From: David Carlier Date: Fri, 8 May 2026 19:57:47 +0000 (+0100) Subject: tracing: Avoid NULL return from hist_field_name() on truncation X-Git-Tag: v6.12.92~16 X-Git-Url: http://git.ipfire.org/gitweb/index.cgi?a=commitdiff_plain;h=be4e99038c1603fa6b329d8ee3e364825e17c353;p=thirdparty%2Fkernel%2Fstable.git tracing: Avoid NULL return from hist_field_name() on truncation [ Upstream commit 576ec047d20b368b43c4d5db98c4f2e0f3c101ec ] hist_field_name() returns "" everywhere except the fully-qualified VAR_REF/EXPR case, where snprintf() truncation returns NULL early and bypasses the bottom NULL->"" guard. Callers don't expect NULL: strcat(expr, hist_field_name(field, 0)) at trace_events_hist.c:1758 and the strcmp() in the sort-key match loop at :4804 both deref it. system and event_name are bounded by MAX_EVENT_NAME_LEN, but the field name on a VAR_REF is kstrdup'd from a histogram variable name parsed out of the trigger string and has no length cap, so a long enough var name in a fully qualified reference can reach the truncation path. Keep the length check but leave field_name as "" on overflow. Link: https://patch.msgid.link/20260508195747.25492-1-devnexen@gmail.com Fixes: 5ec1d1e97de1 ("tracing: Rebuild full_name on each hist_field_name() call") Signed-off-by: David Carlier Signed-off-by: Steven Rostedt Signed-off-by: Sasha Levin --- diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c index 2d085115afde..2a1e3537332d 100644 --- a/kernel/trace/trace_events_hist.c +++ b/kernel/trace/trace_events_hist.c @@ -1347,10 +1347,8 @@ static const char *hist_field_name(struct hist_field *field, len = snprintf(full_name, sizeof(full_name), "%s.%s.%s", field->system, field->event_name, field->name); - if (len >= sizeof(full_name)) - return NULL; - - field_name = full_name; + if (len < sizeof(full_name)) + field_name = full_name; } else field_name = field->name; } else if (field->flags & HIST_FIELD_FL_TIMESTAMP)