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From: Al Viro <viro@zeniv.linux.org.uk>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Eric Dumazet <eric.dumazet@gmail.com>,
	David Miller <davem@davemloft.net>,
	Jason Baron <jbaron@akamai.com>,
	kgraul@linux.ibm.com, ktkhai@virtuozzo.com,
	kyeongdon.kim@lge.com,
	Linux List Kernel Mailing <linux-kernel@vger.kernel.org>,
	Netdev <netdev@vger.kernel.org>,
	pabeni@redhat.com, syzkaller-bugs@googlegroups.com,
	xiyou.wangcong@gmail.com, Christoph Hellwig <hch@lst.de>
Subject: Re: [PATCH] aio: prevent the final fput() in the middle of vfs_poll() (Re: KASAN: use-after-free Read in unix_dgram_poll)
Date: Sun, 3 Mar 2019 20:30:11 +0000	[thread overview]
Message-ID: <20190303203011.GR2217@ZenIV.linux.org.uk> (raw)
In-Reply-To: <CAHk-=wiQ2YNB+2FT+jbdcC6qfYqvS2kLLAZbmPE_7sLfUPwFJg@mail.gmail.com>

On Sun, Mar 03, 2019 at 11:44:33AM -0800, Linus Torvalds wrote:
> On Sun, Mar 3, 2019 at 7:18 AM Al Viro <viro@zeniv.linux.org.uk> wrote:
> >
> > > Maybe unrelated to this bug, but...  What's to prevent a wakeup
> > > that happens just after we'd been added to a waitqueue by ->poll()
> > > triggering aio_poll_wake(), which gets to aio_poll_complete()
> > > with its fput() *before* we'd reached the end of ->poll() instance?
> 
> I'm assuming you're talking about the second vfs_poll() in
> aio_poll_complete_work()? The one we call before we check for
> "rew->cancelled" properly under the spinlock?

No.  The first one, right in aio_poll().

> But as far as I can tell, they *all* could do:
> 
>  - look up file in aio_submit() when allocating and creating the aio_kiocb
> 
>  - drop the filp in 'iocb_put()' (which happens whether things
> complete successfully or not).
>
> and we'd have avoided a lot of complexity, and we'd have avoided this bug.
> 
> Your patch fixes the poll() case, but it does so by just letting the
> existing complexity remain, and adding a second fget/fput pair in the
> poll logic.
> 
> It would seem like it would be much better to rip all the complexity
> out entirely, and replace it with sane, simple and obviously correct
> code.
> 
> Hmm?
> 
> In other words, why wouldn't something like the attached work instead?
 
I'll need to dig out the mail archive from last year, but IIRC this
had been considered and there'd been non-trivial problems.  Give me
an hour or so and I'll dig that out (there'd been many rounds of
review, with long threads involved, some private, some on fsdevel).

> @@ -1060,6 +1071,7 @@ static inline void iocb_put(struct aio_kiocb *iocb)
>  {
>  	if (refcount_read(&iocb->ki_refcnt) == 0 ||
>  	    refcount_dec_and_test(&iocb->ki_refcnt)) {
> +		fput(iocb->ki_filp);

Trivial oops here - it might be NULL.

  parent reply	other threads:[~2019-03-03 20:30 UTC|newest]

