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Bound the value of UDP packet size in the EDNS0 header of

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forwarded queries to the configured or default value of
edns-packet-max. There's no point letting a client set a larger
value if we're unable to return the answer.
This commit is contained in:
Bertie, Taylor
2022-07-31 17:20:21 +01:00
committed by Simon Kelley
parent 6134b94c02
commit 5586934da0
2 changed files with 12 additions and 2 deletions
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6
CHANGELOG
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@@ -65,6 +65,12 @@ version 2.87
The new feature allows configuration to provide bug-for-bug The new feature allows configuration to provide bug-for-bug
compatibility, if required. Thanks to Damian Kaczkowski compatibility, if required. Thanks to Damian Kaczkowski
for the feature suggestion. for the feature suggestion.
Bound the value of UDP packet size in the EDNS0 header of
forwarded queries to the configured or default value of
edns-packet-max. There's no point letting a client set a larger
value if we're unable to return the answer. Thanks to Bertie
Taylor for pointing out the problem and supplying the patch.
version 2.86 version 2.86

8
src/forward.c
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@@ -1619,13 +1619,17 @@ void receive_query(struct listener *listen, time_t now)
/* If the client provides an EDNS0 UDP size, use that to limit our reply. /* If the client provides an EDNS0 UDP size, use that to limit our reply.
(bounded by the maximum configured). If no EDNS0, then it (bounded by the maximum configured). If no EDNS0, then it
defaults to 512 */ defaults to 512. We write this value into the query packet too, so that
if it's forwarded, we don't specify a maximum size greater than we can handle. */
if (udp_size > daemon->edns_pktsz) if (udp_size > daemon->edns_pktsz)
udp_size = daemon->edns_pktsz; udp_size = daemon->edns_pktsz;
else if (udp_size < PACKETSZ) else if (udp_size < PACKETSZ)
udp_size = PACKETSZ; /* Sanity check - can't reduce below default. RFC 6891 6.2.3 */ udp_size = PACKETSZ; /* Sanity check - can't reduce below default. RFC 6891 6.2.3 */
}
pheader -= 6; /* ext_class */
PUTSHORT(udp_size, pheader); /* Bounding forwarded queries to maximum configured */
}
#ifdef HAVE_CONNTRACK #ifdef HAVE_CONNTRACK
#ifdef HAVE_AUTH #ifdef HAVE_AUTH
if (!auth_dns || local_auth) if (!auth_dns || local_auth)