[PATCH bpf-next v1 2/2] bpf: Zero kfunc arg meta before error paths can read it

[Amery Hung <ameryhung@gmail.com>]

check_kfunc_call() reads meta.func_name when bpf_fetch_kfunc_arg_meta()
returns -EACCES, but that error can come from fetch_kfunc_meta() (e.g.
fd_array_get_btf() rejecting BTF binding for a signed program) before
meta is memset(), leaving it uninitialized and risking a garbage deref
in verbose().

Move the memset() to the start of bpf_fetch_kfunc_arg_meta() so meta is
zeroed on every error return. The intended "not allowed" -EACCES path
still sets func_name first, so its message is unchanged.

Signed-off-by: Amery Hung <ameryhung@gmail.com>
---
 kernel/bpf/verifier.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index c87e5fec5a85..ddfa4f57016b 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -12571,11 +12571,12 @@ int bpf_fetch_kfunc_arg_meta(struct bpf_verifier_env *env,
 	struct bpf_kfunc_meta kfunc;
 	int err;
 
+	memset(meta, 0, sizeof(*meta));
+
 	err = fetch_kfunc_meta(env, func_id, offset, &kfunc);
 	if (err)
 		return err;
 
-	memset(meta, 0, sizeof(*meta));
 	meta->btf = kfunc.btf;
 	meta->func_id = kfunc.id;
 	meta->func_proto = kfunc.proto;
-- 
2.52.0