On Tue, 06 Oct 2026 15:56:42 -0700, Kyle Zeng <[email protected]> wrote: > The regex callbacks use a length of zero for NUL-terminated strings of > unknown size, such as the trailing buffer in a trace_marker record. > However, filter_pred_strloc() and filter_pred_strrelloc() pass the length > from a data locator directly to those callbacks. A zero-length locator > has no data and need not point at a NUL byte. > > In particular, syscall entry events can contain an empty captured array > or a failed user-string copy. Matching such a field with an equality, > prefix, or substring filter can read beyond the record. The per-CPU perf > trace buffer is reused, so an unprivileged counting syscall event can > disclose bytes left by a previous kernel tracepoint even when raw > sampling is denied and exclude_kernel prevents counting that tracepoint. > > Handle both locator formats through a common helper. For a zero-length > field, pass an empty string and its actual size to the regex callback. > This gives all matching modes the empty-string semantics without reading > the locator's target. Keep nonzero fields and the legacy trace_marker > unknown-length convention unchanged. > > Fixes: 10f20e9f9da9 ("tracing: Have zero size length in filter logic be full > string") > Cc: [email protected] > Assisted-by: Codex:gpt-6-astra
nit: Assisted-by: LLM > Signed-off-by: Kyle Zeng <[email protected]> Looks good to me. Reviewed-by: Masami Hiramatsu (Google) <[email protected]> Thanks, > --- > kernel/trace/trace_events_filter.c | 38 +++++++++++++++++++----------- > 1 file changed, 24 insertions(+), 14 deletions(-) > > diff --git a/kernel/trace/trace_events_filter.c > b/kernel/trace/trace_events_filter.c > index 2b46ca536045..02aaa92e0361 100644 > --- a/kernel/trace/trace_events_filter.c > +++ b/kernel/trace/trace_events_filter.c > @@ -884,6 +884,25 @@ static int filter_pred_pchar_user(struct filter_pred > *pred, void *event) > return filter_pchar(pred, str); > } > > +static __always_inline int filter_dyn_string(struct filter_pred *pred, > + char *str, int len) > +{ > + int cmp; > + > + /* > + * The regex callbacks use zero for an unknown-length, NUL-terminated > + * string. A zero-length data_loc or rel_loc field has no bytes at all. > + * Match an empty string instead of reading past the end of the field. > + */ > + if (!len) { > + str = ""; > + len = 1; > + } > + > + cmp = pred->regex->match(str, pred->regex, len); > + return cmp ^ pred->not; > +} > + > /* > * Filter predicate for dynamic sized arrays of characters. > * These are implemented through a list of strings at the end > @@ -900,13 +919,8 @@ static int filter_pred_strloc(struct filter_pred *pred, > void *event) > int str_loc = str_item & 0xffff; > int str_len = str_item >> 16; > char *addr = (char *)(event + str_loc); > - int cmp, match; > - > - cmp = pred->regex->match(addr, pred->regex, str_len); > > - match = cmp ^ pred->not; > - > - return match; > + return filter_dyn_string(pred, addr, str_len); > } > > /* > @@ -923,13 +937,8 @@ static int filter_pred_strrelloc(struct filter_pred > *pred, void *event) > int str_loc = str_item & 0xffff; > int str_len = str_item >> 16; > char *addr = (char *)(&item[1]) + str_loc; > - int cmp, match; > - > - cmp = pred->regex->match(addr, pred->regex, str_len); > > - match = cmp ^ pred->not; > - > - return match; > + return filter_dyn_string(pred, addr, str_len); > } > > /* Filter predicate for CPUs. */ > @@ -1014,7 +1023,8 @@ static int filter_pred_function(struct filter_pred > *pred, void *event) > * > * @str: the string to be searched > * @r: the regex structure containing the pattern string > - * @len: the length of the string to be searched (including '\0') > + * @len: the length of the string to be searched (including '\0'), or zero > + * for a NUL-terminated string of unknown length > * > * Note: > * - @str might not be NULL-terminated if it's of type DYN_STRING > @@ -1023,7 +1033,7 @@ static int filter_pred_function(struct filter_pred > *pred, void *event) > > static int regex_match_full(char *str, struct regex *r, int len) > { > - /* len of zero means str is dynamic and ends with '\0' */ > + /* Zero is reserved for a NUL-terminated string of unknown length. */ > if (!len) > return strcmp(str, r->pattern) == 0; > > -- Masami Hiramatsu (Google) <[email protected]>
