virt: fix uninit-value in vhost_vsock_dev_open

[PATCH virt] virt: fix uninit-value in vhost_vsock_dev_open

Posted by Jeongjun Park 1 year, 9 months ago

Change vhost_vsock_dev_open() to use kvzalloc() instead of kvmalloc()
to avoid uninit state.

Reported-by: syzbot+6c21aeb59d0e82eb2782@syzkaller.appspotmail.com
Fixes: dcda9b04713c ("mm, tree wide: replace __GFP_REPEAT by __GFP_RETRY_MAYFAIL with more useful semantic")
Signed-off-by: Jeongjun Park <aha310510@gmail.com>
---
 drivers/vhost/vsock.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/vhost/vsock.c b/drivers/vhost/vsock.c
index ec20ecff85c7..652ef97a444b 100644
--- a/drivers/vhost/vsock.c
+++ b/drivers/vhost/vsock.c
@@ -656,7 +656,7 @@ static int vhost_vsock_dev_open(struct inode *inode, struct file *file)
 	/* This struct is large and allocation could fail, fall back to vmalloc
 	 * if there is no other way.
 	 */
-	vsock = kvmalloc(sizeof(*vsock), GFP_KERNEL | __GFP_RETRY_MAYFAIL);
+	vsock = kvzalloc(sizeof(*vsock), GFP_KERNEL | __GFP_RETRY_MAYFAIL);
 	if (!vsock)
 		return -ENOMEM;
 
-- 
2.34.1

Re: [PATCH virt] virt: fix uninit-value in vhost_vsock_dev_open

Posted by Michael S. Tsirkin 1 year, 9 months ago

On Sat, Apr 20, 2024 at 05:57:50PM +0900, Jeongjun Park wrote:
> Change vhost_vsock_dev_open() to use kvzalloc() instead of kvmalloc()
> to avoid uninit state.
> 
> Reported-by: syzbot+6c21aeb59d0e82eb2782@syzkaller.appspotmail.com
> Fixes: dcda9b04713c ("mm, tree wide: replace __GFP_REPEAT by __GFP_RETRY_MAYFAIL with more useful semantic")
> Signed-off-by: Jeongjun Park <aha310510@gmail.com>

What value exactly is used uninitialized?

> ---
>  drivers/vhost/vsock.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/vhost/vsock.c b/drivers/vhost/vsock.c
> index ec20ecff85c7..652ef97a444b 100644
> --- a/drivers/vhost/vsock.c
> +++ b/drivers/vhost/vsock.c
> @@ -656,7 +656,7 @@ static int vhost_vsock_dev_open(struct inode *inode, struct file *file)
>  	/* This struct is large and allocation could fail, fall back to vmalloc
>  	 * if there is no other way.
>  	 */
> -	vsock = kvmalloc(sizeof(*vsock), GFP_KERNEL | __GFP_RETRY_MAYFAIL);
> +	vsock = kvzalloc(sizeof(*vsock), GFP_KERNEL | __GFP_RETRY_MAYFAIL);
>  	if (!vsock)
>  		return -ENOMEM;
>  
> -- 
> 2.34.1

Re: [PATCH virt] virt: fix uninit-value in vhost_vsock_dev_open

Posted by Jeongjun Park 1 year, 9 months ago

static bool vhost_transport_seqpacket_allow(u32 remote_cid)
{
....
	vsock = vhost_vsock_get(remote_cid);

	if (vsock)
		seqpacket_allow = vsock->seqpacket_allow;
....
}

I think this is due to reading a previously created uninitialized 
vsock->seqpacket_allow inside vhost_transport_seqpacket_allow(), 
which is executed by the function pointer present in the if statement.

Thanks

Re: [PATCH virt] virt: fix uninit-value in vhost_vsock_dev_open

Posted by Stefan Hajnoczi 1 year, 9 months ago

On Sun, Apr 21, 2024 at 12:06:06PM +0900, Jeongjun Park wrote:
> static bool vhost_transport_seqpacket_allow(u32 remote_cid)
> {
> ....
> 	vsock = vhost_vsock_get(remote_cid);
> 
> 	if (vsock)
> 		seqpacket_allow = vsock->seqpacket_allow;
> ....
> }
> 
> I think this is due to reading a previously created uninitialized 
> vsock->seqpacket_allow inside vhost_transport_seqpacket_allow(), 
> which is executed by the function pointer present in the if statement.

