| Message ID | 20200428143009.107645-1-stefanha@redhat.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [v2] virtio-blk: handle block_device_operations callbacks after hot unplug | expand |
On Tue, Apr 28, 2020 at 03:30:09PM +0100, Stefan Hajnoczi wrote: > A userspace process holding a file descriptor to a virtio_blk device can > still invoke block_device_operations after hot unplug. For example, a > program that has /dev/vdb open can call ioctl(HDIO_GETGEO) after hot > unplug to invoke virtblk_getgeo(). which causes what? a use after free? > > Introduce a reference count in struct virtio_blk so that its lifetime > covers both virtio_driver probe/remove and block_device_operations > open/release users. This ensures that block_device_operations functions > like virtblk_getgeo() can safely access struct virtio_blk. > > Add remove_mutex to prevent block_device_operations functions from > accessing vblk->vdev during virtblk_remove() and let the safely check let the -> let them? > for !vblk->vdev after virtblk_remove() returns. > > Switching to a reference count also solves the vd_index_ida leak where > vda, vdb, vdc, etc indices were lost when the device was hot unplugged > while the block device was still open. Can you move this statement up so we list both issues (use after free and leak) upfront, then discuss the fix? > > Reported-by: Lance Digby <ldigby@redhat.com> > Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com> > --- > If someone has a simpler solution please let me know. I looked at > various approaches including reusing device_lock(&vblk->vdev.dev) but > they were more complex and extending the lifetime of virtio_device after > remove() has been called seems questionable. > --- > drivers/block/virtio_blk.c | 85 ++++++++++++++++++++++++++++++++++---- > 1 file changed, 77 insertions(+), 8 deletions(-) > > diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c > index 93468b7c6701..3dd53b445cc1 100644 > --- a/drivers/block/virtio_blk.c > +++ b/drivers/block/virtio_blk.c > @@ -44,6 +44,13 @@ struct virtio_blk { > /* Process context for config space updates */ > struct work_struct config_work; > > + /* > + * Tracks references from block_device_operations open/release and > + * virtio_driver probe/remove so this object can be freed once no > + * longer in use. > + */ > + refcount_t refs; > + > /* What host tells us, plus 2 for header & tailer. */ > unsigned int sg_elems; > > @@ -53,6 +60,9 @@ struct virtio_blk { > /* num of vqs */ > int num_vqs; > struct virtio_blk_vq *vqs; > + > + /* Provides mutual exclusion with virtblk_remove(). */ This is not the best way to document access rules. Which fields does this protect, exactly? I think it's just vdev. Right? Pls add to the comment. > + struct mutex remove_mutex; > }; > > struct virtblk_req { > @@ -295,10 +305,54 @@ static int virtblk_get_id(struct gendisk *disk, char *id_str) > return err; > } > > +static void virtblk_get(struct virtio_blk *vblk) > +{ > + refcount_inc(&vblk->refs); > +} > + > +static void virtblk_put(struct virtio_blk *vblk) > +{ > + if (refcount_dec_and_test(&vblk->refs)) { > + ida_simple_remove(&vd_index_ida, vblk->index); > + mutex_destroy(&vblk->remove_mutex); > + kfree(vblk); > + } > +} > + > +static int virtblk_open(struct block_device *bd, fmode_t mode) > +{ > + struct virtio_blk *vblk = bd->bd_disk->private_data; > + int ret = -ENXIO; It's more common to do int ret = 0; and on error: ret = -ENXIO; let's do this. > + > + mutex_lock(&vblk->remove_mutex); > + > + if (vblk->vdev) { > + virtblk_get(vblk); > + ret = 0; > + } I prefer else ret = -ENXIO here. > + > + mutex_unlock(&vblk->remove_mutex); > + return ret; > +} > + > +static void virtblk_release(struct gendisk *disk, fmode_t mode) > +{ > + struct virtio_blk *vblk = disk->private_data; > + > + virtblk_put(vblk); > +} > + > /* We provide getgeo only to please some old bootloader/partitioning tools */ > static int virtblk_getgeo(struct block_device *bd, struct hd_geometry *geo) > { > struct virtio_blk *vblk = bd->bd_disk->private_data; > + int ret = -ENXIO; It's more common to do int ret = 0; and on error: ret = -ENXIO; let's do this. > + > + mutex_lock(&vblk->remove_mutex); > + > + if (!vblk->vdev) { > + goto out; > + } single lines are not supposed to use {}. if you add ret = -ENXIO here then it won't be a single line anymore though. > > /* see