[2/6] vhost: validate MMU notifier registration
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Message ID 20190723075718.6275-3-jasowang@redhat.com
State New
Headers show
Series
  • Fixes for meta data acceleration
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Commit Message

Jason Wang July 23, 2019, 7:57 a.m. UTC
The return value of mmu_notifier_register() is not checked in
vhost_vring_set_num_addr(). This will cause an out of sync between mm
and MMU notifier thus a double free. To solve this, introduce a
boolean flag to track whether MMU notifier is registered and only do
unregistering when it was true.

Reported-and-tested-by:
syzbot+e58112d71f77113ddb7b@syzkaller.appspotmail.com
Fixes: 7f466032dc9e ("vhost: access vq metadata through kernel virtual address")
Signed-off-by: Jason Wang <jasowang@redhat.com>
---
 drivers/vhost/vhost.c | 19 +++++++++++++++----
 drivers/vhost/vhost.h |  1 +
 2 files changed, 16 insertions(+), 4 deletions(-)

Comments

Michael S. Tsirkin July 23, 2019, 9:17 a.m. UTC | #1
On Tue, Jul 23, 2019 at 03:57:14AM -0400, Jason Wang wrote:
> The return value of mmu_notifier_register() is not checked in
> vhost_vring_set_num_addr(). This will cause an out of sync between mm
> and MMU notifier thus a double free. To solve this, introduce a
> boolean flag to track whether MMU notifier is registered and only do
> unregistering when it was true.
> 
> Reported-and-tested-by:
> syzbot+e58112d71f77113ddb7b@syzkaller.appspotmail.com
> Fixes: 7f466032dc9e ("vhost: access vq metadata through kernel virtual address")
> Signed-off-by: Jason Wang <jasowang@redhat.com>

Right. This fixes the bug.
But it's not great that simple things like
setting vq address put pressure on memory allocator.
Also, if we get a single during processing
notifier register will fail, disabling optimization permanently.

In fact, see below:


> ---
>  drivers/vhost/vhost.c | 19 +++++++++++++++----
>  drivers/vhost/vhost.h |  1 +
>  2 files changed, 16 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> index 34c0d970bcbc..058191d5efad 100644
> --- a/drivers/vhost/vhost.c
> +++ b/drivers/vhost/vhost.c
> @@ -630,6 +630,7 @@ void vhost_dev_init(struct vhost_dev *dev,
>  	dev->iov_limit = iov_limit;
>  	dev->weight = weight;
>  	dev->byte_weight = byte_weight;
> +	dev->has_notifier = false;
>  	init_llist_head(&dev->work_list);
>  	init_waitqueue_head(&dev->wait);
>  	INIT_LIST_HEAD(&dev->read_list);
> @@ -731,6 +732,7 @@ long vhost_dev_set_owner(struct vhost_dev *dev)
>  	if (err)
>  		goto err_mmu_notifier;
>  #endif
> +	dev->has_notifier = true;
>  
>  	return 0;
>  

I just noticed that set owner now fails if we get a signal.
Userspace could retry in theory but it does not:
this is userspace abi breakage since it used to only
fail on invalid input.