CCing Arseny, author of commit ced7b713711f ("vhost/vsock: support
SEQPACKET for transport").

Looks like a genuine bug in the commit. vhost_vsock_set_features() sets
seqpacket_allow to true when the feature is negotiated. The assumption
is that the field defaults to false.

The rest of the vhost_vsock.ko code is written to initialize the
vhost_vsock fields, so you could argue seqpacket_allow should just be
explicitly initialized to false.

However, eliminating this class of errors by zeroing seems reasonable in
this code path. vhost_vsock_dev_open() is not performance-critical.

Acked-by: Stefan Hajnoczi <stefanha@redhat.com>

Re: [PATCH virt] virt: fix uninit-value in vhost_vsock_dev_open

Posted by Michael S. Tsirkin 1 year, 9 months ago

On Mon, Apr 22, 2024 at 09:00:31AM -0400, Stefan Hajnoczi wrote:
> On Sun, Apr 21, 2024 at 12:06:06PM +0900, Jeongjun Park wrote:
> > static bool vhost_transport_seqpacket_allow(u32 remote_cid)
> > {
> > ....
> > 	vsock = vhost_vsock_get(remote_cid);
> > 
> > 	if (vsock)
> > 		seqpacket_allow = vsock->seqpacket_allow;
> > ....
> > }
> > 
> > I think this is due to reading a previously created uninitialized 
> > vsock->seqpacket_allow inside vhost_transport_seqpacket_allow(), 
> > which is executed by the function pointer present in the if statement.
> 
> CCing Arseny, author of commit ced7b713711f ("vhost/vsock: support
> SEQPACKET for transport").
> 
> Looks like a genuine bug in the commit. vhost_vsock_set_features() sets
> seqpacket_allow to true when the feature is negotiated. The assumption
> is that the field defaults to false.
> 
> The rest of the vhost_vsock.ko code is written to initialize the
> vhost_vsock fields, so you could argue seqpacket_allow should just be
> explicitly initialized to false.
> 
> However, eliminating this class of errors by zeroing seems reasonable in
> this code path. vhost_vsock_dev_open() is not performance-critical.
> 
> Acked-by: Stefan Hajnoczi <stefanha@redhat.com>

But now that it's explained, the bugfix as proposed is incomplete:
userspace can set features twice and the second time will leak
old VIRTIO_VSOCK_F_SEQPACKET bit value.

And I am pretty sure the Fixes tag is wrong.

So I wrote this, but I actually don't have a set for
seqpacket to test this. Arseny could you help test maybe?
Thanks!

commit bcc17a060d93b198d8a17a9b87b593f41337ee28
Author: Michael S. Tsirkin <mst@redhat.com>
Date:   Mon Apr 22 10:03:13 2024 -0400

vhost/vsock: always initialize seqpacket_allow

There are two issues around seqpacket_allow:
1. seqpacket_allow is not initialized when socket is
created. Thus if features are never set, it will be
read uninitialized.
2. if VIRTIO_VSOCK_F_SEQPACKET is set and then cleared,
then seqpacket_allow will not be cleared appropriately
(existing apps I know about don't usually do this but
it's legal and there's no way to be sure no one relies
on this).

