Re: [syzbot] kernel BUG in vhost_get_vq_desc

[Stefano Garzarella]

#syz test: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/
f71077a4d84b

Patch sent upstream:
https://lore.kernel.org/virtualization/20220221114916.107045-1-sgarzare@xxxxxxxxxx/T/#u

On Sun, Feb 20, 2022 at 3:11 AM syzbot
<syzbot+3140b17cb44a7b174008@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
>
> Hello,
>
> syzbot has tested the proposed patch and the reproducer did not trigger any issue:
>
> Reported-and-tested-by: syzbot+3140b17cb44a7b174008@xxxxxxxxxxxxxxxxxxxxxxxxx
>
> Tested on:
>
> commit:         f71077a4 Merge tag 'mmc-v5.17-rc1-2' of git://git.kern..
> git tree:       https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/
> kernel config:  https://syzkaller.appspot.com/x/.config?x=a78b064590b9f912
> dashboard link: https://syzkaller.appspot.com/bug?extid=3140b17cb44a7b174008
> compiler:       gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
> patch:          https://syzkaller.appspot.com/x/patch.diff?x=143dc0d4700000
>
> Note: testing is done by a robot and is best-effort only.
>
From 4951112bf98d3e10d3e9557986e5ca5419ca738f Mon Sep 17 00:00:00 2001
From: Stefano Garzarella <sgarzare@xxxxxxxxxx>
Date: Mon, 21 Feb 2022 11:07:49 +0100
Subject: [PATCH] vhost/vsock: don't check owner in vhost_vsock_stop() while
 releasing

vhost_vsock_stop() calls vhost_dev_check_owner() to check the device
ownership. It expects current->mm to be valid.

vhost_vsock_stop() is also called by vhost_vsock_dev_release() when
the user has not done close(), so when we are in do_exit(). In this
case current->mm is invalid and we're releasing the device, so we
should clean it anyway.

Let's check the owner only when vhost_vsock_stop() is called
by an ioctl.

Fixes: 433fc58e6bf2 ("VSOCK: Introduce vhost_vsock.ko")
Cc: stable@xxxxxxxxxxxxxxx
Reported-by: syzbot+1e3ea63db39f2b4440e0@xxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Stefano Garzarella <sgarzare@xxxxxxxxxx>
---
 drivers/vhost/vsock.c | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/drivers/vhost/vsock.c b/drivers/vhost/vsock.c
index d6ca1c7ad513..f00d2dfd72b7 100644
--- a/drivers/vhost/vsock.c
+++ b/drivers/vhost/vsock.c
@@ -629,16 +629,18 @@ static int vhost_vsock_start(struct vhost_vsock *vsock)
 	return ret;
 }
 
-static int vhost_vsock_stop(struct vhost_vsock *vsock)
+static int vhost_vsock_stop(struct vhost_vsock *vsock, bool check_owner)
 {
 	size_t i;
 	int ret;
 
 	mutex_lock(&vsock->dev.mutex);
 
-	ret = vhost_dev_check_owner(&vsock->dev);
-	if (ret)
-		goto err;
+	if (check_owner) {
+		ret = vhost_dev_check_owner(&vsock->dev);
+		if (ret)
+			goto err;
+	}
 
 	for (i = 0; i < ARRAY_SIZE(vsock->vqs); i++) {
 		struct vhost_virtqueue *vq = &vsock->vqs[i];
@@ -753,7 +755,7 @@ static int vhost_vsock_dev_release(struct inode *inode, struct file *file)
 	 * inefficient.  Room for improvement here. */
 	vsock_for_each_connected_socket(vhost_vsock_reset_orphans);
 
-	vhost_vsock_stop(vsock);
+	vhost_vsock_stop(vsock, false);
 	vhost_vsock_flush(vsock);
 	vhost_dev_stop(&vsock->dev);
 
@@ -868,7 +870,7 @@ static long vhost_vsock_dev_ioctl(struct file *f, unsigned int ioctl,
 		if (start)
 			return vhost_vsock_start(vsock);
 		else
-			return vhost_vsock_stop(vsock);
+			return vhost_vsock_stop(vsock, true);
 	case VHOST_GET_FEATURES:
 		features = VHOST_VSOCK_FEATURES;
 		if (copy_to_user(argp, &features, sizeof(features)))
-- 
2.35.1