usb: mon: Fix a deadlock in usbmon between mmap and read (19e6317d) · Commits · 戴 / test

The problem arises because our read() function grabs a lock of the circular buffer, finds something of interest, then invokes copy_to_user() straight from the buffer, which in turn takes mm->mmap_sem. In the same time, the callback mon_bin_vma_fault() is invoked under mm->mmap_sem. It attempts to take the fetch lock and deadlocks. This patch does away with protecting of our page list with any semaphores, and instead relies on the kernel not close the device while mmap is active in a process. In addition, we prohibit re-sizing of a buffer while mmap is active. This way, when (now unlocked) fault is processed, it works with the page that is intended to be mapped-in, and not some other random page. Note that this may have an ABI impact, but hopefully no legitimate program is this wrong. Signed-off-by:

Pete Zaitcev <zaitcev@redhat.com> Reported-by:

<syzbot+56f9673bb4cdcbeb0e92@syzkaller.appspotmail.com> Reviewed-by:

Alan Stern <stern@rowland.harvard.edu> Fixes: ("USB: fix usbmon BUG trigger") Cc: <stable@vger.kernel.org> Link: https://lore.kernel.org/r/20191204203941.3503452b@suzdal.zaitcev.lan Signed-off-by:

Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/mon/mon_bin.c

+21 −11

Original line number	Diff line number	Diff line
		@@ -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);
		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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