This PR enables DNS 0x20 as per
https://datatracker.ietf.org/doc/html/draft-vixie-dnsext-dns0x20-00 .
DNS 0x20 adds additional entropy to the request by randomly altering the
case of the DNS question to help prevent cache poisoning attacks.
Google DNS has implemented this support as of 2023, even though this is
a proposed and expired standard from 2008:
https://groups.google.com/g/public-dns-discuss/c/KxIDPOydA5M
There have been documented cases of name server and caching server
non-conformance, though it is expected to become more rare, especially
since Google has started using this.
This can be enabled via the `ARES_FLAG_DNS0x20` flag, which is currently
disabled by default. The test cases do however enable this flag to
validate this feature.
Implementors using this flag will notice that responses will retain the
mixed case, but since DNS names are case-insensitive, any proper
implementation should not be impacted.
There is currently no fallback mechanism implemented as it isn't
immediately clear how this may affect a stub resolver like c-ares where
we aren't querying the authoritative name server, but instead an
intermediate recursive resolver where some domains may return invalid
results while others return valid results, all while querying the same
nameserver. Likely using DNS cookies as suggested by #620 is a better
mechanism to fight cache poisoning attacks for stub resolvers.
TCP queries do not use this feature even if the `ARES_FLAG_DNS0x20` flag
is specified since they are not subject to cache poisoning attacks.
Fixes Issue: #795
Fix By: Brad House (@bradh352)
MSVC has been building with /W3 which isn't considered a safe level for
modern code. /W4 is recommended, but it too is lacking some recommended
options, so we enable /W4 and also the recommended options. We do,
however, have to disable a couple of options due to Windows headers not
being fully compliant sometimes as well as some things we do in c-ares
that it doesn't like, but aren't actually bad.
Fix By: Brad House (@bradh352)
When doing ares_gethostbyname() or ares_getaddrinfo() with AF_UNSPEC, if ares_cancel() was called after one address class was returned but before the other address class, it would return ARES_SUCCESS rather than ARES_ECANCELLED.
Test case has been added for this specific condition.
Fixes Bug: #662
Fix By: Brad House (@bradh352)
New DNS record parsing code. The old code was basically just some helper macros and functions for parsing an entire DNS message. The caller had to know the RFCs to use the parsers, except for some pre-made exceptions. The new parsing code parses the entire DNS message into an opaque data structure in a memory safe manner with various accessors for reading and manipulating the data.
The existing parser helpers for the various record types were reimplemented as wrappers around the new parser.
The accessors allow easy iteration across the DNS record datastructure, and can be used to easily create dig-like output without needing to know anything about the various record types and formats as dynamic helpers are provided for enumeration of values and data types of those values.
At some point in the future, this new DNS record structure, accessors, and parser will be exposed publicly. This is not done at this point as we don't want to do that until the API is completely stable. Likely a write() function to output the DNS record back into an actual message buffer will be introduced with the stable API as well.
Some subtle bugs in the existing code were uncovered, some which had test cases which turned out to be bogus. Validation with third-party implementations (e.g. BIND9) were performed to validate such cases were indeed bugs.
Adding additional RR parsers such as for TLSA (#470) or SVCB/HTTPS (#566) are trivial now since focus can be put on only parsing the data within the RR, not the entire message. That said, as the new parser is not yet public, it isn't clear the best way to expose any new RRs (probably best to wait for the new parser to be public rather than hacking in another legacy function).
Some additional RRs that are part of DNS RFC1035 or EDNS RFC6891 that didn't have previously implemented parsers are now also implemented (e.g. HINFO, OPT). Any unrecognized RRs are encapsulated into a "RAW_RR" as binary data which can be inserted or extracted, but are otherwise not interpreted in any way.
Fix By: Brad House (@bradh352)
All files have their licence and copyright information clearly
identifiable. If not in the file header, they are set separately in
.reuse/dep5.
All used license texts are provided in LICENSES/
There is too much inconsistency between platforms for arpa/nameser.h and arpa/nameser_compat.h for the way the current files are structured. Still load the respective system files but make our private nameser.h more forgiving.
Fixes: #388
Fix By: Brad House (@bradh352)
The rc4 function iterates over a buffer of size buffer_len who's maximum
value is INT_MAX with a counter of type short that is not guaranteed to
have maximum size INT_MAX.
In circumstances where short is narrower than int and where buffer_len
is larger than the maximum value of a short, it may be possible to loop
infinitely as counter will overflow and never be greater than or equal
to buffer_len.
The solution is to make the comparison be between types of equal width.
This commit defines counter as an int.
Fix By: Fionn Fitzmaurice (@fionn)
Brad House
Gregor Jasny
Daniel Stenberg
Tim Wojtulewicz
Martin Holeš
Fionn Fitzmaurice