From: Al Viro <viro@zeniv.linux.org.uk>
To: Ian Kent <raven@themaw.net>
Cc: Brian Foster <bfoster@redhat.com>,
"Darrick J. Wong" <djwong@kernel.org>,
Christoph Hellwig <hch@lst.de>,
Miklos Szeredi <miklos@szeredi.hu>,
David Howells <dhowells@redhat.com>,
Kernel Mailing List <linux-kernel@vger.kernel.org>,
linux-fsdevel <linux-fsdevel@vger.kernel.org>,
xfs <linux-xfs@vger.kernel.org>
Subject: Re: [PATCH] vfs: check dentry is still valid in get_link()
Date: Sat, 15 Jan 2022 06:38:39 +0000 [thread overview]
Message-ID: <YeJr7/E+9stwEb3t@zeniv-ca.linux.org.uk> (raw)
In-Reply-To: <164180589176.86426.501271559065590169.stgit@mickey.themaw.net>
On Mon, Jan 10, 2022 at 05:11:31PM +0800, Ian Kent wrote:
> When following a trailing symlink in rcu-walk mode it's possible for
> the dentry to become invalid between the last dentry seq lock check
> and getting the link (eg. an unlink) leading to a backtrace similar
> to this:
>
> crash> bt
> PID: 10964 TASK: ffff951c8aa92f80 CPU: 3 COMMAND: "TaniumCX"
> …
> #7 [ffffae44d0a6fbe0] page_fault at ffffffff8d6010fe
> [exception RIP: unknown or invalid address]
> RIP: 0000000000000000 RSP: ffffae44d0a6fc90 RFLAGS: 00010246
> RAX: ffffffff8da3cc80 RBX: ffffae44d0a6fd30 RCX: 0000000000000000
> RDX: ffffae44d0a6fd98 RSI: ffff951aa9af3008 RDI: 0000000000000000
> RBP: 0000000000000000 R8: ffffae44d0a6fb94 R9: 0000000000000000
> R10: ffff951c95d8c318 R11: 0000000000080000 R12: ffffae44d0a6fd98
> R13: ffff951aa9af3008 R14: ffff951c8c9eb840 R15: 0000000000000000
> ORIG_RAX: ffffffffffffffff CS: 0010 SS: 0018
> #8 [ffffae44d0a6fc90] trailing_symlink at ffffffff8cf24e61
> #9 [ffffae44d0a6fcc8] path_lookupat at ffffffff8cf261d1
> #10 [ffffae44d0a6fd28] filename_lookup at ffffffff8cf2a700
> #11 [ffffae44d0a6fe40] vfs_statx at ffffffff8cf1dbc4
> #12 [ffffae44d0a6fe98] __do_sys_newstat at ffffffff8cf1e1f9
> #13 [ffffae44d0a6ff38] do_syscall_64 at ffffffff8cc0420b
>
> Most of the time this is not a problem because the inode is unchanged
> while the rcu read lock is held.
>
> But xfs can re-use inodes which can result in the inode ->get_link()
> method becoming invalid (or NULL).
Without an RCU delay? Then we have much worse problems...
Details, please.
next prev parent reply other threads:[~2022-01-15 6:38 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-01-10 9:11 [PATCH] vfs: check dentry is still valid in get_link() Ian Kent
2022-01-15 6:38 ` Al Viro [this message]
2022-01-17 2:55 ` Ian Kent
2022-01-17 14:35 ` Brian Foster
2022-01-17 16:28 ` Al Viro
2022-01-17 18:10 ` Al Viro
2022-01-17 19:48 ` Al Viro
2022-01-18 1:32 ` Al Viro
2022-01-18 2:31 ` Ian Kent
2022-01-18 3:03 ` Al Viro
2022-01-18 13:47 ` Brian Foster
2022-01-18 18:25 ` Brian Foster
2022-01-18 19:20 ` Al Viro
2022-01-18 20:58 ` Brian Foster
2022-01-18 8:29 ` Christian Brauner
2022-01-18 16:04 ` Al Viro
2022-01-19 9:05 ` Christian Brauner
2022-01-17 18:42 ` Brian Foster
2022-01-18 3:00 ` Dave Chinner
2022-01-18 3:17 ` Al Viro
2022-01-18 4:12 ` Dave Chinner
2022-01-18 5:58 ` Al Viro
2022-01-18 23:25 ` Dave Chinner
2022-01-19 14:08 ` Brian Foster
2022-01-19 22:07 ` Dave Chinner
2022-01-20 16:03 ` Brian Foster
2022-01-20 16:34 ` Brian Foster
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