The DNS server format is insufficient for future configurations, such as
supporting DNS over TLS (DoT) and DNS over HTTPS (DoH), as well as
additional functionality such as domain-specific servers. Already, in
the case where different UDP and TCP ports are used, it is impossible to
represent in the current format.
In order to try to use some standardized format, we are going to define
our own URI schemes that should be parse-able by any URI parser. The new
scheme will only be used when the configuration cannot otherwise be
expressed using the current `ipaddr%iface:port` format, which is the
format used as the nameserver configuration in `/etc/resolv.conf`.
However, the parser `ares_set_servers_csv()` shall accept the new URI
scheme format even when it is not necessary.
This PR implements a URI parser and writer and hooks the basic usage
into `ares_set_servers_csv()` and `ares_get_servers_csv()` as well as
provides updated documentation in the relevant manpages.
We will define these URI schemes:
* `dns://` - Normal DNS server (UDP + TCP). We need to be careful not to
conflict with query params defined in
https://datatracker.ietf.org/doc/html/rfc4501 since we'd technically be
extending this URI scheme. Port defaults to `53`.
* `dns+tls://` - DNS over TLS. Port defaults to `853`.
* `dns+https://` - DNS over HTTPS. Port defaults to `443`.
We initially will define these query parameters (additional arguments
may be required in the future to specify options such as TLS certificate
validation rules):
* `tcpport` - TCP port to use, only for `dns://` scheme. The `port`
specified as part of the `authority` component of the URI will be used
for both UDP and TCP by default, this option will override the TCP port.
* `ipaddr` - Only for `dns+tls://` and `dns+https://`. If the
`authority` component of the URI contains a hostname, this is used to
specify the ip address of the hostname. If not specified, will need to
use a non-secure server to perform a DNS lookup to retrieve this
information. It is always recommended to have both the ip address and
fully qualified domain name specified.
* `hostname` - Only for `dns+tls://` and `dns+https://`. If the
`authority` component of the URI contains an ip address, this is used to
specify the fully qualified domain name of the server. If not specified,
will need to use a non-secure server to perform a DNS reverse lookup to
retrieve this information. It is always recommended to have both the ip
address and fully qualified domain name specified.
* `domain` - If specified, this server is a domain-specific server. Any
queries for this domain will be routed to this server. Multiple servers
may be tagged with the same domain.
Examples:
```
dns://8.8.8.8
dns://[2001:4860:4860::8888]
dns://[fe80::b542:84df:1719:65e3%en0]
dns://192.168.1.1:55
dns://192.168.1.1?tcpport=1153
dns://10.0.1.1?domain=myvpn.com
dns+tls://8.8.8.8?hostname=dns.google
dns+tls://one.one.one.one?ipaddr=1.1.1.1
```
NOTE: While we are defining the scheme for things like domain-specific
servers, DNS over TLS and DNS over HTTPS, the underlying implementations
for those features do not yet exist and therefore will result in errors
if they are attempted to be used.
### Non-compliance in implementation
All these could be easily implemented/fixed if desired, however any such
changes would be of no use to the current c-ares usage of URIs:
* Does not currently support relative references
* Requires use of the authority section, blank is not allowed
* The query string is interpreted to be in
[application/x-www-form-urlencoded](https://en.wikipedia.org/wiki/Application/x-www-form-urlencoded)
format only and will result in parse errors if it is not. This is the
most common format used, however technically not valid to mandate this
format is used. We could add flags in the future to treat the query
string as opaque and leave it to the user to process. Or we could
internally have a list of schemes that use this format.
* [IDNA](https://en.wikipedia.org/wiki/Internationalized_domain_name) is
not supported.
* Does not support hex-encoded IPv4 addresses (this is compliant with RFC3986, but not WHATWG)
Authored-By: Brad House (@bradh352)
At some point in time, internal non-public functions were prefixed with
`ares__` where as functions that may become public were prefixed with
just `ares_`. This was never very consistent. Organizing the code better
typically provides more benefit in this way, which we've made great
progress on.
All non-static symbols must contain the `ares_` prefix, and that should
be more than sufficient in preventing any sort of issues.
Authored-By: Brad House (@bradh352)
We modified the include path with recent changes, that isn't good for
OSS-Fuzz. Lets make the path relative for including some semi-public
headers to allow OSS-Fuzz to build again.
Fix By: Brad House (@bradh352)
The test case changes introduced a memory leak in the test itself
(not in c-ares). Fix this memory leak. Also move prior fuzzing
information into the new fuzzing document.
Fix By: Brad House (@bradh352)
The coverage of the fuzzer is fairly low as it was only testing the
parsing, not trying to read the data from the datastructure or writing
it back out as a DNS message. Lets extend, and also provide a
FUZZING.md to help people new to fuzzing get up and running.
Authored-By: Brad House (@bradh352)
The legacy c-ares parsers such as ares_parse_txt_reply() and
ares_parse_srv_reply() historically all used different logic and
parsing.
As of c-ares 1.21.0 these are simply wrappers around a single parser, and
simply convert the parsed DNS response into the data structures the legacy
parsers used which is a small amount of code and not likely going to vary
based on the input data.
Instead, these days, it makes more sense to test the new parser directly
instead of calling it 10 or 11 times with the same input data to speed up
the number of iterations per second the fuzzer can perform.
We are keeping this legacy fuzzer test for historic reasons or if someone
finds them of use hidden behind a define of USE_LEGACY_PARSERS.
Authored-By: Brad House (@bradh352)
c-ares uses multiple code styles, standardize on one. Talking with @bagder he feels strongly about maintaining an 80 column limit, but feels less strongly about things I feel strongly about (like alignment).
Can re-run the formatter on the codebase via:
```
clang-format -i */*.c */*.h */*/*.c */*/*.h
```
Fix By: Brad House (@bradh352)
PR #568 increased the warning levels and c-ares code emitted a bunch of warnings. This PR fixes those warnings and starts transitioning internal data types into more proper forms (e.g. data lengths should be size_t not int). It does, however, have to manually cast back to what the public API needs due to API and ABI compliance (we aren't looking to break integrations, just clean up internals).
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/
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
Daniel Stenberg
Martin Holeš
David Hotham
Fionn Fitzmaurice