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From: Andreas Schwab <schwab@linux-m68k.org>
To: Florian Weimer <fw@deneb.enyo.de>
Cc: Al Viro <viro@zeniv.linux.org.uk>,
	"Darrick J. Wong" <darrick.wong@oracle.com>,
	Christoph Hellwig <hch@infradead.org>,
	linux-xfs@vger.kernel.org, libc-alpha@sourceware.org,
	linux-fsdevel@vger.kernel.org, Rich Felker <dalias@libc.org>
Subject: Re: XFS reports lchmod failure, but changes file system contents
Date: Wed, 12 Feb 2020 21:17:41 +0100	[thread overview]
Message-ID: <87wo8r1rx6.fsf@igel.home> (raw)
In-Reply-To: <87wo8rlgml.fsf@mid.deneb.enyo.de> (Florian Weimer's message of "Wed, 12 Feb 2020 21:01:22 +0100")

On Feb 12 2020, Florian Weimer wrote:

> * Al Viro:
>
>> On Wed, Feb 12, 2020 at 08:15:08PM +0100, Florian Weimer wrote:
>>
>>> | 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.
>>
>> Why?  O_PATH does have an associated inode just fine; where does
>> that "not supposed to" come from?
>
> It fails on most file systems right now.  I thought that was expected.
> Other system calls (fsetxattr IIRC) do not work on O_PATH descriptors,
> either.  I assumed that an O_PATH descriptor was not intending to
> confer that capability.  Even openat fails.

According to open(2), this is expected:

       O_PATH (since Linux 2.6.39)
              Obtain a file descriptor that can be used for two  purposes:  to
              indicate a location in the filesystem tree and to perform opera-
              tions that act purely at the file descriptor  level.   The  file
              itself  is not opened, and other file operations (e.g., read(2),
              write(2), fchmod(2), fchown(2), fgetxattr(2), ioctl(2), mmap(2))
              fail with the error EBADF.

Andreas.

-- 
Andreas Schwab, schwab@linux-m68k.org
GPG Key fingerprint = 7578 EB47 D4E5 4D69 2510  2552 DF73 E780 A9DA AEC1
"And now for something completely different."

  reply	other threads:[~2020-02-12 20:17 UTC|newest]

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-02-12 11:48 XFS reports lchmod failure, but changes file system contents 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
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 [this message]
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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