From: Roy Marples <roy@marples.name>
Date: Mon, 3 Jul 2023 12:11:05 +0000 (+0100)
Subject: common: Allow hwaddr_ntoa to print an empty string
X-Git-Tag: v9.5.2~2
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=c4f6e7d8f2b6cbbf6f0595779c9d3ca95352b86d;p=thirdparty%2Fdhcpcd.git

common: Allow hwaddr_ntoa to print an empty string

This fixes #218 where we get a zero hardware address length in
an ARP packet or a length that overflows the string buffer.
---

diff --git a/src/common.c b/src/common.c
index bb89100e..8eafe69e 100644
--- a/src/common.c
+++ b/src/common.c
@@ -46,10 +46,15 @@ hwaddr_ntoa(const void *hwaddr, size_t hwlen, char *buf, size_t buflen)
 	const unsigned char *hp, *ep;
 	char *p;
 
-	if (buf == NULL || hwlen == 0)
+	/* Allow a hwlen of 0 to be an empty string. */
+	if (buf == NULL || buflen == 0) {
+		errno = ENOBUFS;
 		return NULL;
+	}
 
 	if (hwlen * 3 > buflen) {
+		/* We should still terminate the string just in case. */
+		buf[0] = '\0';
 		errno = ENOBUFS;
 		return NULL;
 	}
@@ -57,7 +62,6 @@ hwaddr_ntoa(const void *hwaddr, size_t hwlen, char *buf, size_t buflen)
 	hp = hwaddr;
 	ep = hp + hwlen;
 	p = buf;
-
 	while (hp < ep) {
 		if (hp != hwaddr)
 			*p ++= ':';