Previously, we hashed the question and combined it with the original
txid which was useful when concurrent queries were multiplexed on a
single local source port. We encountered some situations where the DNS
server canonicalizes the question in the response (uppercase converted
to lowercase in this case), which resulted in responses that we couldn't
match to the original request due to hash mismatches. This includes a
new test to cover that situation.
Fixes#2597
Signed-off-by: Adrian Dewhurst <adrian@tailscale.com>
This change (subject to some limitations) looks for the EDNS OPT record
in queries and responses, clamping the size field to fit within our DNS
receive buffer. If the size field is smaller than the DNS receive buffer
then it is left unchanged.
I think we will eventually need to transition to fully processing the
DNS queries to handle all situations, but this should cover the most
common case.
Mostly fixes#2066
Signed-off-by: Adrian Dewhurst <adrian@tailscale.com>
This raises the maximum DNS response message size from 512 to 4095. This
should be large enough for almost all situations that do not need TCP.
We still do not recognize EDNS, so we will still forward requests that
claim support for a larger response size than 4095 (that will be solved
later). For now, when a response comes back that is too large to fit in
our receive buffer, we now set the truncation flag in the DNS header,
which is an improvement from before but will prompt attempts to use TCP
which isn't supported yet.
On Windows, WSARecvFrom into a buffer that's too small returns an error
in addition to the data. On other OSes, the extra data is silently
discarded. In this case, we prefer the latter so need to catch the error
on Windows.
Partially addresses #1123
Signed-off-by: Adrian Dewhurst <adrian@tailscale.com>
Brad Fitzpatrick
Josh Bleecher Snyder
nicksherron
Adrian Dewhurst
David Anderson
Dmytro Shynkevych