[PATCH 6.18.y] tracing/probes: Fix anon_stack check for unnamed bitfields in btf_find_struct_member

[Sasha Levin <sashal@kernel.org>]

From: "Masami Hiramatsu (Google)" <mhiramat@kernel.org>

[ Upstream commit f36d94a20ca185bcadef3a10b980cd2cfd72d53a ]

btf_find_struct_member() traverses into nested anonymous structures
and unions by pushing members with !member->name_off onto anon_stack.
However, it does not consider the unnamed bitfields (e.g. `int : 5`
or `unsigned int : 0`) which also have member->name_off == 0.

If such an unnamed bitfield is pushed to anon_stack, the
btf_find_struct_member() return an error even if there are other
valid entries in anon_stack.

To fix this, only push unnamed struct/union members to anon_stack.
Also move the btf_type_is_struct() check to the entry of this function
because now it is sure only struct/union are pushed to anon_stack.

Link: https://lore.kernel.org/all/178827249775.123716.7813217688423513612.stgit@devnote2/

Fixes: 302db0f5b3d8 ("tracing/probes: Add a function to search a member of a struct/union")
Cc: stable@vger.kernel.org
Reported-by: Sashiko <sashiko-bot@kernel.org>
Closes: https://lore.kernel.org/all/20260830143859.D56991F00A3D@smtp.kernel.org/
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Reviewed-by: Steven Rostedt <rostedt@goodmis.org>
[ retained the existing kcalloc() allocation instead of upstream’s kzalloc_objs() call. ]
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 kernel/trace/trace_btf.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/kernel/trace/trace_btf.c b/kernel/trace/trace_btf.c
index 5bbdbcbbde3cd..40e66eb59abbc 100644
--- a/kernel/trace/trace_btf.c
+++ b/kernel/trace/trace_btf.c
@@ -74,24 +74,24 @@ const struct btf_member *btf_find_struct_member(struct btf *btf,
 {
 	struct btf_anon_stack *anon_stack;
 	const struct btf_member *member;
+	const struct btf_type *mtype;
 	u32 tid, cur_offset = 0;
 	const char *name;
 	int i, top = 0;
 
+	if (!btf_type_is_struct(type))
+		return ERR_PTR(-EINVAL);
+
 	anon_stack = kcalloc(BTF_ANON_STACK_MAX, sizeof(*anon_stack), GFP_KERNEL);
 	if (!anon_stack)
 		return ERR_PTR(-ENOMEM);
 
 retry:
-	if (!btf_type_is_struct(type)) {
-		member = ERR_PTR(-EINVAL);
-		goto out;
-	}
-
 	for_each_member(i, type, member) {
 		if (!member->name_off) {
 			/* Anonymous union/struct: push it for later use */
-			if (btf_type_skip_modifiers(btf, member->type, &tid) &&
+			mtype = btf_type_skip_modifiers(btf, member->type, &tid);
+			if (mtype && btf_type_is_struct(mtype) &&
 			    top < BTF_ANON_STACK_MAX) {
 				anon_stack[top].tid = tid;
 				anon_stack[top++].offset =
-- 
2.53.0