From: Tobias Stoeckmann <tobias@stoeckmann.org>
Date: Thu, 3 Mar 2022 20:18:53 +0000 (+0100)
Subject: printbuf_memset(): set gaps to zero
X-Git-Tag: json-c-0.16-20220414~15^2
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=refs%2Fpull%2F750%2Fhead;p=thirdparty%2Fjson-c.git

printbuf_memset(): set gaps to zero

It is possible to have a printbuf with "gaps", i.e. areas within the
print buffer which have not been initialized by using printbuf_memset.

Always clear memory in such cases.

Example:
```
struct printbuf *pb = printbuf_new();
printbuf_memset(pb, 10, 'a', 2);
```
In this case pb->buf[0] is '\0' but pb->buf[1] up to pb->buf[9] are
not set. The length would be 12 due to successful printbuf_memset.
---

diff --git a/printbuf.c b/printbuf.c
index 00822fac..716698ca 100644
--- a/printbuf.c
+++ b/printbuf.c
@@ -120,6 +120,8 @@ int printbuf_memset(struct printbuf *pb, int offset, int charvalue, int len)
 			return -1;
 	}
 
+	if (pb->bpos < offset)
+		memset(pb->buf + pb->bpos, '\0', offset - pb->bpos);
 	memset(pb->buf + offset, charvalue, len);
 	if (pb->bpos < size_needed)
 		pb->bpos = size_needed;