GNU bug report logs - #63931
ls colors one symlink too much as non-broken in symlink chain

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From: help-debbugs <at> gnu.org (GNU bug Tracking System)
To: Martin Schulte <gnu <at> schrader-schulte.de>
Subject: bug#63931: closed (Re: bug#63931: ls colors one symlink too much
 as non-broken in symlink chain)
Date: Wed, 07 Jun 2023 15:02:02 +0000

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Your bug report

#63931: ls colors one symlink too much as non-broken in symlink chain

which was filed against the coreutils package, has been closed.

The explanation is attached below, along with your original report.
If you require more details, please reply to 63931 <at> debbugs.gnu.org.

-- 
63931: https://debbugs.gnu.org/cgi/bugreport.cgi?bug=63931
GNU Bug Tracking System
Contact help-debbugs <at> gnu.org with problems

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From: Pádraig Brady <P <at> draigBrady.com>
To: Martin Schulte <gnu <at> schrader-schulte.de>
Cc: 63931-done <at> debbugs.gnu.org
Subject: Re: bug#63931: ls colors one symlink too much as non-broken in
 symlink chain
Date: Wed, 7 Jun 2023 16:01:42 +0100

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On 07/06/2023 13:23, Pádraig Brady wrote:
> On 07/06/2023 10:56, Martin Schulte wrote:
>> Hello Paul, hello Pádraig,
>>
>> thanks a lot for your analysis and explanations!
>>
>>> With that in mind, the code change you proposed is reasonably innocuous,
>>> although it slows things down a bit in the usual case. Not sure it's
>>> worth doing (I guess it does fix a race but there are other unfixable
>>> races in this area....).
>>
>> I first supposed that the effect was caused by an off-by-one problem, but after understanding it, I think you are right here to ask if changing the behaviour is worth doing.
> 
> Well changing it makes things more consistent,
> and also simplifies ls.c as we can remove the make_link_name() function.
> 
>> Looking at
>>
>> $ ls {38..42}
>> ls: cannot access '41': Too many levels of symbolic links
>> ls: cannot access '42': Too many levels of symbolic links
>> 38  39  40
>>
>> shows that there would be more issues to consider in this case.
> 
> Indeed. That can be addressed with the following.
> 
> cheers,
> Pádraig
> 
> diff --git a/src/ls.c b/src/ls.c
> index fbeb9b6dc..33f692bb4 100644
> --- a/src/ls.c
> +++ b/src/ls.c
> @@ -3480,7 +3480,7 @@ gobble_file (char const *name, enum filetype type, ino_t inode,
>                    break;
> 
>                  need_lstat = (err < 0
> -                            ? errno == ENOENT
> +                            ? (errno == ENOENT || errno == ELOOP)
>                                : ! S_ISDIR (f->stat.st_mode));
>                  if (!need_lstat)
>                    break;

The complete two patches in this area are attached,
which I'll apply a bit later.

Marking this as done,

thanks,
Pádraig

[0001-ls-use-more-standard-symlink-traversal.patch (text/x-patch, attachment)]

[0002-ls-display-command-line-symlinks-that-return-ELOOP.patch (text/x-patch, attachment)]

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From: Martin Schulte <gnu <at> schrader-schulte.de>
To: bug-coreutils <at> gnu.org
Subject: ls colors one symlink too much as non-broken in symlink chain
Date: Tue, 6 Jun 2023 19:24:26 +0200

Hello coreutils-maintainers,

I create a long chain of symlinks - ls colors the 41st element as ok while the kernel already gives up after 40 symlinks:

$ uname -a
Linux martnix4 5.10.0-23-amd64 #1 SMP Debian 5.10.179-1 (2023-05-12) x86_64 GNU/Linux
$ ls --version | head -n 1
ls (GNU coreutils) 8.32
$ mkdir empty
$ cd empty
$ last=00 ; touch $last ; for ln in {01..50}; do ln -s $last $ln; last=$ln; done
$ ls --color -l {38..42}
lrwxrwxrwx 1 u g 2 Jun  6 19:00 38 -> 37   <- 38 colored as symlink
lrwxrwxrwx 1 u g 2 Jun  6 19:00 39 -> 38   <- 39 colored as symlink
lrwxrwxrwx 1 u g 2 Jun  6 19:00 40 -> 39   <- 40 colored as symlink
lrwxrwxrwx 1 u g 2 Jun  6 19:00 41 -> 40   <- 41 colored as symlink
lrwxrwxrwx 1 u g 2 Jun  6 19:00 42 -> 41   <- 42 and 41 colored as broken link
$ cat 40
$ cat 41
cat: 41: Too many levels of symbolic links

This could be reproduced with "ls (GNU coreutils) 9.3.45-6a618" compiled from the git repository.

Best regards,

Martin

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