Re: WARNING in request_end

Dmitry Vyukov
2018-09-25T09:38:25Z

On Tue, Sep 25, 2018 at 11:18 AM, Kirill Tkhai <ktkhai@virtuozzo.com> wrote:
> On 24.09.2018 17:44, Miklos Szeredi wrote:
>> On Mon, Sep 24, 2018 at 2:29 PM, syzbot
>> <syzbot+ef054c4d3f64cd7f7cec@syzkaller.appspotmail.com> wrote:
>>> Hello,
>>>
>>> syzbot found the following crash on:
>>>
>>> HEAD commit: 6bf4ca7fbc85 Linux 4.19-rc5
>>> git tree: upstream
>>> console output: https://syzkaller.appspot.com/x/log.txt?x=159149c6400000
>>> kernel config: https://syzkaller.appspot.com/x/.config?x=22a62640793a83c9
>>> dashboard link: https://syzkaller.appspot.com/bug?extid=ef054c4d3f64cd7f7cec
>>> compiler: gcc (GCC) 8.0.1 20180413 (experimental)
>>>
>>> Unfortunately, I don't have any reproducer for this crash yet.
>>>
>>> IMPORTANT: if you fix the bug, please add the following tag to the commit:
>>> Reported-by: syzbot+ef054c4d3f64cd7f7cec@syzkaller.appspotmail.com
>>>
>>> WARNING: CPU: 0 PID: 9445 at fs/fuse/dev.c:390 request_end+0x82e/0xaa0
>>
>> And there we have the bug likely caused by the set_bit(FR_SENT, ...)
>> not being inside the fpq->lock-ed region.
>>
>> So that needs to be fixed anyway, apparently.
>
> I can't confirm, since I haven't found yet the direct way, that set_bit() results
> in this stack...
>
> We have one more (unrelated) possible use-after-free here:
>
> cpu0 cpu1
> fuse_dev_do_write() fuse_dev_do_write()
> req = request_find(fpq, oh.unique) ...
> spin_unlock(&fpq->lock) ...
> ... req = request_find(fpq, oh.unique)
> ... spin_unlock(&fpq->lock)
> queue_interrupt(&fc->iq, req); ...
> ... ...
> ... ...
> request freed ...
> ... queue_interrupt(&fc->iq, req); <- use after free
>
> Something like below is needed:

There is a bunch of open bugs in fuse on syzbot dashboard, perhaps
it's one of them:

https://syzkaller.appspot.com/bug?id=19aabec97cbf73dd0475d6e599113a7861c4b306
https://syzkaller.appspot.com/bug?id=24aa489e6929205e40ec4aa52cd8f47897f2ad63
https://syzkaller.appspot.com/bug?id=400d6a977a0dbd8836d7c7ec8481782a674ee855
https://syzkaller.appspot.com/bug?id=ff9ab4a23afa7553fb79f745a92be87ba4144508
https://syzkaller.appspot.com/bug?id=d0f258de27b6d7ccecbba09385b3376cc4a12ffe
https://syzkaller.appspot.com/bug?id=e8077bce636d52d9c40e1ea904699c27b7454354

> @@ -1875,16 +1877,20 @@ static ssize_t fuse_dev_do_write(struct fuse_dev *fud,
>
> /* Is it an interrupt reply? */
> if (req->intr_unique == oh.unique) {
> + __fuse_get_request(req);
> spin_unlock(&fpq->lock);
>
> err = -EINVAL;
> - if (nbytes != sizeof(struct fuse_out_header))
> + if (nbytes != sizeof(struct fuse_out_header)) {
> + fuse_put_request(fc, req);
> goto err_finish;
> + }
>
> if (oh.error == -ENOSYS)
> fc->no_interrupt = 1;
> else if (oh.error == -EAGAIN)
> queue_interrupt(&fc->iq, req);
> + fuse_put_request(fc, req);
>
> fuse_copy_finish(cs);
> return nbytes;
>
> --
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