To fix:
    - initialize seqpacket_allow after allocation
    - set it unconditionally in set_features

Reported-by: syzbot+6c21aeb59d0e82eb2782@syzkaller.appspotmail.com
Reported-by: Jeongjun Park <aha310510@gmail.com>
Fixes: ced7b713711f ("vhost/vsock: support SEQPACKET for transport").
Cc: Arseny Krasnov <arseny.krasnov@kaspersky.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

diff --git a/drivers/vhost/vsock.c b/drivers/vhost/vsock.c
index ec20ecff85c7..bf664ec9341b 100644
--- a/drivers/vhost/vsock.c
+++ b/drivers/vhost/vsock.c
@@ -667,6 +667,7 @@ static int vhost_vsock_dev_open(struct inode *inode, struct file *file)
 	}

 	vsock->guest_cid = 0; /* no CID assigned yet */
+	vsock->seqpacket_allow = false;

 	atomic_set(&vsock->queued_replies, 0);

@@ -810,8 +811,7 @@ static int vhost_vsock_set_features(struct vhost_vsock *vsock, u64 features)
 			goto err;
 	}

-	if (features & (1ULL << VIRTIO_VSOCK_F_SEQPACKET))
-		vsock->seqpacket_allow = true;
+	vsock->seqpacket_allow = features & (1ULL << VIRTIO_VSOCK_F_SEQPACKET);

 	for (i = 0; i < ARRAY_SIZE(vsock->vqs); i++) {
 		vq = &vsock->vqs[i];

Re: [PATCH virt] virt: fix uninit-value in vhost_vsock_dev_open

Posted by Arseniy Krasnov 1 year, 9 months ago

> But now that it's explained, the bugfix as proposed is incomplete:
> userspace can set features twice and the second time will leak
> old VIRTIO_VSOCK_F_SEQPACKET bit value.
> 
> And I am pretty sure the Fixes tag is wrong.
> 
> So I wrote this, but I actually don't have a set for
> seqpacket to test this. Arseny could you help test maybe?
> Thanks!

Hi! Sorry for late reply! Just run vsock test suite with this patch -
seems everything is ok!

> 
> 
> commit bcc17a060d93b198d8a17a9b87b593f41337ee28
> Author: Michael S. Tsirkin <mst@redhat.com>
> Date:   Mon Apr 22 10:03:13 2024 -0400
> 
> vhost/vsock: always initialize seqpacket_allow
> 
> There are two issues around seqpacket_allow:
> 1. seqpacket_allow is not initialized when socket is
> created. Thus if features are never set, it will be
> read uninitialized.
> 2. if VIRTIO_VSOCK_F_SEQPACKET is set and then cleared,
> then seqpacket_allow will not be cleared appropriately
> (existing apps I know about don't usually do this but
> it's legal and there's no way to be sure no one relies
> on this).
> 
> To fix:
>     - initialize seqpacket_allow after allocation
>     - set it unconditionally in set_features
> 
> Reported-by: syzbot+6c21aeb59d0e82eb2782@syzkaller.appspotmail.com
> Reported-by: Jeongjun Park <aha310510@gmail.com>
> Fixes: ced7b713711f ("vhost/vsock: support SEQPACKET for transport").
> Cc: Arseny Krasnov <arseny.krasnov@kaspersky.com>
> Cc: David S. Miller <davem@davemloft.net>
> Cc: Stefan Hajnoczi <stefanha@redhat.com>
> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

Acked-by: Arseniy Krasnov <avkrasnov@salutedevices.com>

> 
> diff --git a/drivers/vhost/vsock.c b/drivers/vhost/vsock.c
> index ec20ecff85c7..bf664ec9341b 100644
> --- a/drivers/vhost/vsock.c
> +++ b/drivers/vhost/vsock.c
> @@ -667,6 +667,7 @@ static int vhost_vsock_dev_open(struct inode *inode, struct file *file)
>  	}
>  
>  	vsock->guest_cid = 0; /* no CID assigned yet */
> +	vsock->seqpacket_allow = false;
>  
>  	atomic_set(&vsock->queued_replies, 0);
>  
> @@ -810,8 +811,7 @@ static int vhost_vsock_set_features(struct vhost_vsock *vsock, u64 features)
>  			goto err;
>  	}
>  
> -	if (features & (1ULL << VIRTIO_VSOCK_F_SEQPACKET))
> -		vsock->seqpacket_allow = true;
> +	vsock->seqpacket_allow = features & (1ULL << VIRTIO_VSOCK_F_SEQPACKET);
>  
>  	for (i = 0; i < ARRAY_SIZE(vsock->vqs); i++) {
>  		vq = &vsock->vqs[i];