From: Rich Felker <dalias@libc.org>
To: Florian Weimer <fw@deneb.enyo.de>
Cc: Andreas Schwab <schwab@linux-m68k.org>,
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
Subject: Re: XFS reports lchmod failure, but changes file system contents
Date: Wed, 12 Feb 2020 15:38:12 -0500 [thread overview]
Message-ID: <20200212203812.GE1663@brightrain.aerifal.cx> (raw)
In-Reply-To: <87sgjflfh8.fsf@mid.deneb.enyo.de>
On Wed, Feb 12, 2020 at 09:26:11PM +0100, Florian Weimer wrote:
> * Rich Felker:
>
> > On Wed, Feb 12, 2020 at 09:17:41PM +0100, Andreas Schwab wrote:
> >> 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.
> >
> > That text is outdated and should be corrected. Fixing fchmod fchown,
> > fstat, etc. to operate on O_PATH file descriptors was a very
> > intentional change in the kernel.
>
> I suppose we could do the S_ISLNK check, try fchmod, and if that
> fails, go via /proc. Is this the direction you want to go in?
It was, but Al Viro just pointed out to me that I was wrong. I think
we could use fstat (which AIUI now works) to do the S_ISLNK check, so
that it doesn't depend on /proc, but I don't see a way to do the chmod
operation without /proc at this time.
Rich
next prev parent reply other threads:[~2020-02-12 20:38 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
2020-02-12 20:19 ` Rich Felker
2020-02-12 20:26 ` Florian Weimer
2020-02-12 20:38 ` Rich Felker [this message]
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
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20200212203812.GE1663@brightrain.aerifal.cx \
--to=dalias@libc.org \
--cc=darrick.wong@oracle.com \
--cc=fw@deneb.enyo.de \
--cc=hch@infradead.org \
--cc=libc-alpha@sourceware.org \
--cc=linux-fsdevel@vger.kernel.org \
--cc=linux-xfs@vger.kernel.org \
--cc=schwab@linux-m68k.org \
--cc=viro@zeniv.linux.org.uk \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).