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SubjectRe: Re: Re: possible deadlock in mon_bin_vma_fault
From
> 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;
> }


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