> @@ -960,7 +962,11 @@ void vhost_dev_cleanup(struct vhost_dev *dev)
>  	}
>  	if (dev->mm) {
>  #if VHOST_ARCH_CAN_ACCEL_UACCESS
> -		mmu_notifier_unregister(&dev->mmu_notifier, dev->mm);
> +		if (dev->has_notifier) {
> +			mmu_notifier_unregister(&dev->mmu_notifier,
> +						dev->mm);
> +			dev->has_notifier = false;
> +		}
>  #endif
>  		mmput(dev->mm);
>  	}
> @@ -2065,8 +2071,10 @@ static long vhost_vring_set_num_addr(struct vhost_dev *d,
>  	/* Unregister MMU notifer to allow invalidation callback
>  	 * can access vq->uaddrs[] without holding a lock.
>  	 */
> -	if (d->mm)
> +	if (d->has_notifier) {
>  		mmu_notifier_unregister(&d->mmu_notifier, d->mm);
> +		d->has_notifier = false;
> +	}
>  
>  	vhost_uninit_vq_maps(vq);
>  #endif
> @@ -2086,8 +2094,11 @@ static long vhost_vring_set_num_addr(struct vhost_dev *d,
>  	if (r == 0)
>  		vhost_setup_vq_uaddr(vq);
>  
> -	if (d->mm)
> -		mmu_notifier_register(&d->mmu_notifier, d->mm);
> +	if (d->mm) {
> +		r = mmu_notifier_register(&d->mmu_notifier, d->mm);
> +		if (!r)
> +			d->has_notifier = true;
> +	}
>  #endif
>  
>  	mutex_unlock(&vq->mutex);
> diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h
> index 819296332913..a62f56a4cf72 100644
> --- a/drivers/vhost/vhost.h
> +++ b/drivers/vhost/vhost.h
> @@ -214,6 +214,7 @@ struct vhost_dev {
>  	int iov_limit;
>  	int weight;
>  	int byte_weight;
> +	bool has_notifier;
>  };
>  
>  bool vhost_exceeds_weight(struct vhost_virtqueue *vq, int pkts, int total_len);
> -- 
> 2.18.1
Jason Wang July 23, 2019, 1:30 p.m. UTC | #2
On 2019/7/23 下午5:17, Michael S. Tsirkin wrote:
> On Tue, Jul 23, 2019 at 03:57:14AM -0400, Jason Wang wrote:
>> The return value of mmu_notifier_register() is not checked in
>> vhost_vring_set_num_addr(). This will cause an out of sync between mm
>> and MMU notifier thus a double free. To solve this, introduce a
>> boolean flag to track whether MMU notifier is registered and only do
>> unregistering when it was true.
>>
>> Reported-and-tested-by:
>> syzbot+e58112d71f77113ddb7b@syzkaller.appspotmail.com
>> Fixes: 7f466032dc9e ("vhost: access vq metadata through kernel virtual address")
>> Signed-off-by: Jason Wang <jasowang@redhat.com>
> Right. This fixes the bug.
> But it's not great that simple things like
> setting vq address put pressure on memory allocator.
> Also, if we get a single during processing
> notifier register will fail, disabling optimization permanently.


Yes, but do we really care about this case. E.g we even fail for -ENOMEM 
for set owner.


>
> In fact, see below:
>
>
>> ---
>>   drivers/vhost/vhost.c | 19 +++++++++++++++----
>>   drivers/vhost/vhost.h |  1 +
>>   2 files changed, 16 insertions(+), 4 deletions(-)
>>
>> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
>> index 34c0d970bcbc..058191d5efad 100644
>> --- a/drivers/vhost/vhost.c
>> +++ b/drivers/vhost/vhost.c
>> @@ -630,6 +630,7 @@ void vhost_dev_init(struct vhost_dev *dev,
>>   	dev->iov_limit = iov_limit;
>>   	dev->weight = weight;
>>   	dev->byte_weight = byte_weight;
>> +	dev->has_notifier = false;
>>   	init_llist_head(&dev->work_list);
>>   	init_waitqueue_head(&dev->wait);
>>   	INIT_LIST_HEAD(&dev->read_list);
>> @@ -731,6 +732,7 @@ long vhost_dev_set_owner(struct vhost_dev *dev)
>>   	if (err)
>>   		goto err_mmu_notifier;
>>   #endif
>> +	dev->has_notifier = true;
>>   
>>   	return 0;
>>   
> I just noticed that set owner now fails if we get a signal.
> Userspace could retry in theory but it does not:
> this is userspace abi breakage since it used to only
> fail on invalid input.


Well, at least kthread_create() and vhost_dev_alloc_iovecs() will 
allocate memory.

