On Sun, 25 Oct 2026 17:37:19 +0900, Masami Hiramatsu (Google) <[email protected]> wrote: > From: Masami Hiramatsu (Google) <[email protected]> > > regex_match_end() calculated string length as "len - 1", assuming @len is > the string length including trailing '\0'. However, for fixed-size string > fields, filter_pred_string() passes field->size as @len, and for "comm", > filter_pred_comm() passes TASK_COMM_LEN as @len. > > Because @len in these cases represents the buffer capacity rather than the > actual length of the string, regex_match_end() tests against the tail of > the buffer (typically trailing '\0' padding) rather than the end of the > string. Furthermore, if @len is 0 (denoting an empty dynamic array without > trailing '\0'), "len - 1" underflows to -1. > > First check "len < r->len" and return 0, which safely rejects negative > lengths and cases where the buffer capacity is smaller than the pattern. > Then compute the actual string length using strnlen(str, len), which > bounds the scan by @len (stopping at the first '\0') without dereferencing > past the buffer. > > Fixes: a3291c14ecf0 ("tracing/filters: Fix MATCH_END_ONLY filter matching") > Cc: [email protected] > Signed-off-by: Masami Hiramatsu (Google) <[email protected]> > --- > Changes in v2: > - Check "len < r->len" to guard against negative lengths and avoid > calling strnlen() when the buffer capacity is smaller than the pattern. > - Use strnlen(str, len) directly instead of calling strlen(str) when > len is 0, avoiding an out-of-bounds read on 0-length dynamic arrays. > --- > kernel/trace/trace_events_filter.c | 10 +++++++--- > 1 file changed, 7 insertions(+), 3 deletions(-) > > diff --git a/kernel/trace/trace_events_filter.c > b/kernel/trace/trace_events_filter.c > index 5e74d2dae40a..fac51a2953dd 100644 > --- a/kernel/trace/trace_events_filter.c > +++ b/kernel/trace/trace_events_filter.c > @@ -1075,10 +1075,14 @@ 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 slen; > > - if (strlen >= r->len && > - memcmp(str + strlen - r->len, r->pattern, r->len) == 0) > + if (len < r->len) > + return 0; > + > + slen = strnlen(str, len);
Hmm, this fixes 2 different issues. One is out-of-bound access issue (len == 0 case) and MATCH_END_ONLY for COMM/STATIC_STRING issue. For example, FILTER_COMM will pass the TASK_COMM_LEN as @len, thus "str + (len - 1)" points the end of comm array. Thus in most cases, the filter checks only the zero padding area. OK, let me split this into 2 patches. Thanks, > + if (slen >= r->len && > + memcmp(str + slen - r->len, r->pattern, r->len) == 0) > return 1; > return 0; > } > > -- Masami Hiramatsu (Google) <[email protected]>
