Syzbot found an issue in usbmon module, where the user space client can corrupt the monitor's internal memory, causing the usbmon module to crash the kernel with segfault, UAF, etc. The reproducer mmaps the /dev/usbmon memory to user space, and overwrites it with arbitrary data, which causes all kinds of issues. Return an -EPERM error from mon_bin_mmap() if the flag VM_WRTIE is set. Also clear VM_MAYWRITE to make it impossible to change it to writable later.
Cc: "Dmitry Vyukov" dvyukov@google.com Cc: linux-usb@vger.kernel.org Cc: linux-kernel@vger.kernel.org Cc: stable@vger.kernel.org Fixes: 6f23ee1fefdc ("USB: add binary API to usbmon")
For the VM_MAYWRITE part: Suggested-by: PaX Team pageexec@freemail.hu
Link: https://syzkaller.appspot.com/bug?id=2eb1f35d6525fa4a74d75b4244971e5b1411c95... Reported-by: syzbot+23f57c5ae902429285d7@syzkaller.appspotmail.com Signed-off-by: Tadeusz Struk tadeusz.struk@linaro.org --- v2: Return an error instead of quietly clearing the flag, when VM_WRTIE is set. Also clear VM_MAYWRITE. --- drivers/usb/mon/mon_bin.c | 5 +++++ 1 file changed, 5 insertions(+)
diff --git a/drivers/usb/mon/mon_bin.c b/drivers/usb/mon/mon_bin.c index f48a23adbc35..094e812e9e69 100644 --- a/drivers/usb/mon/mon_bin.c +++ b/drivers/usb/mon/mon_bin.c @@ -1268,6 +1268,11 @@ static int mon_bin_mmap(struct file *filp, struct vm_area_struct *vma) { /* don't do anything here: "fault" will set up page table entries */ vma->vm_ops = &mon_bin_vm_ops; + + if (vma->vm_flags & VM_WRITE) + return -EPERM; + + vma->vm_flags &= ~VM_MAYWRITE; vma->vm_flags |= VM_DONTEXPAND | VM_DONTDUMP; vma->vm_private_data = filp->private_data; mon_bin_vma_open(vma);