Thanks


>
>> @@ -960,7 +962,11 @@ void vhost_dev_cleanup(struct vhost_dev *dev)
>>   	}
>>   	if (dev->mm) {
>>   #if VHOST_ARCH_CAN_ACCEL_UACCESS
>> -		mmu_notifier_unregister(&dev->mmu_notifier, dev->mm);
>> +		if (dev->has_notifier) {
>> +			mmu_notifier_unregister(&dev->mmu_notifier,
>> +						dev->mm);
>> +			dev->has_notifier = false;
>> +		}
>>   #endif
>>   		mmput(dev->mm);
>>   	}
>> @@ -2065,8 +2071,10 @@ static long vhost_vring_set_num_addr(struct vhost_dev *d,
>>   	/* Unregister MMU notifer to allow invalidation callback
>>   	 * can access vq->uaddrs[] without holding a lock.
>>   	 */
>> -	if (d->mm)
>> +	if (d->has_notifier) {
>>   		mmu_notifier_unregister(&d->mmu_notifier, d->mm);
>> +		d->has_notifier = false;
>> +	}
>>   
>>   	vhost_uninit_vq_maps(vq);
>>   #endif
>> @@ -2086,8 +2094,11 @@ static long vhost_vring_set_num_addr(struct vhost_dev *d,
>>   	if (r == 0)
>>   		vhost_setup_vq_uaddr(vq);
>>   
>> -	if (d->mm)
>> -		mmu_notifier_register(&d->mmu_notifier, d->mm);
>> +	if (d->mm) {
>> +		r = mmu_notifier_register(&d->mmu_notifier, d->mm);
>> +		if (!r)
>> +			d->has_notifier = true;
>> +	}
>>   #endif
>>   
>>   	mutex_unlock(&vq->mutex);
>> diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h
>> index 819296332913..a62f56a4cf72 100644
>> --- a/drivers/vhost/vhost.h
>> +++ b/drivers/vhost/vhost.h
>> @@ -214,6 +214,7 @@ struct vhost_dev {
>>   	int iov_limit;
>>   	int weight;
>>   	int byte_weight;
>> +	bool has_notifier;
>>   };
>>   
>>   bool vhost_exceeds_weight(struct vhost_virtqueue *vq, int pkts, int total_len);
>> -- 
>> 2.18.1

Patch
diff mbox series

diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index 34c0d970bcbc..058191d5efad 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -630,6 +630,7 @@  void vhost_dev_init(struct vhost_dev *dev,
 	dev->iov_limit = iov_limit;
 	dev->weight = weight;
 	dev->byte_weight = byte_weight;
+	dev->has_notifier = false;
 	init_llist_head(&dev->work_list);
 	init_waitqueue_head(&dev->wait);
 	INIT_LIST_HEAD(&dev->read_list);
@@ -731,6 +732,7 @@  long vhost_dev_set_owner(struct vhost_dev *dev)
 	if (err)
 		goto err_mmu_notifier;
 #endif
+	dev->has_notifier = true;
 
 	return 0;
 
@@ -960,7 +962,11 @@  void vhost_dev_cleanup(struct vhost_dev *dev)
 	}
 	if (dev->mm) {
 #if VHOST_ARCH_CAN_ACCEL_UACCESS
-		mmu_notifier_unregister(&dev->mmu_notifier, dev->mm);
+		if (dev->has_notifier) {
+			mmu_notifier_unregister(&dev->mmu_notifier,
+						dev->mm);
+			dev->has_notifier = false;
+		}
 #endif
 		mmput(dev->mm);
 	}
@@ -2065,8 +2071,10 @@  static long vhost_vring_set_num_addr(struct vhost_dev *d,
 	/* Unregister MMU notifer to allow invalidation callback
 	 * can access vq->uaddrs[] without holding a lock.
 	 */
-	if (d->mm)
+	if (d->has_notifier) {
 		mmu_notifier_unregister(&d->mmu_notifier, d->mm);
+		d->has_notifier = false;
+	}
 
 	vhost_uninit_vq_maps(vq);
 #endif
@@ -2086,8 +2094,11 @@  static long vhost_vring_set_num_addr(struct vhost_dev *d,
 	if (r == 0)
 		vhost_setup_vq_uaddr(vq);
 
-	if (d->mm)
-		mmu_notifier_register(&d->mmu_notifier, d->mm);
+	if (d->mm) {
+		r = mmu_notifier_register(&d->mmu_notifier, d->mm);
+		if (!r)
+			d->has_notifier = true;
+	}
 #endif
 
 	mutex_unlock(&vq->mutex);
diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h
index 819296332913..a62f56a4cf72 100644
--- a/drivers/vhost/vhost.h
+++ b/drivers/vhost/vhost.h
@@ -214,6 +214,7 @@  struct vhost_dev {
 	int iov_limit;
 	int weight;
 	int byte_weight;
+	bool has_notifier;
 };
 
 bool vhost_exceeds_weight(struct vhost_virtqueue *vq, int pkts, int total_len);