From: Marc Zyngier <maz@kernel.org>
To: Al Viro <viro@zeniv.linux.org.uk>
Cc: syzbot <syzbot+e24baf53dc389927a7c3@syzkaller.appspotmail.com>,
davem@davemloft.net, kuba@kernel.org,
linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
netdev@vger.kernel.org, syzkaller-bugs@googlegroups.com
Subject: Re: general protection fault in sock_close
Date: Mon, 31 Aug 2020 21:39:27 +0100 [thread overview]
Message-ID: <82748fc422a64d70c706951954a2dcfa@kernel.org> (raw)
In-Reply-To: <20200831200328.GX1236603@ZenIV.linux.org.uk>
On 2020-08-31 21:03, Al Viro wrote:
> On Mon, Aug 31, 2020 at 12:48:13PM -0700, syzbot wrote:
>> Hello,
>>
>> syzbot found the following issue on:
>>
>> HEAD commit: 15bc20c6 Merge tag 'tty-5.9-rc3' of
>> git://git.kernel.org/p..
>> git tree: upstream
>> console output:
>> https://syzkaller.appspot.com/x/log.txt?x=16a85669900000
>> kernel config:
>> https://syzkaller.appspot.com/x/.config?x=891ca5711a9f1650
>> dashboard link:
>> https://syzkaller.appspot.com/bug?extid=e24baf53dc389927a7c3
>> compiler: clang version 10.0.0
>> (https://github.com/llvm/llvm-project/
>> c2443155a0fb245c8f17f2c1c72b6ea391e86e81)
>> syz repro:
>> https://syzkaller.appspot.com/x/repro.syz?x=127d3c99900000
>
>> The issue was bisected to:
>>
>> commit a9ed4a6560b8562b7e2e2bed9527e88001f7b682
>> Author: Marc Zyngier <maz@kernel.org>
>> Date: Wed Aug 19 16:12:17 2020 +0000
>>
>> epoll: Keep a reference on files added to the check list
>
> All of those are essentially duplicates.
>
> The minimal fix is below; I'm not happy with it long-term, but I'm
> still
> digging through the eventpoll locking, and there's a good chance that
> this
> is the least intrusive variant for -stable. Folks, could you check if
> the
> following patch fixes those suckers? Again, all reports bisected to
> that
> commit are essentially the same.
>
> diff --git a/fs/eventpoll.c b/fs/eventpoll.c
> index e0decff22ae2..8107e06d7f6f 100644
> --- a/fs/eventpoll.c
> +++ b/fs/eventpoll.c
> @@ -1995,9 +1995,9 @@ static int ep_loop_check_proc(void *priv, void
> *cookie, int call_nests)
> * during ep_insert().
> */
> if (list_empty(&epi->ffd.file->f_tfile_llink)) {
> - get_file(epi->ffd.file);
> - list_add(&epi->ffd.file->f_tfile_llink,
> - &tfile_check_list);
> + if (get_file_rcu(epi->ffd.file))
> + list_add(&epi->ffd.file->f_tfile_llink,
> + &tfile_check_list);
> }
> }
> }
I've managed to reproduce the issue using [1] (throw a few in a VM,
see things explode like clockwork).
With this patch on top of -rc3, the VM keep ticking away. FWIW:
Tested-by: Marc Zyngier <maz@kernel.org>
Fixes: a9ed4a6560b8 ("epoll: Keep a reference on files added to the
check list")
Thanks,
M.
[1] https://syzkaller.appspot.com/x/repro.c?x=140a19a9900000
--
Jazz is not dead. It just smells funny...
prev parent reply other threads:[~2020-08-31 20:39 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-08-31 19:48 general protection fault in sock_close syzbot
2020-08-31 20:03 ` Al Viro
2020-08-31 20:39 ` Marc Zyngier [this message]
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