
if (!btf_is_module(btf)) {
verbose(env, "BTF fd for kfunc is not a module BTF\n");
@@ -1771,8 +1773,6 @@ static struct btf *find_kfunc_desc_btf(struct bpf_verifier_env *env,
u32 func_id, s16 offset,
struct module **btf_modp)
{
- struct btf *kfunc_btf;
-
if (offset) {
if (offset < 0) {
/* In the future, this can be allowed to increase limit
@@ -1782,12 +1782,7 @@ static struct btf *find_kfunc_desc_btf(struct bpf_verifier_env *env,
return ERR_PTR(-EINVAL);
}
- kfunc_btf = __find_kfunc_desc_btf(env, offset, btf_modp);
- if (IS_ERR_OR_NULL(kfunc_btf)) {
- verbose(env, "cannot find module BTF for func_id %u\n", func_id);
- return kfunc_btf ?: ERR_PTR(-ENOENT);
- }
- return kfunc_btf;
+ return __find_kfunc_desc_btf(env, offset, btf_modp);
}
return btf_vmlinux ?: ERR_PTR(-ENOENT);
}
--
2.33.0
