On Mon, 26 Oct 2026 09:54:41 -0400, Steven Rostedt [off-list ref] wrote:
On Sun, 25 Oct 2026 01:25:33 +0900
"Masami Hiramatsu (Google)" [off-list ref] wrote:
quoted
From: Masami Hiramatsu (Google) <mhiramat@kernel.org>
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 a dynamic string ending with
'\0'), "len - 1" underflows to -1 and never matches.
Compute the actual string length using strnlen(str, len) when @len is
non-zero, and strlen(str) when @len is zero.
Fixes: a3291c14ecf0 ("tracing/filters: Fix MATCH_END_ONLY filter matching")
Cc: <redacted>
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
---
kernel/trace/trace_events_filter.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/kernel/trace/trace_events_filter.c b/kernel/trace/trace_events_filter.c
index 5e74d2dae40a..18ce3ec00d34 100644
--- a/kernel/trace/trace_events_filter.c
+++ b/kernel/trace/trace_events_filter.c
@@ -1075,10 +1075,10 @@ 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 = len ? strnlen(str, len) : strlen(str);
- if (strlen >= r->len &&
- memcmp(str + strlen - r->len, r->pattern, r->len) == 0)
+ if (slen >= r->len &&
+ memcmp(str + slen - r->len, r->pattern, r->len) == 0)
return 1;
This slows down the code as it adds more strlen() calculations (it could
have already been done.
I sent v2 already, which is slightly lighter (but still using strnlen)
https://lore.kernel.org/all/179291743946.492959.9624495647021680807.stgit@devnote2/ (local)
(anyway, 3/10 is already fixed as Sashiko mentioned.)
Let's fix the callers instead and have them pass in the real length.
OK, let me check it.
Thanks,
--
Masami Hiramatsu (Google) [off-list ref]