if the host passed in geometry config */ > if (virtio_has_feature(vblk->vdev, VIRTIO_BLK_F_GEOMETRY)) { > @@ -314,11 +368,17 @@ static int virtblk_getgeo(struct block_device *bd, struct hd_geometry *geo) > geo->sectors = 1 << 5; > geo->cylinders = get_capacity(bd->bd_disk) >> 11; > } > - return 0; > + > + ret = 0; > +out: > + mutex_unlock(&vblk->remove_mutex); > + return ret; > } > > static const struct block_device_operations virtblk_fops = { > .owner = THIS_MODULE, > + .open = virtblk_open, > + .release = virtblk_release, > .getgeo = virtblk_getgeo, > }; > > @@ -655,6 +715,10 @@ static int virtblk_probe(struct virtio_device *vdev) > goto out_free_index; > } > > + /* This reference is dropped in virtblk_remove(). */ > + refcount_set(&vblk->refs, 1); > + mutex_init(&vblk->remove_mutex); > + > vblk->vdev = vdev; > vblk->sg_elems = sg_elems; > > @@ -820,8 +884,12 @@ static int virtblk_probe(struct virtio_device *vdev) > static void virtblk_remove(struct virtio_device *vdev) > { > struct virtio_blk *vblk = vdev->priv; > - int index = vblk->index; > - int refc; > + > + /* > + * Virtqueue processing is stopped safely here but mutual exclusion is > + * needed for block_device_operations. > + */ > + mutex_lock(&vblk->remove_mutex); > > /* Make sure no work handler is accessing the device. */ > flush_work(&vblk->config_work); > @@ -834,15 +902,16 @@ static void virtblk_remove(struct virtio_device *vdev) > /* Stop all the virtqueues. */ > vdev->config->reset(vdev); > > - refc = kref_read(&disk_to_dev(vblk->disk)->kobj.kref); > + /* Virtqueue are stopped, nothing can use vblk->vdev anymore. */ Virtqueues? > + vblk->vdev = NULL; > + > put_disk(vblk->disk); > vdev->config->del_vqs(vdev); > kfree(vblk->vqs); > - kfree(vblk); > > - /* Only free device id if we don't have any users */ > - if (refc == 1) > - ida_simple_remove(&vd_index_ida, index); > + mutex_unlock(&vblk->remove_mutex); > + > + virtblk_put(vblk); > } > > #ifdef CONFIG_PM_SLEEP > -- > 2.25.3 >
On Tue, Apr 28, 2020 at 11:25:07AM -0400, Michael S. Tsirkin wrote: > On Tue, Apr 28, 2020 at 03:30:09PM +0100, Stefan Hajnoczi wrote: > > A userspace process holding a file descriptor to a virtio_blk device can > > still invoke block_device_operations after hot unplug. For example, a > > program that has /dev/vdb open can call ioctl(HDIO_GETGEO) after hot > > unplug to invoke virtblk_getgeo(). > > > which causes what? a use after free? Yes, use after free. I will include the kernel panic in the next revision. virtio_check_driver_offered_feature() accesses vdev->dev.driver, which doesn't work after virtblk_remove() has freed vdev :). > > > > Introduce a reference count in struct virtio_blk so that its lifetime > > covers both virtio_driver probe/remove and block_device_operations > > open/release users. This ensures that block_device_operations functions > > like virtblk_getgeo() can safely access struct virtio_blk. > > > > Add remove_mutex to prevent block_device_operations functions from > > accessing vblk->vdev during virtblk_remove() and let the safely check > > let the -> let them? Thanks, will fix. > > > for !vblk->vdev after virtblk_remove() returns. > > > > Switching to a reference count also solves the vd_index_ida leak where > > vda, vdb, vdc, etc indices were lost when the device was hot unplugged > > while the block device was still open. > > Can you move this statement up so we list both issues (use after free > and leak) upfront, then discuss the fix? Thanks, will fix. > > > > > Reported-by: Lance Digby <ldigby@redhat.com> > > Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com> > > --- > > If someone has a simpler solution please let me know. I looked at > > various approaches including reusing device_lock(&vblk->vdev.dev) but > > they were more complex and extending the lifetime of virtio_device after > > remove() has been called seems questionable. > > --- > > drivers/block/virtio_blk.c | 85 ++++++++++++++++++++++++++++++++++---- > > 1 file changed, 77 insertions(+), 8 deletions(-) > > > > diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c > > index 93468b7c6701..3dd53b445cc1 100644 > > --- a/drivers/block/virtio_blk.c > > +++ b/drivers/block/virtio_blk.c > > @@ -44,6 +44,13 @@ struct virtio_blk { > > /* Process context for config space updates */ > > struct work_struct config_work; > > > > + /* > > + * Tracks