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Date: Sat, 27 Jan 2024 16:03:32 +0100
From: Michał Górny <mgorny@...too.org>
To: musl@...ts.openwall.com
Subject: [Bug?] getaddrinfo() fills .ai_canonname when AI_CANONNAME isn't
passed
Hello,
While debugging a test suite failure in dnspython [1], we've discovered
that the musl implementation of getaddrinfo() fills .ai_canonname field
even if flags do not include AI_CANONNAME. We think that this could
incorrect. Per POSIX:
> If nodename is not null, and if requested by the AI_CANONNAME flag,
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> the ai_canonname field of the first returned addrinfo structure shall
> point to a null-terminated string containing the canonical name
> corresponding to the input nodename; [...]
>
> All fields in socket address structures returned by getaddrinfo() that
> are not filled in through an explicit argument (for example,
> sin6_flowinfo) shall be set to zero. [2]
I think the correct behavior would be to set the field to zero (i.e.
null) when AI_CANONNAME is not present in flags.
I've reproduced the problem on Gentoo Linux amd64 with musl 1.2.4, using
the following test program:
```
#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netdb.h>
int main(void)
{
struct addrinfo hints = {0};
struct addrinfo *res;
struct addrinfo *p;
hints.ai_family = AF_UNSPEC;
hints.ai_socktype = SOCK_STREAM;
hints.ai_flags = 0;
if (getaddrinfo("example.com", NULL, &hints, &res) == 0) {
printf("%s\n", res->ai_canonname ? res->ai_canonname
: "(null)");
freeaddrinfo(res);
}
return 0;
}
```
On glibc system, it produces "(null)". On musl system, it produces
"example.com".
[1] https://github.com/rthalley/dnspython/issues/1035
[2] https://pubs.opengroup.org/onlinepubs/9699919799/functions/getaddrinfo.html
--
Best regards,
Michał Górny
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