When racing multiple upstream DNS resolvers, a REFUSED (RCode 5) response
from a broken or misconfigured resolver could win the race and be returned
to the client before healthier resolvers had a chance to respond with a
valid answer. This caused complete DNS failure in cases where, e.g., a
broken upstream resolver returned REFUSED quickly while a working resolver
(such as 1.1.1.1) was still responding.
Previously, only SERVFAIL (RCode 2) was treated as a soft error. REFUSED
responses were returned as successful bytes and could win the race
immediately. This change also treats REFUSED as a soft error in the UDP
and TCP forwarding paths, so the race continues until a better answer
arrives. If all resolvers refuse, the first REFUSED response is returned
to the client.
Additionally, SERVFAIL responses from upstream resolvers are now returned
verbatim to the client rather than replaced with a locally synthesized
packet. Synthesized SERVFAIL responses were authoritative and guaranteed
to include a question section echoing the original query; upstream
responses carry no such guarantees but may include extended error
information (e.g. RFC 8914 extended DNS errors) that would otherwise
be lost.
Fixes#19024
Signed-off-by: Brendan Creane <bcreane@gmail.com>
* ipn: reject advertised routes with non-address bits set
The config file path, EditPrefs local API, and App Connector API were
accepting invalid subnet route prefixes with non-address bits set (e.g.,
2a01:4f9:c010:c015::1/64 instead of 2a01:4f9:c010:c015::/64). All three
paths now reject prefixes where prefix != prefix.Masked() with an error
message indicating the expected masked form.
Updates tailscale/corp#36738
Signed-off-by: Brendan Creane <bcreane@gmail.com>
* address review comments
Signed-off-by: Brendan Creane <bcreane@gmail.com>
---------
Signed-off-by: Brendan Creane <bcreane@gmail.com>
The forwarder was not setting the Truncated (TC) flag when UDP DNS
responses exceeded either the EDNS buffer size (if present) or the
RFC 1035 default 512-byte limit. This affected DoH, TCP fallback,
and UDP response paths.
The fix ensures checkResponseSizeAndSetTC is called in all code paths
that return UDP responses, enforcing both EDNS and default UDP size
limits.
Added comprehensive unit tests and consolidated duplicate test helpers.
Updates #18107
Signed-off-by: Brendan Creane <bcreane@gmail.com>
Brendan CreaneandGitHub