Thread overview: 53+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-03-03 10:22 KASAN: use-after-free Read in unix_dgram_poll syzbot
2019-03-03 13:55 ` Al Viro
2019-03-03 15:18   ` [PATCH] aio: prevent the final fput() in the middle of vfs_poll() (Re: KASAN: use-after-free Read in unix_dgram_poll) Al Viro
2019-03-03 18:37     ` Eric Dumazet
2019-03-03 19:44     ` Linus Torvalds
2019-03-03 20:13       ` Linus Torvalds
2019-03-03 20:30       ` Al Viro [this message]
2019-03-03 22:23         ` Linus Torvalds
2019-03-04  2:36           ` Al Viro
2019-03-04 21:22             ` Linus Torvalds
2019-03-07  0:03               ` [PATCH 1/8] aio: make sure file is pinned Al Viro
2019-03-07  0:03                 ` [PATCH 2/8] aio_poll_wake(): don't set ->woken if we ignore the wakeup Al Viro
2019-03-07  2:18                   ` Al Viro
2019-03-08 11:16                     ` zhengbin (A)
2019-03-07  0:03                 ` [PATCH 3/8] aio_poll(): sanitize the logics after vfs_poll(), get rid of leak on error Al Viro
2019-03-07  2:11                   ` zhengbin (A)
2019-03-07  0:03                 ` [PATCH 4/8] aio_poll(): get rid of weird refcounting Al Viro
2019-03-07  0:03                 ` [PATCH 5/8] make aio_read()/aio_write() return int Al Viro
2019-03-07  0:03                 ` [PATCH 6/8] move dropping ->ki_eventfd into iocb_put() Al Viro
2019-03-07  0:03                 ` [PATCH 7/8] deal with get_reqs_available() in aio_get_req() itself Al Viro
2019-03-07  0:03                 ` [PATCH 8/8] aio: move sanity checks and request allocation to io_submit_one() Al Viro
2019-03-07  0:23                 ` [PATCH 1/8] aio: make sure file is pinned Linus Torvalds
2019-03-07  0:41                   ` Al Viro
2019-03-07  0:48                     ` Al Viro
2019-03-07  1:20                       ` Al Viro
2019-03-07  1:30                         ` Linus Torvalds
2019-03-08  3:36                           ` Al Viro
2019-03-08 15:50                             ` Christoph Hellwig
2019-03-10  7:06                             ` Al Viro
2019-03-10  7:08                               ` [PATCH 1/8] pin iocb through aio Al Viro
2019-03-10  7:08                                 ` [PATCH 2/8] keep io_event in aio_kiocb Al Viro
2019-03-11 19:43                                   ` Christoph Hellwig
2019-03-11 21:17                                     ` Al Viro
2019-03-10  7:08                                 ` [PATCH 3/8] aio: store event at final iocb_put() Al Viro
2019-03-11 19:44                                   ` Christoph Hellwig
2019-03-11 21:13                                     ` Al Viro
2019-03-11 22:52                                       ` Al Viro
2019-03-10  7:08                                 ` [PATCH 4/8] Fix aio_poll() races Al Viro
2019-03-11 19:58                                   ` Christoph Hellwig
2019-03-11 21:06                                     ` Al Viro
2019-03-12 19:18                                       ` Christoph Hellwig
2019-03-10  7:08                                 ` [PATCH 5/8] make aio_read()/aio_write() return int Al Viro
2019-03-11 19:44                                   ` Christoph Hellwig
2019-03-10  7:08                                 ` [PATCH 6/8] move dropping ->ki_eventfd into iocb_destroy() Al Viro
2019-03-11 19:46                                   ` Christoph Hellwig
2019-03-10  7:08                                 ` [PATCH 7/8] deal with get_reqs_available() in aio_get_req() itself Al Viro
2019-03-11 19:46                                   ` Christoph Hellwig
2019-03-10  7:08                                 ` [PATCH 8/8] aio: move sanity checks and request allocation to io_submit_one() Al Viro
2019-03-11 19:48                                   ` Christoph Hellwig
2019-03-11 21:12                                     ` Al Viro
2019-03-11 19:41                                 ` [PATCH 1/8] pin iocb through aio Christoph Hellwig
2019-03-11 19:41                               ` [PATCH 1/8] aio: make sure file is pinned Christoph Hellwig
2019-03-04  7:53     ` [PATCH] aio: prevent the final fput() in the middle of vfs_poll() (Re: KASAN: use-after-free Read in unix_dgram_poll) Dmitry Vyukov

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