GNU bug report logs - #17010
Bug#739752: coreutils: ln segfaults when run with --relative and an empty target

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From: Pádraig Brady <P <at> draigBrady.com>
To: Jim Meyering <jim <at> meyering.net>
Cc: Erik Bernstein <erik <at> fscking.org>, 17010 <at> debbugs.gnu.org, Debian Bug Tracking System <submit <at> bugs.debian.org>, 739752 <739752 <at> bugs.debian.org>
Subject: bug#17010: Bug#739752: coreutils: ln segfaults when run with --relative and an empty target
Date: Fri, 14 Mar 2014 11:49:53 +0000

On 03/14/2014 03:44 AM, Jim Meyering wrote:
> On Thu, Mar 13, 2014 at 7:22 PM, Pádraig Brady <P <at> draigbrady.com> wrote:

>> Interesting. So canonicalize_filename_mode() can fail in this case,
>> even with CAN_MISSING. It's unexpected that c_f_m() sets errno=ENOENT
>> when CAN_MISSING is set. I wonder should we change that instead
>> in gnulib? With CAN_MISSING I would expect this function to work
>> on arbitrary strings, including the empty string.
> 
> What would you have c_f_m("", CAN_MISSING) return?
> I know of no absolute name corresponding to the dot-relative empty string.

Since with CAN_MISSING we should be just degenerating to string processing,
I would think it slightly better to return xstrdup(""),
to avoid special casing that in each caller.

I also notice that c_f_m() can return ENOMEM (from areadlink_with_size).
It's arguable that we should xalloc_die() within c_f_m()
for consistency in that case.

However I also notice that c_f_m("", CAN_MISSING) can return ENOENT
if the current working dir is unlinked.  I'm not sure
there is anything else we could do within c_f_m() to handle that.

Hence since c_f_m() can validly fail even with CAN_MISSING,
I agree your patch is correct.

Please push.

thanks!
Pádraig.

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