# Re: \[PATCH v3 01/16\] tracing/filters: Fix regex\_match\_end() for zero-length strings

- From: Masami Hiramatsu (Google) \<mhiramat@kernel.org\>
- Date: 2026-10-28 01:10:29 
- List: linux-trace-kernel
- Page: https://ratatoskr.run/linux-trace-kernel/2026/10/17814094
- Thread: https://ratatoskr.run/linux-trace-kernel/2026/10/17814009/t.md

```text
On Wed, 28 Oct 2026 00:59:33 +0000, sashiko-bot@kernel.org [ref] wrote:
> Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
> - [Medium] tracing/filters: redundant check in regex_match_end() makes patch a no-op
> --
> 
> commit 8e400c22f46c7fff9d91b8c8e837ab24dfa0f5cd
> Author: Masami Hiramatsu (Google) [ref]
> 
> tracing/filters: Fix regex_match_end() for zero-length strings
> 
> This commit adds an early return in regex_match_end() when len <= r->len to
> avoid underflowing len - 1 and accessing the input string when len is 0 or
> smaller than the pattern.

> 
> > diff --git a/kernel/trace/trace_events_filter.c b/kernel/trace/trace_events_filter.c
> > index 5e74d2dae40a3..59a0d3ba72740 100644
> > --- a/kernel/trace/trace_events_filter.c
> > +++ b/kernel/trace/trace_events_filter.c
> > @@ -1075,8 +1075,12 @@ static int regex_match_middle(char *str, struct regex *r, int len)
> >  
> >  static int regex_match_end(char *str, struct regex *r, int len)
> >  {
> > -	int strlen = len - 1;
> > +	int strlen;
> >  
> > +	if (len <= r->len)
> > +		return 0;
> > +
> > +	strlen = len - 1;
> >  	if (strlen >= r->len &&
> >  	    memcmp(str + strlen - r->len, r->pattern, r->len) == 0)
> >  		return 1;
> 
> [Severity: Medium]
> Does this change have any functional effect in regex_match_end() in
> kernel/trace/trace_events_filter.c?

Oops, right. Please drop this patch. This is my fault (I suggested).

> > +	if (len <= r->len)

and

> >  	if (strlen >= r->len &&

are the same...

Thanks!

-- 
Masami Hiramatsu (Google) [ref]
```