Re: WARNING in request_end

[Dmitry Vyukov]

On Tue, Sep 25, 2018 at 11:18 AM, Kirill Tkhai <ktkhai@xxxxxxxxxxxxx> wrote:
> On 24.09.2018 17:44, Miklos Szeredi wrote:
>> On Mon, Sep 24, 2018 at 2:29 PM, syzbot
>> <syzbot+ef054c4d3f64cd7f7cec@xxxxxxxxxxxxxxxxxxxxxxxxx> 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@xxxxxxxxxxxxxxxxxxxxxxxxx
>>>
>>> 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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