From: Al Viro <viro@zeniv.linux.org.uk>
To: Miklos Szeredi <mszeredi@redhat.com>
Cc: Xavier Roche <xavier.roche@algolia.com>, linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH v2] vfs: fix link vs. rename race
Date: Tue, 13 Sep 2022 05:29:02 +0100 [thread overview]
Message-ID: <YyAHDsGiaA/0ksX8@ZenIV> (raw)
In-Reply-To: <Yx/lIWoLCWHwM6DO@ZenIV>
On Tue, Sep 13, 2022 at 03:04:17AM +0100, Al Viro wrote:
> On Mon, Feb 21, 2022 at 09:20:02AM +0100, Miklos Szeredi wrote:
>
> [digging through the old piles of mail]
>
> Eyes-watering control flow in do_linkat() aside (it's bound to rot; too
> much of it won't get any regression testing and it's convoluted enough
> to break easily), the main problem I have with that is the DoS potential.
>
> You have a system-wide lock, and if it's stuck you'll get every damn
> rename(2) stuck as well. Sure, having it taken only upon the race
> with rename() (or unlink(), for that matter) make it harder to get
> stuck with lock held, but that'll make the problem harder to reproduce
> and debug...
FWIW, how much trouble would we have if link(2) would do the following?
find the parent of source
lock it
look the child up
verify it's a non-directory
bump child's i_nlink
all failure exits past that point decrement child's i_nlink
unlock the parent
find the parent of destination
lock it
look the destination up
call vfs_link
decrement child's i_nlink - vfs_link has bumped it
unlock the parent of destination
I do realize it can lead to leaked link count on a crash, obviously...
next prev parent reply other threads:[~2022-09-13 4:35 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-02-21 8:20 [PATCH v2] vfs: fix link vs. rename race Miklos Szeredi
2022-02-21 8:56 ` Xavier Roche
2022-09-13 2:04 ` Al Viro
2022-09-13 4:29 ` Al Viro [this message]
2022-09-13 8:02 ` Amir Goldstein
2022-09-13 10:03 ` Miklos Szeredi
2022-09-13 4:41 ` NeilBrown
2022-09-13 5:20 ` Al Viro
2022-09-13 5:40 ` Al Viro
2022-09-14 0:14 ` NeilBrown
2022-09-14 1:30 ` Al Viro
2022-09-13 23:52 ` NeilBrown
2022-09-14 0:13 ` Al Viro
2022-09-16 6:13 ` [PATCH RFC] VFS: lock source directory for link to avoid " NeilBrown
2022-09-16 6:28 ` Miklos Szeredi
2022-09-16 6:45 ` NeilBrown
2022-09-16 6:49 ` Al Viro
2022-09-16 14:32 ` Amir Goldstein
2022-09-19 8:28 ` Christian Brauner
2022-09-19 22:56 ` NeilBrown
2022-09-23 3:02 ` [LTP] [VFS] 3fb4ec6faa: ltp.linkat02.fail kernel test robot
2022-09-23 3:02 ` kernel test robot
2022-09-23 3:02 ` kernel test robot
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