On Mon, May 4, 2026 at 8:42 AM Athira Rajeev <[email protected]> wrote: > > Replace snprintf with scnprintf in buffer offset calculations to > ensure the 'used' count will not exceed the "len". > > The current logic in perf_pmu__for_each_event uses an unconditional > + 1 increment to buf_used to account for null terminators. This can > cause a a stack buffer overflow in the subsequent scnprintf call. > When the local stack buffer buf (1024 bytes) is full, buf_used can > reach 1025. This causes the subsequent remaining space calculation > sizeof(buf) - buf_used to underflow. > > Use sub_non_neg() to see if space actually existed, and only > increment the offset if remaning space is present. > > Changes includes: > - Use sub_non_neg to check if space exists > - Replacing snprintf with scnprintf to ensure the return value > reflects the actual bytes written into the buffer. > - Only increment buf_used by 1 if space exists > - If a parameterized event uses a built-in perf keyword for its > parameter name (eg, config=?), the lexer parses it as a predefined > term token, which sets term->config to NULL. Add check to use > parse_events__term_type_str() if term->config is NULL. > > Signed-off-by: Athira Rajeev <[email protected]>
Reviewed-by: Ian Rogers <[email protected]> Thanks, Ian > --- > Changelog: > v2 -> v3: > - Split the scnprintf related changes in separate patch > - Handle the overflow issues and unconditional increment > wrapped around sub_non_neg addressing review comment from Sashiko > > tools/perf/util/pmu.c | 46 ++++++++++++++++++++++++++++++++----------- > 1 file changed, 35 insertions(+), 11 deletions(-) > > diff --git a/tools/perf/util/pmu.c b/tools/perf/util/pmu.c > index 0b8d58543f17..4b9ade1a4cf9 100644 > --- a/tools/perf/util/pmu.c > +++ b/tools/perf/util/pmu.c > @@ -2129,15 +2129,19 @@ static char *format_alias(char *buf, int len, const > struct perf_pmu *pmu, > pr_err("Failure to parse '%s' terms '%s': %d\n", > alias->name, alias->terms, ret); > parse_events_terms__exit(&terms); > - snprintf(buf, len, "%.*s/%s/", (int)pmu_name_len, pmu->name, > alias->name); > + scnprintf(buf, len, "%.*s/%s/", (int)pmu_name_len, pmu->name, > alias->name); > return buf; > } > - used = snprintf(buf, len, "%.*s/%s", (int)pmu_name_len, pmu->name, > alias->name); > + used = scnprintf(buf, len, "%.*s/%s", (int)pmu_name_len, pmu->name, > alias->name); > > list_for_each_entry(term, &terms.terms, list) { > + const char *name = term->config; > + > + if (!name) > + name = parse_events__term_type_str(term->type_term); > if (term->type_val == PARSE_EVENTS__TERM_TYPE_STR) > - used += snprintf(buf + used, sub_non_neg(len, used), > - ",%s=%s", term->config, > + used += scnprintf(buf + used, sub_non_neg(len, used), > + ",%s=%s", name, > term->val.str); > } > parse_events_terms__exit(&terms); > @@ -2201,6 +2205,7 @@ int perf_pmu__for_each_event(struct perf_pmu *pmu, bool > skip_duplicate_pmus, > int ret = 0; > struct hashmap_entry *entry; > size_t bkt; > + size_t size_rem, len; > > if (perf_pmu__is_tracepoint(pmu)) > return tp_pmu__for_each_event(pmu, state, cb); > @@ -2234,17 +2239,36 @@ int perf_pmu__for_each_event(struct perf_pmu *pmu, > bool skip_duplicate_pmus, > } > buf_used = strlen(buf) + 1; > } > + > info.scale_unit = NULL; > if (strlen(event->unit) || event->scale != 1.0) { > - info.scale_unit = buf + buf_used; > - buf_used += snprintf(buf + buf_used, sizeof(buf) - > buf_used, > - "%G%s", event->scale, event->unit) + > 1; > + /* Check the remaining space */ > + size_rem = sub_non_neg(sizeof(buf), buf_used); > + > + if (size_rem > 0) { > + info.scale_unit = buf + buf_used; > + len = scnprintf(buf + buf_used, size_rem, > "%G%s", > + event->scale, event->unit); > + /* > + * Increment buf_used by 1 only if > + * it fits remaining space > + */ > + buf_used += min(len + 1, size_rem); > + } > } > info.desc = event->desc; > info.long_desc = event->long_desc; > - info.encoding_desc = buf + buf_used; > - buf_used += snprintf(buf + buf_used, sizeof(buf) - buf_used, > - "%.*s/%s/", (int)pmu_name_len, info.pmu_name, > event->terms) + 1; > + info.encoding_desc = NULL; > + > + /* Check the remaining space */ > + size_rem = sub_non_neg(sizeof(buf), buf_used); > + if (size_rem > 0) { > + info.encoding_desc = buf + buf_used; > + len = scnprintf(buf + buf_used, size_rem, "%.*s/%s/", > + (int)pmu_name_len, info.pmu_name, > event->terms); > + buf_used += min(len + 1, size_rem); > + } > + > info.str = event->terms; > info.topic = event->topic; > info.deprecated = perf_pmu_alias__check_deprecated(pmu, > event); > @@ -2254,7 +2278,7 @@ int perf_pmu__for_each_event(struct perf_pmu *pmu, bool > skip_duplicate_pmus, > } > if (pmu->selectable) { > info.name = buf; > - snprintf(buf, sizeof(buf), "%s//", pmu->name); > + scnprintf(buf, sizeof(buf), "%s//", pmu->name); > info.alias = NULL; > info.scale_unit = NULL; > info.desc = NULL; > -- > 2.47.3 >
