Re: [PATCH v14 02/14] tracing/probes: Fix BTF kflag check for anonymous struct member access

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:

Pre-existing issues:
- [High] Unnamed bitfields break nested anonymous struct resolution in btf_find_struct_member().
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commit 20a606aa6d4e155be5a531c5d52d78c34205c0b4
Author: Masami Hiramatsu (Google) <mhiramat@kernel.org>

tracing/probes: Fix BTF kflag check for anonymous struct member access

This commit fixes how BTF kflags are checked when traversing nested
anonymous structures and unions in btf_find_struct_member() by using
the actual containing type.

> diff --git a/kernel/trace/trace_btf.c b/kernel/trace/trace_btf.c
> --- a/kernel/trace/trace_btf.c
> +++ b/kernel/trace/trace_btf.c

[ ... ]

> @@ -91,17 +92,23 @@ const struct btf_member *btf_find_struct_member(struct btf *btf,
>  	for_each_member(i, type, member) {
>  		if (!member->name_off) {
>  			/* Anonymous union/struct: push it for later use */
> +			u32 m_off = btf_type_kflag(type) ?
> +				BTF_MEMBER_BIT_OFFSET(member->offset) :
> +				member->offset;
> +
>  			if (btf_type_skip_modifiers(btf, member->type, &tid) &&
>  			    top < BTF_ANON_STACK_MAX) {
>  				anon_stack[top].tid = tid;
>  				anon_stack[top++].offset =
> -					cur_offset + member->offset;
> +					cur_offset + m_off;
>  			}
>  		} else {

[Severity: High]
This isn't a bug introduced by this patch, but is it possible for unnamed
bitfields to break nested anonymous struct resolution here?

Since unnamed bitfields (like int : 5) also have name_off == 0, they get
pushed onto anon_stack alongside actual anonymous structs.

Because anon_stack is processed in LIFO order, an unnamed bitfield defined
after an anonymous struct will be popped first. When it is popped at the top
of btf_find_struct_member():

retry:
	if (!btf_type_is_struct(type)) {
		member = ERR_PTR(-EINVAL);
		goto out;
	}

Does this cause the scalar type check to fail and abort the entire search,
preventing the earlier anonymous struct from ever being searched?

>  			name = btf_name_by_offset(btf, member->name_off);
>  			if (name && !strcmp(member_name, name)) {
>  				if (anon_offset)
>  					*anon_offset = cur_offset;

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/178810001186.64882.2161016469449127450.stgit@devnote2?part=2