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Security fix, CVE-2017-14496, Integer underflow in DNS response creation.

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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.
This commit is contained in:
Simon Kelley
2017-09-25 20:11:58 +01:00
parent 33e3f1029c
commit 897c113fda
2 changed files with 23 additions and 1 deletions
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13
src/edns0.c
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@@ -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);