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: Mon, 4 Mar 2019 02:36:18 +0000 [thread overview]
Message-ID: <20190304023618.GS2217@ZenIV.linux.org.uk> (raw)
In-Reply-To: <CAHk-=widuz9QBY-Xhpc1YHf=EV1uRGyOv-v-BNSa1zW-nCCC6Q@mail.gmail.com>
On Sun, Mar 03, 2019 at 02:23:33PM -0800, Linus Torvalds wrote:
OK, having dug through the archives, the reasons were not strong.
So that part is OK...
> @@ -1060,6 +1071,8 @@ static inline void iocb_put(struct aio_kiocb *iocb)
> {
> if (refcount_read(&iocb->ki_refcnt) == 0 ||
> refcount_dec_and_test(&iocb->ki_refcnt)) {
> + if (iocb->ki_filp)
> + fput(iocb->ki_filp);
> percpu_ref_put(&iocb->ki_ctx->reqs);
> kmem_cache_free(kiocb_cachep, iocb);
> }
That reminds me - refcount_t here is rather ridiculous; what we
have is
* everything other than aio_poll: ki_refcnt is 0 all along
* aio_poll: originally 0, then set to 2, then two iocb_put()
are done (either both synchronous to aio_poll(), or one sync and one
async).
That's not a refcount at all. It's a flag, set only for aio_poll ones.
And that test in iocb_put() is "if flag is set, clear it and bugger off".
What's worse, AFAICS the callers in aio_poll() are buggered (see below)
> static inline void aio_poll_complete(struct aio_kiocb *iocb, __poll_t mask)
> {
> - struct file *file = iocb->poll.file;
> -
> aio_complete(iocb, mangle_poll(mask), 0);
> - fput(file);
> }
No reasons to keep that function at all now...
> - if (unlikely(apt.error)) {
> - fput(req->file);
> + if (unlikely(apt.error))
> return apt.error;
> - }
>
> if (mask)
> aio_poll_complete(aiocb, mask);
Looking at that thing... How does it manage to avoid leaks
when we try to use it on e.g. /dev/tty, which has
poll_wait(file, &tty->read_wait, wait);
poll_wait(file, &tty->write_wait, wait);
in n_tty_poll()?
AFAICS, we'll succeed adding it to the first queue, then have
aio_poll_queue_proc() fail and set apt.error to -EINVAL.
Suppose we are looking for EPOLLIN and there's nothing ready
to read. We'll go
mask = vfs_poll(req->file, &apt.pt) & req->events;
mask is 0.
if (unlikely(!req->head)) {
nope - it's &tty->read_wait, not NULL
/* we did not manage to set up a waitqueue, done */
goto out;
}
spin_lock_irq(&ctx->ctx_lock);
spin_lock(&req->head->lock);
if (req->woken) {
nope - no wakeups so far
/* wake_up context handles the rest */
mask = 0;
apt.error = 0;
} else if (mask || apt.error) {
apt.error is non-zero
/* if we get an error or a mask we are done */
WARN_ON_ONCE(list_empty(&req->wait.entry));
list_del_init(&req->wait.entry);
OK, removed from queue
} else {
/* actually waiting for an event */
list_add_tail(&aiocb->ki_list, &ctx->active_reqs);
aiocb->ki_cancel = aio_poll_cancel;
}
spin_unlock(&req->head->lock);
spin_unlock_irq(&ctx->ctx_lock);
out:
if (unlikely(apt.error)) {
fput(req->file);
return apt.error;
... and we return -EINVAL to __io_submit_one(), where we hit
/*
* If ret is 0, we'd either done aio_complete() ourselves or have
* arranged for that to be done asynchronously. Anything non-zero
* means that we need to destroy req ourselves.
*/
if (ret)
goto out_put_req;
return 0;
out_put_req:
if (req->ki_eventfd)
eventfd_ctx_put(req->ki_eventfd);
iocb_put(req);
out_put_reqs_available:
put_reqs_available(ctx, 1);
return ret;
and all knowledge of req is lost. But we'd done only *one* iocb_put() in
that case, and ->ki_refcnt had been set to 2 by aio_poll(). How could it
avoid a leak? The same goes for "->poll() returns something without
bothering to call poll_wait()" case, actually...
IOW, I would rather have aio_poll() (along with your fput-a-bit-later change)
do this -
out:
if (mask && !apt.error)
aio_complete(aiocb, mangle_poll(mask), 0);
iocb_put(aiocb);
return apt.error;
Comments?
next prev parent reply other threads:[~2019-03-04 2:36 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
2019-03-03 22:23 ` Linus Torvalds
2019-03-04 2:36 ` Al Viro [this message]
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
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20190304023618.GS2217@ZenIV.linux.org.uk \
--to=viro@zeniv.linux.org.uk \
--cc=davem@davemloft.net \
--cc=eric.dumazet@gmail.com \
--cc=hch@lst.de \
--cc=jbaron@akamai.com \
--cc=kgraul@linux.ibm.com \
--cc=ktkhai@virtuozzo.com \
--cc=kyeongdon.kim@lge.com \
--cc=linux-kernel@vger.kernel.org \
--cc=netdev@vger.kernel.org \
--cc=pabeni@redhat.com \
--cc=syzkaller-bugs@googlegroups.com \
--cc=torvalds@linux-foundation.org \
--cc=xiyou.wangcong@gmail.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).