GNU bug report logs - #11761
Slight bug in split :-)

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Message #16 received at 11761-done <at> debbugs.gnu.org (full text, mbox):

From: Pádraig Brady <P <at> draigBrady.com>
To: Jim Meyering <jim <at> meyering.net>
Cc: François Pinard <pinard <at> iro.umontreal.ca>,
	11761-done <at> debbugs.gnu.org
Subject: Re: bug#11761: Slight bug in split :-)
Date: Fri, 22 Jun 2012 09:47:59 +0100

[Message part 1 (text/plain, inline)]

On 06/22/2012 08:56 AM, Jim Meyering wrote:
> Pádraig Brady wrote:
> ...
>> diff --git a/src/split.c b/src/split.c
>> index 53ee271..3e3313a 100644
>> --- a/src/split.c
>> +++ b/src/split.c
>> @@ -92,6 +92,9 @@ static char const *additional_suffix;
>>  /* Name of input file.  May be "-".  */
>>  static char *infile;
>>
>> +/* stat buf for input file.  */
>> +static struct stat in_stat_buf;
>> +
>>  /* Descriptor on which output file is open.  */
>>  static int output_desc = -1;
>>
>> @@ -362,6 +365,17 @@ create (const char *name)
>>      {
>>        if (verbose)
>>          fprintf (stdout, _("creating file %s\n"), quote (name));
>> +
>> +      struct stat out_stat_buf;
>> +      if (stat (name, &out_stat_buf) == 0)
>> +        {
>> +          if (SAME_INODE (in_stat_buf, out_stat_buf))
>> +            error (EXIT_FAILURE, 0, _("%s would overwrite input. Aborting."),
>> +                   quote (name));
>> +        }
>> +      else if (errno != ENOENT)
>> +        error (EXIT_FAILURE, errno, _("cannot stat %s"), quote (name));
>> +
>>        return open (name, O_WRONLY | O_CREAT | O_TRUNC | O_BINARY,
>>                     (S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP | S_IROTH | S_IWOTH))
>>      }
> 
> Hi Pádraig,
> 
> Thanks for taking this on.
> That introduces a minor TOCTOU race.
> It would probably never matter in practice,
> but who knows... if we can avoid it, why not?
> What do you think about something like this?
> 
>     int fd = open (name, (... as above, but without O_TRUNC...)...
>     if (fd < 0)
>       return fd;
>     if ( ! fstat (fd, &out_stat_buf))
>       error (EXIT_FAILURE, errno, _("failed to fstat %s"), quote (name));
>     if (SAME_INODE (in_stat_buf, out_stat_buf))
>       error (EXIT_FAILURE, 0, _("%s would overwrite input. Aborting."),
>              quote (name));
>     if ( ! ftruncate (fd, 0))
>       error ...
>     return fd;
> 
> The above might even be a tiny bit faster for long names,
> since it resolves each name only once.

Well probably slower due to the extra truncate syscall,
but point taken on the unlikely TOCTOU race.

I'll push the attached in a while.

cheers,
Pádraig.
> 

[split-input-guard.diff (text/plain, attachment)]

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