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Date: Wed, 12 Feb 2020 13:59:09 -0600
From: "A. Wilcox" <awilfox@...lielinux.org>
To: musl@...ts.openwall.com
Subject: Re: bug#39236: coreutils cp mishandles error return from
 lchmod

On 12/02/2020 13:07, Rich Felker wrote:
> On Wed, Feb 12, 2020 at 08:05:55AM -0500, Rich Felker wrote:
>> On Wed, Feb 12, 2020 at 12:50:19PM +0100, Florian Weimer wrote:
>>> * Paul Eggert:
>>>
>>>> On 1/22/20 2:05 PM, Rich Felker wrote:
>>>>> I think we're approaching a consensus that glibc should fix this too,
>>>>> so then it would just be gnulib matching the fix.
>>>>
>>>> I installed the attached patch to Gnulib in preparation for the upcoming 
>>>> glibc fix. The patch causes fchmodat with AT_SYMLINK_NOFOLLOW to work on 
>>>> non-symlinks, and similarly for lchmod on non-symlinks. The idea is to 
>>>> avoid this sort of problem in the future, and to let Coreutils etc. work 
>>>> on older platforms as if glibc 2.32 (or whatever) is already in place.
>>>
>>> The lchmod implementation based on /proc tickles an XFS bug:
>>>
>>>   <https://sourceware.org/ml/libc-alpha/2020-02/msg00467.html>
>>
>> Uhg, why does Linux even let the fs driver see whether the chmod is
>> being performed via a filename, O_PATH fd, or magic symlink in /proc?
>> It should just be an operation on the inode.
> 
> OK, I don't think it's actually clear from the test that the use of
> the magic symlink is the cause. It's plausible that XFS just always
> returns failure on success for this operation, and I don't have XFS to
> test with.


My root fs is XFS, but I only have musl to test with.  Is there a test
case I can run on musl to determine the behaviour of XFS for you?

The only glibc distribution that supports my platform is Void, so I
don't know if the Void glibc spin in a chroot would be sufficient if
there is no way to do this from a musl system.

Best,
--arw


-- 
A. Wilcox (awilfox)
Project Lead, Adélie Linux
https://www.adelielinux.org



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