From 28ece127aee19881956c55c7f704f60682034dc8 Mon Sep 17 00:00:00 2001
From: Bodo Petermann <b.petermann@syseleven.de>
Date: Mon, 17 Mar 2025 12:06:07 +0100
Subject: [PATCH] out_gelf: fix crash after missing short_message key

Fix for an illegal free in the gelf output plugin when it handled
a message lacking the short_message key.
In `cb_gelf_flush`: if the input doesn't contain the short_message key
`flb_msgpack_to_gelf` will fail and return NULL. The variable `s` is
not initialized, but still `flb_sds_destroy(s)` is called which
may unexpectedly free some arbitrary pointer.
Fixed by initializing `s`.

Fixes #10086
---
 plugins/out_gelf/gelf.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/plugins/out_gelf/gelf.c b/plugins/out_gelf/gelf.c
index 0499cddc157..1d18ba0305d 100644
--- a/plugins/out_gelf/gelf.c
+++ b/plugins/out_gelf/gelf.c
@@ -312,6 +312,7 @@ static void cb_gelf_flush(struct flb_event_chunk *event_chunk,
         off = log_decoder.offset;
         size = off - prev_off;
         prev_off = off;
+        s = NULL;
 
         map = *log_event.body;