From a659daf63d16aa883be42f3f34ff84235c302198 Mon Sep 17 00:00:00 2001
From: Tadeusz Struk <tadeusz.struk@linaro.org>
Date: Mon, 19 Sep 2022 14:59:57 -0700
Subject: [PATCH] usb: mon: make mmapped memory read only
Git-commit: a659daf63d16aa883be42f3f34ff84235c302198
References: bsc#1204653 CVE-2022-43750
Patch-mainline: v6.1-rc1
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: 6f23ee1fefdc ("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>
Acked-by: Takashi Iwai <tiwai@suse.de>
---
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);
--
2.35.3