Re: Bug in getaddrinfo

[Rich Felker <dalias@libc.org>]

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On Fri, Jun 22, 2018 at 12:04:31AM +0200, Marco Dickert wrote:
> Hi all.
> 
> I found a bug in the musl implementation of getaddrinfo(). It apparently returns
> a bad ai_canonname value. I used this [1] code to produce the following results
                                        ^^^
Please attach testcases rather than linking to transient pastebins.
I've saved and attached the linked code here.

> on an alpine linux (edge):
> 
> ----
> alpine:~# ./addrinfo-test mail.misterunknown.de
> Result 0 0xda051c83080
> Canonname mail.misterunknown.de
> alpine:~# ./addrinfo-test mail.misterunknown.de.
> Result 0 0x53f7dac4080
> Canonname mail.misterunknown.de.
> ----
> 
> The problem is the trailing dot in the Commonname in the second example, which
> should not be there. See also this [2] bug report I opened in the first place.

Per POSIX,

    if the canonical name is not available, then ai_canonname shall
    refer to the nodename argument or a string with the same contents.

It's not entirely clear what "available" means, but I think it's
generally interpreted as meaning "the requested name is a CNAME".

On the other hand we already define availability for another case,
search domains, where a duplicate of the requested nodename argument
is not returned, so I think it's reasonable to make a change here too,
especially if that's what other implementations do. I'll take a look
at it.

Thanks for the report.

Rich

[-- Attachment #2: addrinfo-test.c --]
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#include <sys/types.h>

#include <sys/socket.h>

#include <netdb.h>

#include <stdio.h>

#include <string.h>



int main(int argc, char** argv) {

     struct addrinfo hints, *ai;

     int result;

     memset(&hints, 0, sizeof(hints));

     hints.ai_flags = AI_CANONNAME;

     hints.ai_family = PF_UNSPEC;

     hints.ai_socktype = SOCK_STREAM;

     hints.ai_protocol = IPPROTO_TCP;

     result = getaddrinfo(argv[1], NULL, &hints, &ai);

     printf("Result %d %p\n", result, ai);

     if (result == 0 && ai != NULL) {

          printf("Canonname %s\n", ai->ai_canonname);

     }

}