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From: Florian Weimer <fw@deneb.enyo.de>
To: "Darrick J. Wong" <darrick.wong@oracle.com>
Cc: Christoph Hellwig <hch@infradead.org>,
	linux-xfs@vger.kernel.org, libc-alpha@sourceware.org,
	linux-fsdevel@vger.kernel.org, viro@zeniv.linux.org.uk,
	Rich Felker <dalias@libc.org>
Subject: Re: XFS reports lchmod failure, but changes file system contents
Date: Wed, 12 Feb 2020 20:15:08 +0100
Message-ID: <87d0ajmxc3.fsf@mid.deneb.enyo.de> (raw)
In-Reply-To: <20200212183718.GQ6870@magnolia> (Darrick J. Wong's message of "Wed, 12 Feb 2020 10:37:18 -0800")

* Darrick J. Wong:

> On Wed, Feb 12, 2020 at 10:11:28AM -0800, Christoph Hellwig wrote:
>> On Wed, Feb 12, 2020 at 08:16:04AM -0800, Darrick J. Wong wrote:
>> > xfs_setattr_nonsize calls posix_acl_chmod which returns EOPNOTSUPP
>> > because the xfs symlink inode_operations do not include a ->set_acl
>> > pointer.
>> > 
>> > I /think/ that posix_acl_chmod code exists to enforce that the file mode
>> > reflects any acl that might be set on the inode, but in this case the
>> > inode is a symbolic link.
>> > 
>> > I don't remember off the top of my head if ACLs are supposed to apply to
>> > symlinks, but what do you think about adding get_acl/set_acl pointers to
>> > xfs_symlink_inode_operations and xfs_inline_symlink_inode_operations ?
>> 
>> Symlinks don't have permissions or ACLs, so adding them makes no
>> sense.
>
> Ahh, I thought so!
>
>> xfs doesn't seem all that different from the other file systems,
>> so I suspect you'll also see it with other on-disk file systems.
>
> Yeah, I noticed that btrfs seems to exhibit the same behavior.
>
> I also noticed that ext4 actually /does/ implement [gs]et_acl for
> symlinks.

Rich Felker noticed this, which may be related:

| Further, I've found some inconsistent behavior with ext4: chmod on the
| magic symlink fails with EOPNOTSUPP as in Florian's test, but fchmod
| on the O_PATH fd succeeds and changes the symlink mode. This is with
| 5.4. Cany anyone else confirm this? Is it a problem?

It looks broken to me because fchmod (as an inode-changing operation)
is not supposed to work on O_PATH descriptors.

  reply index

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-02-12 11:48 Florian Weimer
2020-02-12 12:15 ` Florian Weimer
2020-02-12 16:16 ` Darrick J. Wong
2020-02-12 18:11   ` Christoph Hellwig
2020-02-12 18:37     ` Darrick J. Wong
2020-02-12 19:15       ` Florian Weimer [this message]
2020-02-12 19:51         ` Al Viro
2020-02-12 19:55           ` Rich Felker
2020-02-12 20:01           ` Florian Weimer
2020-02-12 20:17             ` Andreas Schwab
2020-02-12 20:19               ` Rich Felker
2020-02-12 20:26                 ` Florian Weimer
2020-02-12 20:38                   ` Rich Felker
2020-02-12 20:27                 ` Al Viro
2020-02-12 20:36                   ` Rich Felker
2020-02-12 20:18             ` Rich Felker
2020-02-12 20:38             ` Paul Eggert
2020-02-21  4:09             ` Aleksa Sarai
2020-02-21  5:02               ` Al Viro
2020-02-21  5:21                 ` Aleksa Sarai
2020-02-12 18:50     ` Florian Weimer
2020-02-12 18:55       ` Christoph Hellwig

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