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- From 122392e0b352507cabb9e982208d35d2e56902e0 Mon Sep 17 00:00:00 2001
- From: Simon Kelley <simon@thekelleys.org.uk>
- Date: Wed, 31 Oct 2018 22:24:02 +0000
- Subject: [PATCH 09/32] Revert 68f6312d4bae30b78daafcd6f51dc441b8685b1e
- The above is intended to increase robustness, but actually does the
- opposite. The problem is that by ignoring SERVFAIL messages and hoping
- for a better answer from another of the servers we've forwarded to,
- we become vulnerable in the case that one or more of the configured
- servers is down or not responding.
- Consider the case that a domain is indeed BOGUS, and we've send the
- query to n servers. With 68f6312d4bae30b78daafcd6f51dc441b8685b1e
- we ignore the first n-1 SERVFAIL replies, and only return the
- final n'th answer to the client. Now, if one of the servers we are
- forwarding to is down, then we won't get all n replies, and the
- client will never get an answer! This is a far more likely scenario
- than a temporary SERVFAIL from only one of a set of notionally identical
- servers, so, on the ground of robustness, we have to believe
- any SERVFAIL answers we get, and return them to the client.
- The client could be using the same recursive servers we are,
- so it should, in theory, retry on SERVFAIL anyway.
- Signed-off-by: Kevin Darbyshire-Bryant <ldir@darbyshire-bryant.me.uk>
- ---
- src/forward.c | 3 +--
- 1 file changed, 1 insertion(+), 2 deletions(-)
- --- a/src/forward.c
- +++ b/src/forward.c
- @@ -957,8 +957,7 @@ void reply_query(int fd, int family, tim
- we get a good reply from another server. Kill it when we've
- had replies from all to avoid filling the forwarding table when
- everything is broken */
- - if (forward->forwardall == 0 || --forward->forwardall == 1 ||
- - (RCODE(header) != REFUSED && RCODE(header) != SERVFAIL))
- + if (forward->forwardall == 0 || --forward->forwardall == 1 || RCODE(header) != REFUSED)
- {
- int check_rebind = 0, no_cache_dnssec = 0, cache_secure = 0, bogusanswer = 0;
-
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