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[188.141.5.72]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-48e6db171c9sm6526355e9.30.2026.05.08.12.57.49 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 08 May 2026 12:57:50 -0700 (PDT) From: David Carlier To: linux-trace-kernel@vger.kernel.org Cc: rostedt@goodmis.org, mhiramat@kernel.org, mathieu.desnoyers@efficios.com, zanussi@kernel.org, pengpeng@iscas.ac.cn, linux-kernel@vger.kernel.org, David Carlier Subject: [PATCH] tracing: Avoid NULL return from hist_field_name() on truncation Date: Fri, 8 May 2026 20:57:47 +0100 Message-ID: <20260508195747.25492-1-devnexen@gmail.com> X-Mailer: git-send-email 2.53.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 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. Fixes: 5ec1d1e97de1 ("tracing: Rebuild full_name on each hist_field_name() call") Signed-off-by: David Carlier --- kernel/trace/trace_events_hist.c | 6 ++---- 1 file changed, 2 insertions(+), 4 deletions(-) diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c index 0dbbf6cca9bc..eb2c2bc8bc3d 100644 --- a/kernel/trace/trace_events_hist.c +++ b/kernel/trace/trace_events_hist.c @@ -1369,10 +1369,8 @@ static const char *hist_field_name(struct hist_field *field, len = snprintf(full_name, sizeof(full_name), fmt, 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) -- 2.53.0