From 8e4795842317663aabac3cda1ec6e7f7844e31c6 Mon Sep 17 00:00:00 2001
From: Lennart Poettering <lennart@poettering.net>
Date: Mon, 25 Sep 2023 19:06:06 +0200
Subject: [PATCH] string-util: make strgrowpad0() a bit safer

Let#s make sure we never shorten the allocation leaving an invalid
string (i.e. a memory allocation without a trailing NUL) around.
---
 src/basic/string-util.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/src/basic/string-util.c b/src/basic/string-util.c
index 854cf963acb..7329bfacdf0 100644
--- a/src/basic/string-util.c
+++ b/src/basic/string-util.c
@@ -627,14 +627,23 @@ char* strshorten(char *s, size_t l) {
 }
 
 int strgrowpad0(char **s, size_t l) {
+        size_t sz;
+
         assert(s);
 
+        if (*s) {
+                sz = strlen(*s) + 1;
+                if (sz >= l) /* never shrink */
+                        return 0;
+        } else
+                sz = 0;
+
         char *q = realloc(*s, l);
         if (!q)
                 return -ENOMEM;
+
         *s = q;
 
-        size_t sz = strlen(*s);
         memzero(*s + sz, l - sz);
         return 0;
 }
-- 
2.47.3