From 897c113fda0886a28a986cc6ba17bb93bd6cb1c7 Mon Sep 17 00:00:00 2001 From: Simon Kelley Date: Mon, 25 Sep 2017 20:11:58 +0100 Subject: [PATCH] Security fix, CVE-2017-14496, Integer underflow in DNS response creation. Fix DoS in DNS. Invalid boundary checks in the add_pseudoheader function allows a memcpy call with negative size An attacker which can send malicious DNS queries to dnsmasq can trigger a DoS remotely. dnsmasq is vulnerable only if one of the following option is specified: --add-mac, --add-cpe-id or --add-subnet. --- src/edns0.c | 13 ++++++++++++- 1 file changed, 12 insertions(+), 1 deletion(-) diff --git a/src/edns0.c b/src/edns0.c index f5b798c..95b74ee 100644 --- a/src/edns0.c +++ b/src/edns0.c @@ -144,7 +144,7 @@ size_t add_pseudoheader(struct dns_header *header, size_t plen, unsigned char *l GETSHORT(len, p); /* malformed option, delete the whole OPT RR and start again. */ - if (i + len > rdlen) + if (i + 4 + len > rdlen) { rdlen = 0; is_last = 0; @@ -193,6 +193,8 @@ size_t add_pseudoheader(struct dns_header *header, size_t plen, unsigned char *l ntohs(header->ancount) + ntohs(header->nscount) + ntohs(header->arcount), header, plen))) return plen; + if (p + 11 > limit) + return plen; /* Too big */ *p++ = 0; /* empty name */ PUTSHORT(T_OPT, p); PUTSHORT(udp_sz, p); /* max packet length, 512 if not given in EDNS0 header */ @@ -204,6 +206,11 @@ size_t add_pseudoheader(struct dns_header *header, size_t plen, unsigned char *l /* Copy back any options */ if (buff) { + if (p + rdlen > limit) + { + free(buff); + return plen; /* Too big */ + } memcpy(p, buff, rdlen); free(buff); p += rdlen; @@ -220,8 +227,12 @@ size_t add_pseudoheader(struct dns_header *header, size_t plen, unsigned char *l /* Add new option */ if (optno != 0 && replace != 2) { + if (p + 4 > limit) + return plen; /* Too big */ PUTSHORT(optno, p); PUTSHORT(optlen, p); + if (p + optlen > limit) + return plen; /* Too big */ memcpy(p, opt, optlen); p += optlen; PUTSHORT(p - datap, lenp); -- 2.9.5