On Wed, 28 Oct 2026 01:05:18 +0000, [email protected]
<[email protected]> wrote:
> Thank you for your contribution! Sashiko AI review found 1 potential issue(s)
> to consider:
> - [Medium] tracing/filters: unhandled zero len in regex_match_end_str()
> --
>
> commit 92251abf42afdb93bef9298fec46088f078a4aa8
> Author: Masami Hiramatsu (Google) <[email protected]>
>
> tracing/filters: Fix MATCH_END_ONLY regex matching for fixed-size strings
>
> This commit introduces regex_match_end_str() to handle suffix regex matching
> on fixed-size string buffers using strnlen(), and assigns it in parse_pred()
> for comm and static string fields.
>
> > diff --git a/kernel/trace/trace_events_filter.c
> > b/kernel/trace/trace_events_filter.c
> > index 59a0d3ba72740..f7c067a58ba41 100644
> > --- a/kernel/trace/trace_events_filter.c
> > +++ b/kernel/trace/trace_events_filter.c
> > @@ -1087,6 +1087,20 @@ static int regex_match_end(char *str, struct regex
> > *r, int len)
> > return 0;
> > }
> >
> > +static int regex_match_end_str(char *str, struct regex *r, int len)
> > +{
> > + int slen;
> > +
> > + if (len < r->len)
> > + return 0;
> > +
> > + slen = strnlen(str, len);
> > + if (slen >= r->len &&
> > + memcmp(str + slen - r->len, r->pattern, r->len) == 0)
> > + return 1;
> > + return 0;
> > +}
>
> [Severity: Medium]
> How does regex_match_end_str() behave when len is 0?
>
> For the ftrace/print event, the buf field is defined in
> kernel/trace/trace_export.c with a size of 0:
>
> #undef __dynamic_array
> #define __dynamic_array(_type, _item) {
> \
> .type = #_type "[]", .name = #_item, \
> .size = 0, .align = __alignof__(_type), \
> is_signed_type(_type), .filter_type = FILTER_OTHER },
>
> Because its type is "char[]", filter_assign_type() classifies it as a static
> string field while field->size remains 0. In parse_pred(),
> pred->regex->field_len is set to field->size (0) and pred->regex->match is
> set to regex_match_end_str():
>
> } else if (field->filter_type == FILTER_STATIC_STRING) {
> pred->fn_num = FILTER_PRED_FN_STRING;
> pred->regex->field_len = field->size;
> if (pred->regex->match == regex_match_end)
> pred->regex->match = regex_match_end_str;
>
> When a trigger or eprobe with a suffix filter (such as buf ~ "*foo") is
> evaluated via write_marker_to_buffer() -> event_triggers_call() ->
> filter_match_preds() -> filter_pred_string(), regex_match_end_str() is called
> with len == 0.
Good catch... this may be yet another issue.
I think we need another different set of matching functions for dynamic
string. Sharing it with static string (where len = 0 means zero length)
and dynamic string (where len = 0 means variable length string) is
a bad idea.
>
> As noted in the comment above regex_match_full() (added in commit
> 10f20e9f9da9 ("tracing: Have zero size length in filter logic be full
> string")), a len of zero indicates that str is a NUL-terminated string, which
> regex_match_full(), regex_match_front(), and regex_match_middle() handle
> explicitly:
>
> static int regex_match_full(char *str, struct regex *r, int len)
> {
> /* len of zero means str is dynamic and ends with '\0' */
> if (!len)
> return strcmp(str, r->pattern) == 0;
>
> In regex_match_end_str(), however, when len is 0, the (len < r->len) check
> returns 0 for any non-empty pattern, and strnlen(str, 0) also returns 0.
>
> Should regex_match_end_str() check for !len and use strlen(str) in that case,
> so that suffix filters on ftrace/print work as expected?
I rather like to have regex_match_end_dynstr() in this case.
Anyway, we should have a unit test for filters.
Thanks,
--
Masami Hiramatsu (Google) <[email protected]>
