usb: mon: make mmapped memory read only

Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=2157698
Upstream Status: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=a659daf63d16aa883be42f3f34ff84235c302198
CVE: CVE-2022-43750

commit a659daf
Author: Tadeusz Struk <tadeusz.struk@linaro.org>
Date: Mon, 19 Sep 2022 14:59:57 -0700

  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: stable <stable@kernel.org>
  Fixes: 6f23ee1 ("USB: add binary API to usbmon")
  Suggested-by: PaX Team <pageexec@freemail.hu>	# for the VM_MAYRITE portion
  Link: https://syzkaller.appspot.com/bug?id=2eb1f35d6525fa4a74d75b4244971e5b1411c95a
  Reported-by: syzbot+23f57c5ae902429285d7@syzkaller.appspotmail.com
  Signed-off-by: Tadeusz Struk <tadeusz.struk@linaro.org>
  Link: https://lore.kernel.org/r/20220919215957.205681-1-tadeusz.struk@linaro.org
  Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Signed-off-by: Desnes Nunes <desnesn@redhat.com>

Author: Desnes Nunes

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);