On Fri, Nov 22, 2019 at 12:38 AM Pete Zaitcev <zaitcev@xxxxxxxxxx> wrote:
>
> On Thu, 21 Nov 2019 11:20:20 -0500 (EST)
> Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> wrote:
>
> > On Thu, 21 Nov 2019, Pete Zaitcev wrote:
> >
> > > Anyway... If you are looking at it too, what do you think about not using
> > > any locks in mon_bin_vma_fault() at all? Isn't it valid? I think I tried
> > > to be "safe", but it only uses things that are constants unless we're
> > > opening and closing; a process cannot make page faults unless it has
> > > some thing mapped; and that is only possible if device is open and stays
> > > open. Can you find a hole in this reasoning?
> >
> > I think you're right. [...]
>
> How about the appended patch, then? You like?
>
> Do you happen to know how to refer to a syzbot report in a commit message?
>
> -- Pete
>
> commit 628f3bbf37eee21cce4cfbfaa6a796b129d7736d
> Author: Pete Zaitcev <zaitcev@xxxxxxxxxxxxxxxxx>
> 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@xxxxxxxxxx>
/\/\/\/\/\/\/\/\/\/\
Please don't forget the Reported-by
> diff --git a/drivers/usb/mon/mon_bin.c b/drivers/usb/mon/mon_bin.c
> index ac2b4fcc265f..fb7df9810bad 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);
> }
> @@ -1093,11 +1099,11 @@ static long mon_bin_ioctl(struct file *file, unsigned int cmd, unsigned long arg
> return ret;
> if (put_user(ret, &uptr->nfetch))
> return -EFAULT;
> - ret = 0;
> }
> break;
>
> - case MON_IOCG_STATS: {
> + case MON_IOCG_STATS:
> + {
> struct mon_bin_stats __user *sp;
> unsigned int nevents;
> unsigned int ndropped;
> @@ -1113,7 +1119,6 @@ static long mon_bin_ioctl(struct file *file, unsigned int cmd, unsigned long arg
> return -EFAULT;
> if (put_user(nevents, &sp->queued))
> return -EFAULT;
> -
> }
> break;
>
> @@ -1216,13 +1221,21 @@ 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 +1247,12 @@ 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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