From 445282d13b90712ef90d2c2141d0e19bb1d896d2 Mon Sep 17 00:00:00 2001 From: Simon Kelley Date: Mon, 25 Sep 2017 18:17:11 +0100 Subject: [PATCH] Security fix, CVE-2017-14491 DNS heap buffer overflow. Fix heap overflow in DNS code. This is a potentially serious security hole. It allows an attacker who can make DNS requests to dnsmasq, and who controls the contents of a domain, which is thereby queried, to overflow (by 2 bytes) a heap buffer and either crash, or even take control of, dnsmasq. (original commit 0549c73b7ea6b22a3c49beb4d432f185a81efcbc) --- src/dnsmasq.h | 2 +- src/dnssec.c | 2 +- src/option.c | 2 +- src/rfc1035.c | 50 +++++++++++++++++++++++++++++++++++++++++--------- src/rfc2131.c | 4 ++-- src/rfc3315.c | 4 ++-- src/util.c | 7 ++++++- 7 files changed, 54 insertions(+), 17 deletions(-) diff --git a/src/dnsmasq.h b/src/dnsmasq.h index 06fae35..7a18898 100644 --- a/src/dnsmasq.h +++ b/src/dnsmasq.h @@ -1179,7 +1179,7 @@ u32 rand32(void); u64 rand64(void); int legal_hostname(char *c); char *canonicalise(char *s, int *nomem); -unsigned char *do_rfc1035_name(unsigned char *p, char *sval); +unsigned char *do_rfc1035_name(unsigned char *p, char *sval, char *limit); void *safe_malloc(size_t size); void safe_pipe(int *fd, int read_noblock); void *whine_malloc(size_t size); diff --git a/src/dnssec.c b/src/dnssec.c index 3330eef..b6cb55f 100644 --- a/src/dnssec.c +++ b/src/dnssec.c @@ -2230,7 +2230,7 @@ size_t dnssec_generate_query(struct dns_header *header, unsigned char *end, char p = (unsigned char *)(header+1); - p = do_rfc1035_name(p, name); + p = do_rfc1035_name(p, name, NULL); *p++ = 0; PUTSHORT(type, p); PUTSHORT(class, p); diff --git a/src/option.c b/src/option.c index 064ef62..22bd19a 100644 --- a/src/option.c +++ b/src/option.c @@ -1415,7 +1415,7 @@ static int parse_dhcp_opt(char *errstr, char *arg, int flags) } p = newp; - end = do_rfc1035_name(p + len, dom); + end = do_rfc1035_name(p + len, dom, NULL); *end++ = 0; len = end - p; free(dom); diff --git a/src/rfc1035.c b/src/rfc1035.c index 1671883..3397a26 100644 --- a/src/rfc1035.c +++ b/src/rfc1035.c @@ -1062,6 +1062,7 @@ int check_for_ignored_address(struct dns_header *header, size_t qlen, struct bog return 0; } + int add_resource_record(struct dns_header *header, char *limit, int *truncp, int nameoffset, unsigned char **pp, unsigned long ttl, int *offset, unsigned short type, unsigned short class, char *format, ...) { @@ -1071,12 +1072,21 @@ int add_resource_record(struct dns_header *header, char *limit, int *truncp, int unsigned short usval; long lval; char *sval; +#define CHECK_LIMIT(size) \ + if (limit && p + (size) > (unsigned char*)limit) \ + { \ + va_end(ap); \ + goto truncated; \ + } if (truncp && *truncp) return 0; - + va_start(ap, format); /* make ap point to 1st unamed argument */ - + + /* nameoffset (1 or 2) + type (2) + class (2) + ttl (4) + 0 (2) */ + CHECK_LIMIT(12); + if (nameoffset > 0) { PUTSHORT(nameoffset | 0xc000, p); @@ -1085,7 +1095,13 @@ int add_resource_record(struct dns_header *header, char *limit, int *truncp, int { char *name = va_arg(ap, char *); if (name) - p = do_rfc1035_name(p, name); + p = do_rfc1035_name(p, name, limit); + if (!p) + { + va_end(ap); + goto truncated; + } + if (nameoffset < 0) { PUTSHORT(-nameoffset | 0xc000, p); @@ -1106,6 +1122,7 @@ int add_resource_record(struct dns_header *header, char *limit, int *truncp, int { #ifdef HAVE_IPV6 case '6': + CHECK_LIMIT(IN6ADDRSZ); sval = va_arg(ap, char *); memcpy(p, sval, IN6ADDRSZ); p += IN6ADDRSZ; @@ -1113,36 +1130,47 @@ int add_resource_record(struct dns_header *header, char *limit, int *truncp, int #endif case '4': + CHECK_LIMIT(INADDRSZ); sval = va_arg(ap, char *); memcpy(p, sval, INADDRSZ); p += INADDRSZ; break; case 'b': + CHECK_LIMIT(1); usval = va_arg(ap, int); *p++ = usval; break; case 's': + CHECK_LIMIT(2); usval = va_arg(ap, int); PUTSHORT(usval, p); break; case 'l': + CHECK_LIMIT(4); lval = va_arg(ap, long); PUTLONG(lval, p); break; case 'd': - /* get domain-name answer arg and store it in RDATA field */ - if (offset) - *offset = p - (unsigned char *)header; - p = do_rfc1035_name(p, va_arg(ap, char *)); - *p++ = 0; + /* get domain-name answer arg and store it in RDATA field */ + if (offset) + *offset = p - (unsigned char *)header; + p = do_rfc1035_name(p, va_arg(ap, char *), limit); + if (!p) + { + va_end(ap); + goto truncated; + } + CHECK_LIMIT(1); + *p++ = 0; break; case 't': usval = va_arg(ap, int); + CHECK_LIMIT(usval); sval = va_arg(ap, char *); if (usval != 0) memcpy(p, sval, usval); @@ -1154,20 +1182,24 @@ int add_resource_record(struct dns_header *header, char *limit, int *truncp, int usval = sval ? strlen(sval) : 0; if (usval > 255) usval = 255; + CHECK_LIMIT(usval + 1); *p++ = (unsigned char)usval; memcpy(p, sval, usval); p += usval; break; } +#undef CHECK_LIMIT va_end(ap); /* clean up variable argument pointer */ j = p - sav - 2; - PUTSHORT(j, sav); /* Now, store real RDLength */ + /* this has already been checked against limit before */ + PUTSHORT(j, sav); /* Now, store real RDLength */ /* check for overflow of buffer */ if (limit && ((unsigned char *)limit - p) < 0) { +truncated: if (truncp) *truncp = 1; return 0; diff --git a/src/rfc2131.c b/src/rfc2131.c index a679470..052498c 100644 --- a/src/rfc2131.c +++ b/src/rfc2131.c @@ -2454,10 +2454,10 @@ static void do_options(struct dhcp_context *context, if (fqdn_flags & 0x04) { - p = do_rfc1035_name(p, hostname); + p = do_rfc1035_name(p, hostname, NULL); if (domain) { - p = do_rfc1035_name(p, domain); + p = do_rfc1035_name(p, domain, NULL); *p++ = 0; } } diff --git a/src/rfc3315.c b/src/rfc3315.c index 054ecd0..715b6db 100644 --- a/src/rfc3315.c +++ b/src/rfc3315.c @@ -1479,10 +1479,10 @@ static struct dhcp_netid *add_options(struct state *state, int do_refresh) if ((p = expand(len + 2))) { *(p++) = state->fqdn_flags; - p = do_rfc1035_name(p, state->hostname); + p = do_rfc1035_name(p, state->hostname, NULL); if (state->send_domain) { - p = do_rfc1035_name(p, state->send_domain); + p = do_rfc1035_name(p, state->send_domain, NULL); *p = 0; } } diff --git a/src/util.c b/src/util.c index 145e53a..471faa9 100644 --- a/src/util.c +++ b/src/util.c @@ -227,15 +227,20 @@ char *canonicalise(char *in, int *nomem) return ret; } -unsigned char *do_rfc1035_name(unsigned char *p, char *sval) +unsigned char *do_rfc1035_name(unsigned char *p, char *sval, char *limit) { int j; while (sval && *sval) { + if (limit && p + 1 > (unsigned char*)limit) + return p; + unsigned char *cp = p++; for (j = 0; *sval && (*sval != '.'); sval++, j++) { + if (limit && p + 1 > (unsigned char*)limit) + return p; #ifdef HAVE_DNSSEC if (option_bool(OPT_DNSSEC_VALID) && *sval == NAME_ESCAPE) *p++ = (*(++sval))-1; -- 2.9.5