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Fix bug #48924: Potential out of bound reads in DNS codes of lwip project by adding checks for pbuf_copy_partial() return values.

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Add some comments to clarify handling of untrusted network data handling.
This commit is contained in:
Dirk Ziegelmeier 2016-08-30 21:07:37 +02:00
parent 198fa5dbfa
commit 840d1e60fa
1 changed files with 18 additions and 4 deletions
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22
src/core/dns.c
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@ -640,6 +640,7 @@ dns_parse_name(struct pbuf* p, u16_t query_idx)
unsigned char n; unsigned char n;
do { do {
/* pbuf_get_at() returns 0 on out-of-bounds access, so we will terminate */
n = pbuf_get_at(p, query_idx++); n = pbuf_get_at(p, query_idx++);
/** @see RFC 1035 - 4.1.4. Message compression */ /** @see RFC 1035 - 4.1.4. Message compression */
if ((n & 0xc0) == 0xc0) { if ((n & 0xc0) == 0xc0) {
@ -652,6 +653,7 @@ dns_parse_name(struct pbuf* p, u16_t query_idx)
--n; --n;
} }
} }
/* pbuf_get_at() returns 0 on out-of-bounds access, so we will terminate */
} while (pbuf_get_at(p, query_idx) != 0); } while (pbuf_get_at(p, query_idx) != 0);
return query_idx + 1; return query_idx + 1;
@ -1096,7 +1098,9 @@ dns_recv(void *arg, struct udp_pcb *pcb, struct pbuf *p, const ip_addr_t *addr,
} }
/* check if "question" part matches the request */ /* check if "question" part matches the request */
pbuf_copy_partial(p, &qry, SIZEOF_DNS_QUERY, res_idx); if (pbuf_copy_partial(p, &qry, SIZEOF_DNS_QUERY, res_idx) != SIZEOF_DNS_QUERY) {
goto memerr; /* ignore this packet */
}
if ((qry.cls != PP_HTONS(DNS_RRCLASS_IN)) || if ((qry.cls != PP_HTONS(DNS_RRCLASS_IN)) ||
(LWIP_DNS_ADDRTYPE_IS_IPV6(entry->reqaddrtype) && (qry.type != PP_HTONS(DNS_RRTYPE_AAAA))) || (LWIP_DNS_ADDRTYPE_IS_IPV6(entry->reqaddrtype) && (qry.type != PP_HTONS(DNS_RRTYPE_AAAA))) ||
(!LWIP_DNS_ADDRTYPE_IS_IPV6(entry->reqaddrtype) && (qry.type != PP_HTONS(DNS_RRTYPE_A)))) { (!LWIP_DNS_ADDRTYPE_IS_IPV6(entry->reqaddrtype) && (qry.type != PP_HTONS(DNS_RRTYPE_A)))) {
@ -1113,10 +1117,16 @@ dns_recv(void *arg, struct udp_pcb *pcb, struct pbuf *p, const ip_addr_t *addr,
while ((nanswers > 0) && (res_idx < p->tot_len)) { while ((nanswers > 0) && (res_idx < p->tot_len)) {
/* skip answer resource record's host name */ /* skip answer resource record's host name */
res_idx = dns_parse_name(p, res_idx); res_idx = dns_parse_name(p, res_idx);
/* dns_parse_name() may return an res_idx out of pbuf bounds.
* This will be caught in pbuf_copy_partial() below.
*/
/* Check for IP address type and Internet class. Others are discarded. */ /* Check for IP address type and Internet class. Others are discarded. */
pbuf_copy_partial(p, &ans, SIZEOF_DNS_ANSWER, res_idx); if (pbuf_copy_partial(p, &ans, SIZEOF_DNS_ANSWER, res_idx) != SIZEOF_DNS_ANSWER) {
goto memerr; /* ignore this packet */
}
res_idx += SIZEOF_DNS_ANSWER; res_idx += SIZEOF_DNS_ANSWER;
if (ans.cls == PP_HTONS(DNS_RRCLASS_IN)) { if (ans.cls == PP_HTONS(DNS_RRCLASS_IN)) {
#if LWIP_IPV4 #if LWIP_IPV4
if ((ans.type == PP_HTONS(DNS_RRTYPE_A)) && (ans.len == PP_HTONS(sizeof(ip4_addr_t)))) { if ((ans.type == PP_HTONS(DNS_RRTYPE_A)) && (ans.len == PP_HTONS(sizeof(ip4_addr_t)))) {
@ -1126,7 +1136,9 @@ dns_recv(void *arg, struct udp_pcb *pcb, struct pbuf *p, const ip_addr_t *addr,
{ {
ip4_addr_t ip4addr; ip4_addr_t ip4addr;
/* read the IP address after answer resource record's header */ /* read the IP address after answer resource record's header */
pbuf_copy_partial(p, &ip4addr, sizeof(ip4_addr_t), res_idx); if (pbuf_copy_partial(p, &ip4addr, sizeof(ip4_addr_t), res_idx) != sizeof(ip4_addr_t)) {
goto memerr; /* ignore this packet */
}
ip_addr_copy_from_ip4(dns_table[i].ipaddr, ip4addr); ip_addr_copy_from_ip4(dns_table[i].ipaddr, ip4addr);
pbuf_free(p); pbuf_free(p);
/* handle correct response */ /* handle correct response */
@ -1143,7 +1155,9 @@ dns_recv(void *arg, struct udp_pcb *pcb, struct pbuf *p, const ip_addr_t *addr,
{ {
ip6_addr_t ip6addr; ip6_addr_t ip6addr;
/* read the IP address after answer resource record's header */ /* read the IP address after answer resource record's header */
pbuf_copy_partial(p, &ip6addr, sizeof(ip6_addr_t), res_idx); if (pbuf_copy_partial(p, &ip6addr, sizeof(ip6_addr_t), res_idx) != sizeof(ip6_addr_t)) {
goto memerr; /* ignore this packet */
}
ip_addr_copy_from_ip6(dns_table[i].ipaddr, ip6addr); ip_addr_copy_from_ip6(dns_table[i].ipaddr, ip6addr);
pbuf_free(p); pbuf_free(p);
/* handle correct response */ /* handle correct response */