Re: [PATCH] fix handling of zero length domain names in dn_expand

[Szabolcs Nagy <nsz@port70.net>]

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* Szabolcs Nagy <nsz@port70.net> [2014-09-04 19:07:27 +0200]:
> * Natanael Copa <ncopa@alpinelinux.org> [2014-09-04 09:50:39 +0200]:
> > Rich pointed out to me on IRC that this will not write terminating '\0'
> > when domain name length is zero. I'll send new patch.
> > 
> 
> here is a patch

another try

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From 1a068a048b64999f97add01ce8f5013a83b0e916 Mon Sep 17 00:00:00 2001
From: Szabolcs Nagy <nsz@port70.net>
Date: Thu, 4 Sep 2014 18:29:16 +0200
Subject: [PATCH] fix dn_expand empty name handling and offsets to 0

Empty name was rejected in dn_expand since commit
56b57f37a46dab432247bf29d96fcb11fbd02a6d
which is a regression as reported by Natanael Copa.

Furthermore if an offset pointer in a compressed name
pointed to a terminating 0 byte (instead of a label)
the returned name was not null terminated.
---
 src/network/dn_expand.c |   14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/src/network/dn_expand.c b/src/network/dn_expand.c
index 849df19..d1ebebf 100644
--- a/src/network/dn_expand.c
+++ b/src/network/dn_expand.c
@@ -5,8 +5,8 @@ int __dn_expand(const unsigned char *base, const unsigned char *end, const unsig
 {
 	const unsigned char *p = src;
 	char *dend = dest + (space > 254 ? 254 : space);
-	int len = -1, i, j;
-	if (p==end || !*p) return -1;
+	int len = -1, i, j, first = 1;
+	if (p==end || dest==dend) return -1;
 	/* detect reference loop using an iteration counter */
 	for (i=0; i < end-base; i+=2) {
 		if (*p & 0xc0) {
@@ -16,11 +16,13 @@ int __dn_expand(const unsigned char *base, const unsigned char *end, const unsig
 			if (j >= end-base) return -1;
 			p = base+j;
 		} else if (*p) {
-			j = *p+1;
-			if (j>=end-p || j>dend-dest) return -1;
-			while (--j) *dest++ = *++p;
-			*dest++ = *++p ? '.' : 0;
+			if (!first) *dest++ = '.';
+			first = 0;
+			j = *p++;
+			if (j >= end-p || j >= dend-dest) return -1;
+			while (j--) *dest++ = *p++;
 		} else {
+			*dest = 0;
 			if (len < 0) len = p+1-src;
 			return len;
 		}
-- 
1.7.10.4