From: Al Viro <viro@zeniv.linux.org.uk>
To: Dave Chinner <david@fromorbit.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
syzbot <syzbot+7a8ba368b47fdefca61e@syzkaller.appspotmail.com>,
Alexei Starovoitov <ast@kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>,
linux-fsdevel <linux-fsdevel@vger.kernel.org>,
Linux List Kernel Mailing <linux-kernel@vger.kernel.org>,
syzkaller-bugs <syzkaller-bugs@googlegroups.com>,
Jan Kara <jack@suse.cz>, Jaegeuk Kim <jaegeuk@kernel.org>,
Joel Becker <jlbec@evilplan.org>, Mark Fasheh <mark@fasheh.com>
Subject: Re: KASAN: use-after-free Read in path_lookupat
Date: Mon, 25 Mar 2019 23:02:11 +0000 [thread overview]
Message-ID: <20190325230211.GR2217@ZenIV.linux.org.uk> (raw)
In-Reply-To: <20190325224823.GF26298@dastard>
On Tue, Mar 26, 2019 at 09:48:23AM +1100, Dave Chinner wrote:
> And when it comes to VFS inode reclaim, XFS does not implement
> ->evict_inode because there is nothing at the VFS level to do.
> And ->destroy_inode ends up doing cleanup work (e.g. freeing on-disk
> inodes) which is non-trivial, blocking work, but then still requires
> the struct xfs_inode to be written back to disk before it can bei
> freed. So it just gets marked "reclaimable" and background reclaim
> then takes care of it from there so we avoid synchronous IO in inode
> reclaim...
>
> This works because don't track dirty inode metadata in the VFS
> writeback code (it's tracked with much more precision in the XFS log
> infrastructure) and we don't write back inodes from the VFS
> infrastructure, either. It's all done based on internal state
> outside the VFS.
>
> And, because of this, the VFS cannot assume that it can free
> the struct inode after calling ->destroy_inode or even use
> call_rcu() to run a filesystem destructor because the filesystem
> may need to do work that needs to block and that's not allowed in an
> RCU callback...
In Linus' patch that's what you get with non-NULL ->destroy_inode
+ NULL ->destroy_inode_rcu, so XFS won't be screwed by that.
Said that, yes, XFS adds another fun twist there (AFAICS, it's
the only in-tree filesystem that pulls that off).
I would really like some comments from f2fs and ocfs2 folks, as well
as Jan - he's had much more recent contact with writeback code than
I have... Could somebody explain what's going on in f2fs and ocfs2
->drop_inode()? It _should_ be just a predicate; looks like both
are playing very odd games to work around writeback problems and
I wonder if there's a cleaner solution for that. I can try and dig
through maillist(s) archives, but I would really appreciate it
if somebody could give a braindump on the issues dealt with in there...
next prev parent reply other threads:[~2019-03-25 23:02 UTC|newest]
Thread overview: 37+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-11-28 17:40 KASAN: use-after-free Read in path_lookupat syzbot
2019-03-25 0:44 ` syzbot
2019-03-25 1:25 ` Linus Torvalds
2019-03-25 1:23 ` Linus Torvalds
2019-03-25 4:57 ` Al Viro
2019-03-25 9:15 ` Daniel Borkmann
2019-03-25 11:11 ` Al Viro
2019-03-25 11:17 ` Al Viro
2019-03-25 11:21 ` Daniel Borkmann
2019-03-25 18:36 ` Linus Torvalds
2019-03-25 19:18 ` Linus Torvalds
2019-03-25 21:14 ` Al Viro
2019-03-25 21:45 ` Linus Torvalds
2019-03-25 22:04 ` Daniel Borkmann
2019-03-25 22:13 ` Linus Torvalds
2019-03-25 22:41 ` Daniel Borkmann
2019-03-25 22:49 ` Al Viro
2019-03-25 23:37 ` Al Viro
2019-03-25 23:44 ` Alexei Starovoitov
2019-03-26 0:21 ` Al Viro
2019-03-26 1:38 ` ceph: fix use-after-free on symlink traversal Al Viro
2019-03-26 1:39 ` jffs2: " Al Viro
2019-03-26 1:40 ` ubifs: " Al Viro
2019-03-26 1:43 ` debugfs: " Al Viro
2019-03-26 10:41 ` ceph: " Jeff Layton
2019-03-26 11:38 ` Ilya Dryomov
2019-03-26 1:45 ` KASAN: use-after-free Read in path_lookupat Al Viro
2019-04-10 18:11 ` Al Viro
2019-04-10 19:44 ` Linus Torvalds
2019-03-25 19:43 ` Al Viro
2019-03-25 22:48 ` Dave Chinner
2019-03-25 23:02 ` Al Viro [this message]
[not found] ` <CAGe7X7mb=gK7zhSwmT_6mmmkcbjhZAOb=wj31BdUcHkNUPsm2Q@mail.gmail.com>
2019-03-26 4:15 ` Al Viro
2019-03-27 16:58 ` Jan Kara
2019-03-27 18:59 ` Al Viro
2019-03-28 9:00 ` Jan Kara
2019-03-27 17:22 ` Jan Kara
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