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Date:   Sat, 23 Nov 2019 09:18:16 -0800
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Message-ID: <0000000000004ef701059806b7f1@google.com>
Subject: Re: Re: Re: possible deadlock in mon_bin_vma_fault
From:   syzbot <syzbot+56f9673bb4cdcbeb0e92@syzkaller.appspotmail.com>
To:     Alan Stern <stern@rowland.harvard.edu>
Cc:     arnd@arndb.de, gregkh@linuxfoundation.org, jrdr.linux@gmail.com,
        keescook@chromium.org, kstewart@linuxfoundation.org,
        linux-kernel@vger.kernel.org, linux-usb@vger.kernel.org,
        stern@rowland.harvard.edu, syzkaller-bugs@googlegroups.com,
        tglx@linutronix.de, viro@zeniv.linux.org.uk, zaitcev@redhat.com
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Sender: linux-kernel-owner@vger.kernel.org
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> On Fri, 22 Nov 2019, syzbot wrote:

>> > #syz test: linux-4.19.y f6e27dbb1afa

>> "linux-4.19.y" does not look like a valid git repo address.

> Let's try again.  The "git tree" value in the original bug report was
> "upstream", so I'll use that even though it doesn't look like a valid
> git repo address either.

> Alan Stern

> #syz test: upstream f6e27dbb1afa

"upstream" does not look like a valid git repo address.


> commit 5252eb4c8297fedbf1c5f1e67da44efe00e6ef6b
> Author: Pete Zaitcev <zaitcev@kotori.zaitcev.us>
> Date:   Thu Nov 21 17:24:00 2019 -0600

>       usb: Fix a deadlock in usbmon between mmap and read

>       Signed-off-by: Pete Zaitcev <zaitcev@redhat.com>
>       Reported-by: syzbot+56f9673bb4cdcbeb0e92@syzkaller.appspotmail.com

> diff --git a/drivers/usb/mon/mon_bin.c b/drivers/usb/mon/mon_bin.c
> index ac2b4fcc265f..f48a23adbc35 100644
> --- a/drivers/usb/mon/mon_bin.c
> +++ b/drivers/usb/mon/mon_bin.c
> @@ -1039,12 +1039,18 @@ static long mon_bin_ioctl(struct file *file,  
> unsigned int cmd, unsigned long arg

>    		mutex_lock(&rp->fetch_lock);
>    		spin_lock_irqsave(&rp->b_lock, flags);
> -		mon_free_buff(rp->b_vec, rp->b_size/CHUNK_SIZE);
> -		kfree(rp->b_vec);
> -		rp->b_vec  = vec;
> -		rp->b_size = size;
> -		rp->b_read = rp->b_in = rp->b_out = rp->b_cnt = 0;
> -		rp->cnt_lost = 0;
> +		if (rp->mmap_active) {
> +			mon_free_buff(vec, size/CHUNK_SIZE);
> +			kfree(vec);
> +			ret = -EBUSY;
> +		} else {
> +			mon_free_buff(rp->b_vec, rp->b_size/CHUNK_SIZE);
> +			kfree(rp->b_vec);
> +			rp->b_vec  = vec;
> +			rp->b_size = size;
> +			rp->b_read = rp->b_in = rp->b_out = rp->b_cnt = 0;
> +			rp->cnt_lost = 0;
> +		}
>    		spin_unlock_irqrestore(&rp->b_lock, flags);
>    		mutex_unlock(&rp->fetch_lock);
>    		}
> @@ -1216,13 +1222,21 @@ mon_bin_poll(struct file *file, struct  
> poll_table_struct *wait)
>    static void mon_bin_vma_open(struct vm_area_struct *vma)
>    {
>    	struct mon_reader_bin *rp = vma->vm_private_data;
> +	unsigned long flags;
> +
> +	spin_lock_irqsave(&rp->b_lock, flags);
>    	rp->mmap_active++;
> +	spin_unlock_irqrestore(&rp->b_lock, flags);
>    }

>    static void mon_bin_vma_close(struct vm_area_struct *vma)
>    {
> +	unsigned long flags;
> +
>    	struct mon_reader_bin *rp = vma->vm_private_data;
> +	spin_lock_irqsave(&rp->b_lock, flags);
>    	rp->mmap_active--;
> +	spin_unlock_irqrestore(&rp->b_lock, flags);
>    }

>    /*
> @@ -1234,16 +1248,12 @@ static vm_fault_t mon_bin_vma_fault(struct  
> vm_fault *vmf)
>    	unsigned long offset, chunk_idx;
>    	struct page *pageptr;

> -	mutex_lock(&rp->fetch_lock);
>    	offset = vmf->pgoff << PAGE_SHIFT;
> -	if (offset >= rp->b_size) {
> -		mutex_unlock(&rp->fetch_lock);
> +	if (offset >= rp->b_size)
>    		return VM_FAULT_SIGBUS;
> -	}
>    	chunk_idx = offset / CHUNK_SIZE;
>    	pageptr = rp->b_vec[chunk_idx].pg;
>    	get_page(pageptr);
> -	mutex_unlock(&rp->fetch_lock);
>    	vmf->page = pageptr;
>    	return 0;
>    }