From: Greg KH <gregkh@linuxfoundation.org>
To: Rich Felker <dalias@libc.org>
Cc: linux-api@vger.kernel.org,
Alexander Viro <viro@zeniv.linux.org.uk>,
Christoph Hellwig <hch@infradead.org>,
linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 2/2] vfs: add fchmodat2 syscall
Date: Wed, 16 Sep 2020 08:19:43 +0200 [thread overview]
Message-ID: <20200916061943.GC142621@kroah.com> (raw)
In-Reply-To: <20200916002335.GQ3265@brightrain.aerifal.cx>
On Tue, Sep 15, 2020 at 08:23:38PM -0400, Rich Felker wrote:
> POSIX defines fchmodat as having a 4th argument, flags, that can be
> AT_SYMLINK_NOFOLLOW. Support for changing the access mode of symbolic
> links is optional (EOPNOTSUPP allowed if not supported), but this flag
> is important even on systems where symlinks do not have access modes,
> since it's the only way to safely change the mode of a file which
> might be asynchronously replaced with a symbolic link, without a race
> condition whereby the link target is changed.
>
> It's possible to emulate AT_SYMLINK_NOFOLLOW in userspace, and both
> musl libc and glibc do this, by opening an O_PATH file descriptor and
> performing chmod on the corresponding magic symlink in /proc/self/fd.
> However, this requires procfs to be mounted and accessible.
>
> Signed-off-by: Rich Felker <dalias@libc.org>
No kselftest for this new system call, or man page? How do we know this
actually works and what the expected outcome should be?
thanks,
greg k-h
prev parent reply other threads:[~2020-09-16 6:19 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-16 0:22 [PATCH v2 0/2] changes for addding fchmodat2 syscall Rich Felker
2020-09-16 0:22 ` [PATCH v2 1/2] vfs: block chmod of symlinks Rich Felker
2020-09-16 6:18 ` Greg KH
2020-09-16 6:23 ` Christoph Hellwig
2020-09-16 15:36 ` Rich Felker
2020-09-16 6:25 ` Christoph Hellwig
2020-09-16 15:41 ` Rich Felker
2020-09-17 4:07 ` Al Viro
2020-09-17 4:15 ` Al Viro
2020-09-17 18:42 ` Rich Felker
2020-09-29 17:49 ` Christoph Hellwig
2020-09-16 0:23 ` [PATCH v2 2/2] vfs: add fchmodat2 syscall Rich Felker
2020-09-16 6:01 ` Aleksa Sarai
2020-09-16 6:19 ` Greg KH [this message]
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