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@xxxxxxxxxxxxxxxxxxxxxxxxx
Fixes: 7f466032dc9e ("vhost: access vq metadata through kernel virtual address")
Signed-off-by: Jason Wang <jasowang@xxxxxxxxxx>
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
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