[PATCH 1/1] usb: mon: make mmapped memory read only

[Yuxuan Luo]

From: Tadeusz Struk <tadeusz.struk at linaro.org>

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 at google.com>
Cc: stable <stable at kernel.org>
Fixes: 6f23ee1fefdc ("USB: add binary API to usbmon")
Suggested-by: PaX Team <pageexec at freemail.hu>	# for the VM_MAYRITE portion
Link: https://syzkaller.appspot.com/bug?id=2eb1f35d6525fa4a74d75b4244971e5b1411c95a
Reported-by: syzbot+23f57c5ae902429285d7 at syzkaller.appspotmail.com
Signed-off-by: Tadeusz Struk <tadeusz.struk at linaro.org>
Link: https://lore.kernel.org/r/20220919215957.205681-1-tadeusz.struk@linaro.org
Signed-off-by: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
(cherry picked from commit a659daf63d16aa883be42f3f34ff84235c302198)
CVE-2022-43750
Signed-off-by: Yuxuan Luo <yuxuan.luo at canonical.com>
---
 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);
-- 
2.34.1