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Check destination of DNS UDP query replies.

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At any time, dnsmasq will have a set of sockets open, bound to
random ports, on which it sends queries to upstream nameservers.
This patch fixes the existing problem that a reply for ANY in-flight
query would be accepted via ANY open port, which increases the
chances of an attacker flooding answers "in the blind" in an
attempt to poison the DNS cache. CERT VU#434904 refers.
This commit is contained in:
Simon Kelley
2020-11-12 18:49:23 +00:00
parent 4e96a4be68
commit 257ac0c5f7
2 changed files with 33 additions and 10 deletions
Download Patch File Download Diff File Expand all files Collapse all files

6
CHANGELOG
View File

@@ -6,8 +6,12 @@ version 2.83
dnsmasq with DNSSEC compiled in and enabled is vulnerable to this,
referenced by CERT VU#434904.
Be sure to only accept UDP DNS query replies at the address
from which the query was originated. This keeps as much entropy
in the {query-ID, random-port} tuple as possible, help defeat
cache poisoning attacks. Refer: CERT VU#434904.
>>>>>>> Fix remote buffer overflow CERT VU#434904
version 2.82
Improve behaviour in the face of network interfaces which come
and go and change index. Thanks to Petr Mensik for the patch.

35
src/forward.c
View File

@@ -16,7 +16,7 @@
#include "dnsmasq.h"
static struct frec *lookup_frec(unsigned short id, void *hash);
static struct frec *lookup_frec(unsigned short id, int fd, int family, void *hash);
static struct frec *lookup_frec_by_sender(unsigned short id,
union mysockaddr *addr,
void *hash);
@@ -805,7 +805,7 @@ void reply_query(int fd, int family, time_t now)
crc = questions_crc(header, n, daemon->namebuff);
#endif
if (!(forward = lookup_frec(ntohs(header->id), hash)))
if (!(forward = lookup_frec(ntohs(header->id), fd, family, hash)))
return;
#ifdef HAVE_DUMPFILE
@@ -2339,14 +2339,25 @@ struct frec *get_new_frec(time_t now, int *wait, struct frec *force)
}
/* crc is all-ones if not known. */
static struct frec *lookup_frec(unsigned short id, void *hash)
static struct frec *lookup_frec(unsigned short id, int fd, int family, void *hash)
{
struct frec *f;
for(f = daemon->frec_list; f; f = f->next)
if (f->sentto && f->new_id == id &&
(!hash || memcmp(hash, f->hash, HASH_SIZE) == 0))
return f;
{
/* sent from random port */
if (family == AF_INET && f->rfd4 && f->rfd4->fd == fd)
return f;
if (family == AF_INET6 && f->rfd6 && f->rfd6->fd == fd)
return f;
/* sent to upstream from bound socket. */
if (f->sentto->sfd && f->sentto->sfd->fd == fd)
return f;
}
return NULL;
}
@@ -2407,12 +2418,20 @@ void server_gone(struct server *server)
static unsigned short get_id(void)
{
unsigned short ret = 0;
struct frec *f;
do
ret = rand16();
while (lookup_frec(ret, NULL));
while (1)
{
ret = rand16();
return ret;
/* ensure id is unique. */
for (f = daemon->frec_list; f; f = f->next)
if (f->sentto && f->new_id == ret)
break;
if (!f)
return ret;
}
}