bug-gnulib
[Top][All Lists]
Advanced

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: ‘unlinkat’ bug in Linux 4.0.2 leads to tar test failure


From: Ludovic Courtès
Subject: Re: ‘unlinkat’ bug in Linux 4.0.2 leads to tar test failure
Date: Sun, 24 May 2015 15:53:07 +0200
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/24.5 (gnu/linux)

Pádraig Brady <address@hidden> skribis:

> On 24/05/15 12:33, Ludovic Courtès wrote:

[...]

>> unlinkat(4, "foo_file", 0)              = 0
>> unlinkat(AT_FDCWD, "foo", AT_REMOVEDIR) = 0
>> unlinkat(5, "bar_file", 0)              = 0
>> unlinkat(4, "../bar", AT_REMOVEDIR)     = -1 ENOENT (No such file or 
>> directory)
>> --8<---------------cut here---------------end--------------->8---
>> 
>> Contrast this with the same thing on 4.0.4-gnu:
>> 
>> --8<---------------cut here---------------start------------->8---
>> unlinkat(4, "foo_file", 0)              = 0
>> unlinkat(AT_FDCWD, "foo", AT_REMOVEDIR) = 0
>> unlinkat(5, "bar_file", 0)              = 0
>> unlinkat(4, "../bar", AT_REMOVEDIR)     = 0
>> --8<---------------cut here---------------end--------------->8---
>> 
>> So this looks like a 4.0.2 kernel bug that Gnulib’s unlinkat should
>> perhaps work around.
>> 
>> Thoughts?
>
> Maybe. How widely deployed was 4.0.2 (It's not used in Red Hat land for 
> example).
> How many versions was the bug present for?

I don’t know, and I haven’t been able to find traces of a fix in that
area in the kernel.

OTOH, after rereading the analysis at
<http://lists.gnu.org/archive/html/bug-tar/2014-08/msg00010.html>, it
may be that the 4.0.2 behavior is POSIX-conforming, in which case we’d
rather fix tar (or its tests) instead:

  The BSD behavior appears to be in line with POSIX.  unlinkat() with
  AT_REMOVEDIR is equivalent to rmdir(), whose specification says:

    If one or more processes have the directory open when the last
    link is removed, the dot and dot-dot entries, if present, shall
    be removed before rmdir() returns and no new entries may be created
    in the directory, but the directory shall not be removed until
    all references to the directory are closed.

  Without "..", the path resolution of the subsequent unlinkat() call
  should--or at least can--fail.

WDYT?

Thanks,
Ludo’.



reply via email to

[Prev in Thread] Current Thread [Next in Thread]