references from block_device_operations open/release and > > + * virtio_driver probe/remove so this object can be freed once no > > + * longer in use. > > + */ > > + refcount_t refs; > > + > > /* What host tells us, plus 2 for header & tailer. */ > > unsigned int sg_elems; > > > > @@ -53,6 +60,9 @@ struct virtio_blk { > > /* num of vqs */ > > int num_vqs; > > struct virtio_blk_vq *vqs; > > + > > + /* Provides mutual exclusion with virtblk_remove(). */ > > This is not the best way to document access rules. > Which fields does this protect, exactly? > I think it's just vdev. Right? > Pls add to the comment. Yes, vblk->vdev cannot be dereferenced after virtblk_remove() is entered. I'll document this mutex as protecting vdev. > > > + struct mutex remove_mutex; > > }; > > > > struct virtblk_req { > > @@ -295,10 +305,54 @@ static int virtblk_get_id(struct gendisk *disk, char *id_str) > > return err; > > } > > > > +static void virtblk_get(struct virtio_blk *vblk) > > +{ > > + refcount_inc(&vblk->refs); > > +} > > + > > +static void virtblk_put(struct virtio_blk *vblk) > > +{ > > + if (refcount_dec_and_test(&vblk->refs)) { > > + ida_simple_remove(&vd_index_ida, vblk->index); > > + mutex_destroy(&vblk->remove_mutex); > > + kfree(vblk); > > + } > > +} > > + > > +static int virtblk_open(struct block_device *bd, fmode_t mode) > > +{ > > + struct virtio_blk *vblk = bd->bd_disk->private_data; > > + int ret = -ENXIO; > > > It's more common to do > > int ret = 0; > > and on error: > ret = -ENXIO; > > > let's do this. Will fix. > > + > > + mutex_lock(&vblk->remove_mutex); > > + > > + if (vblk->vdev) { > > + virtblk_get(vblk); > > + ret = 0; > > + } > > I prefer > else > ret = -ENXIO > > here. Got it. > > + > > + mutex_unlock(&vblk->remove_mutex); > > + return ret; > > +} > > + > > +static void virtblk_release(struct gendisk *disk, fmode_t mode) > > +{ > > + struct virtio_blk *vblk = disk->private_data; > > + > > + virtblk_put(vblk); > > +} > > + > > /* We provide getgeo only to please some old bootloader/partitioning tools */ > > static int virtblk_getgeo(struct block_device *bd, struct hd_geometry *geo) > > { > > struct virtio_blk *vblk = bd->bd_disk->private_data; > > + int ret = -ENXIO; > > It's more common to do > > int ret = 0; > > and on error: > ret = -ENXIO; > > > let's do this. Will fix. > > > + > > + mutex_lock(&vblk->remove_mutex); > > + > > + if (!vblk->vdev) { > > + goto out; > > + } > > > single lines are not supposed to use {}. > if you add ret = -ENXIO here then it won't be a single line anymore > though. Oops, a QEMU coding style habit :). > > > > /* see if the host passed in geometry config */ > > if (virtio_has_feature(vblk->vdev, VIRTIO_BLK_F_GEOMETRY)) { > > @@ -314,11 +368,17 @@ static int virtblk_getgeo(struct block_device *bd, struct hd_geometry *geo) > > geo->sectors = 1 << 5; > > geo->cylinders = get_capacity(bd->bd_disk) >> 11; > > } > > - return 0; > > + > > + ret = 0; > > +out: > > + mutex_unlock(&vblk->remove_mutex); > > + return ret; > > } > > > > static const struct block_device_operations virtblk_fops = { > > .owner = THIS_MODULE, > > + .open = virtblk_open, > > + .release = virtblk_release, > > .getgeo = virtblk_getgeo, > > }; > > > > @@ -655,6 +715,10 @@ static int virtblk_probe(struct virtio_device *vdev) > > goto out_free_index; > > } > > > > + /* This reference is dropped in virtblk_remove(). */ > > + refcount_set(&vblk->refs, 1); > > + mutex_init(&vblk->remove_mutex); > > + > > vblk->vdev = vdev; > > vblk->sg_elems = sg_elems; > > > > @@ -820,8 +884,12 @@ static int virtblk_probe(struct virtio_device *vdev) > > static void virtblk_remove(struct virtio_device *vdev) > > { > > struct virtio_blk *vblk = vdev->priv; > > - int index = vblk->index; > > - int refc; > > + > > + /* > > + * Virtqueue processing is stopped safely here but mutual exclusion is > > + * needed for block_device_operations. > > + */ > > + mutex_lock(&vblk->remove_mutex); > > > > /* Make sure no work handler is accessing the device. */ > > flush_work(&vblk->config_work); > > @@ -834,15 +902,16 @@ static void virtblk_remove(struct virtio_device *vdev) > > /* Stop all the virtqueues. */ > > vdev->config->reset(vdev); > > > > - refc = kref_read(&disk_to_dev(vblk->disk)->kobj.kref); > > + /* Virtqueue are stopped, nothing can use vblk->vdev anymore. */ > > Virtqueues? Thanks, will fix.
