From b3d9e0b94ea73c68ef4169ec82c898ce59a4e30a Mon Sep 17 00:00:00 2001 From: Szabolcs Nagy Date: Thu, 5 Jun 2014 22:32:42 +0200 Subject: [PATCH] fix multiple validation issues in dns response label parsing Due to an error introduced in commit fcc522c92335783293ac19df318415cd97fbf66b, checking of the remaining output buffer space was not performed correctly, allowing malformed input to write past the end of the buffer. In addition, the loop detection logic failed to account for the possibility of infinite loops with no output, which would hang the function. The output size is now limited more strictly so only names with valid length are accepted. --- src/network/dn_expand.c | 10 ++++++---- 1 file changed, 6 insertions(+), 4 deletions(-) diff --git a/src/network/dn_expand.c b/src/network/dn_expand.c index 96adf37e..849df19a 100644 --- a/src/network/dn_expand.c +++ b/src/network/dn_expand.c @@ -4,10 +4,11 @@ int __dn_expand(const unsigned char *base, const unsigned char *end, const unsigned char *src, char *dest, int space) { const unsigned char *p = src; - int len = -1, j; - if (space > 256) space = 256; + char *dend = dest + (space > 254 ? 254 : space); + int len = -1, i, j; if (p==end || !*p) return -1; - for (;;) { + /* detect reference loop using an iteration counter */ + for (i=0; i < end-base; i+=2) { if (*p & 0xc0) { if (p+1==end) return -1; j = ((p[0] & 0x3f) << 8) | p[1]; @@ -16,7 +17,7 @@ int __dn_expand(const unsigned char *base, const unsigned char *end, const unsig p = base+j; } else if (*p) { j = *p+1; - if (j>=end-p || j>space) return -1; + if (j>=end-p || j>dend-dest) return -1; while (--j) *dest++ = *++p; *dest++ = *++p ? '.' : 0; } else { @@ -24,6 +25,7 @@ int __dn_expand(const unsigned char *base, const unsigned char *end, const unsig return len; } } + return -1; } weak_alias(__dn_expand, dn_expand); -- 2.25.1