c-ares / c-ares / 11757190407

92%

main: 92%

Build Type

push

github

Committed by bradh352

Commit Message

Some upstream DNS servers are non-compliant with EDNS options

Some DNS servers don't properly ignore unknown EDNS options as the spec says they must, and instead will return EFORMERR.

See discussion roughly starting here: https://github.com/alpinelinux/docker-alpine/issues/366#issuecomment-2462530681

In this case the DNS server is known to support EDNS in general (as version prior to c-ares 1.33 worked which used EDNS), but when adding the EDNS DNS Cookie extension, they return EFORMERR.  This is in violation of [RFC6891 6.1.2](https://datatracker.ietf.org/doc/html/rfc6891#section-6.1.2):
> Any OPTION-CODE values not understood by a responder or requestor MUST be ignored.

The server in this example actual echo's back the EDNS record further causing confusion that makes you think they might understand the record.

We need to catch an EFORMERR and re-attempt the query without EDNS completely since they are really non-compliant with EDNS.  We may support additional EDNS extensions in the future and don't want to have to probe each individual extension with a braindead server.

Fixes #911
Authored-By: Brad House (@bradh352)

Run Details

32 of 34 new or added lines in 2 files covered. (94.12%)

8 existing lines in 2 files now uncovered.

22089 of 24211 relevant lines covered (91.24%)

11960.77 hits per line