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Bug#816155: marked as done (Assertion failure in gethostbyname )

Your message dated Thu, 2 Jan 2020 21:42:26 +0100
with message-id <20200102204226.GA217638@aurel32.net>
and subject line Re: Bug#868076: libc6: gethostbyname assertion failure on m68k
has caused the Debian Bug report #868076,
regarding Assertion failure in gethostbyname 
to be marked as done.

This means that you claim that the problem has been dealt with.
If this is not the case it is now your responsibility to reopen the
Bug report if necessary, and/or fix the problem forthwith.

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-- 
868076: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=868076
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--- Begin Message --- 
Package: libc6
Version: 2.21-9
User: debian-68k@lists.debian.org
Usertags: m68k

Hi,
Backstory: I maintain polyml, and was porting it to m68k; when running the test suite, I received an assertion failure in glibc in a call to gethostbyname.

It seems gethostbyname is broken, failing for me with “nss_files/files-hosts.c:218: _nss_files_gethostbyname3_r: Assertion `(bufferend - (char *) 0) % sizeof (char *) == 0' failed.” This can be reproduced with the following simple program:

    #include <stdio.h>
    #include <netdb.h>

    int main(int argc, char **argv) {
        struct hostent *h = gethostbyname("localhost");
        printf("name: %s\n", h->h_name);
        return 0;
    }

Delving inside glibc, _nss_files_gethostbyname3_r expects result->h_aliases to be aligned to sizeof(char *), as can be seen in the assert (bufferend points to an element in result->h_aliases, and each element is a char *). Provided this is true when the function is called, it seems to correctly maintain the invariant by rounding up bufferend when necessary.

However, the initial value of result->h_aliases is not aligned to sizeof(char *). Instead, it is assigned in parse_list (nss_files/files-parse.c:245) and aligned to __alignof__(char *). On many architectures, these are the same, but on m68k, __alignof__(char *) == 2, but sizeof(char *) == 4. There may be environments where result->h_aliases happens to be aligned to sizeof(char *) by chance, but that is most certainly not the case on mine (latest unstable running in ARAnyM).

I don’t know why bufferend is required to be aligned to sizeof(char *), and believe that imposing __alignof__(char *) in _nss_files_gethostbyname3_r instead would suffice. Alternatively, parse_list could choose MAX(sizeof(char *), __alignof__(char *)) as the alignment. Either way, the implementation as a whole is currently broken.

Regards,
James

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--- End Message ---
--- Begin Message --- 
Version: 2.27-1

On 2017-07-11 21:21, James Clarke wrote:
> Package: libc6
> Version: 2.24-12
> Tags: upstream patch
> Forwarded: https://sourceware.org/ml/libc-alpha/2017-07/msg00466.html
> User: debian-68k@lists.debian.org
> Usertags: m68k
> X-Debbugs-Cc: debian-68k@lists.debian.org
> 
> Hi,
> On m68k, gethostbyname can sometimes cause an assertion failure:
> 
> > "nss_files/files-hosts.c:218: _nss_files_gethostbyname3_r: Assertion `(bufferend - (char *) 0) % sizeof (char *) == 0' failed."
> 

According to upstream this problem has been fixed in version 2.27-1. I
am therefore closing the bug with that version.

-- 
Aurelien Jarno                          GPG: 4096R/1DDD8C9B
aurelien@aurel32.net                 http://www.aurel32.net

--- End Message ---
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