On Tue, Apr 28, 2020 at 04:57:15PM +0100, Stefan Hajnoczi wrote: > On Tue, Apr 28, 2020 at 11:25:07AM -0400, Michael S. Tsirkin wrote: > > On Tue, Apr 28, 2020 at 03:30:09PM +0100, Stefan Hajnoczi wrote: > > > A userspace process holding a file descriptor to a virtio_blk device can > > > still invoke block_device_operations after hot unplug. For example, a > > > program that has /dev/vdb open can call ioctl(HDIO_GETGEO) after hot > > > unplug to invoke virtblk_getgeo(). > > > > > > which causes what? a use after free? > > Yes, use after free. I will include the kernel panic in the next > revision. > > virtio_check_driver_offered_feature() accesses vdev->dev.driver, which > doesn't work after virtblk_remove() has freed vdev :). > > > > > > > Introduce a reference count in struct virtio_blk so that its lifetime > > > covers both virtio_driver probe/remove and block_device_operations > > > open/release users. This ensures that block_device_operations functions > > > like virtblk_getgeo() can safely access struct virtio_blk. > > > > > > Add remove_mutex to prevent block_device_operations functions from > > > accessing vblk->vdev during virtblk_remove() and let the safely check > > > > let the -> let them? > > Thanks, will fix. > > > > > > for !vblk->vdev after virtblk_remove() returns. > > > > > > Switching to a reference count also solves the vd_index_ida leak where > > > vda, vdb, vdc, etc indices were lost when the device was hot unplugged > > > while the block device was still open. > > > > Can you move this statement up so we list both issues (use after free > > and leak) upfront, then discuss the fix? > > Thanks, will fix. Maybe add Fixes: if there's a specific commit that added geo support. > > > > > > > > Reported-by: Lance Digby <ldigby@redhat.com> > > > Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com> > > > --- > > > If someone has a simpler solution please let me know. I looked at > > > various approaches including reusing device_lock(&vblk->vdev.dev) but > > > they were more complex and extending the lifetime of virtio_device after > > > remove() has been called seems questionable. > > > --- > > > drivers/block/virtio_blk.c | 85 ++++++++++++++++++++++++++++++++++---- > > > 1 file changed, 77 insertions(+), 8 deletions(-) > > > > > > diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c > > > index 93468b7c6701..3dd53b445cc1 100644 > > > --- a/drivers/block/virtio_blk.c > > > +++ b/drivers/block/virtio_blk.c > > > @@ -44,6 +44,13 @@ struct virtio_blk { > > > /* Process context for config space updates */ > > > struct work_struct config_work; > > > > > > + /* > > > + * Tracks references from block_device_operations open/release and > > > + * virtio_driver probe/remove so this object can be freed once no > > > + * longer in use. > > > + */ > > > + refcount_t refs; > > > + > > > /* What host tells us, plus 2 for header & tailer. */ > > > unsigned int sg_elems; > > > > > > @@ -53,6 +60,9 @@ struct virtio_blk { > > > /* num of vqs */ > > > int num_vqs; > > > struct virtio_blk_vq *vqs; > > > + > > > + /* Provides mutual exclusion with virtblk_remove(). */ > > > > This is not the best way to document access rules. > > Which fields does this protect, exactly? > > I think it's just vdev. Right? > > Pls add to the comment. > > Yes, vblk->vdev cannot be dereferenced after virtblk_remove() is > entered. > > I'll document this mutex as protecting vdev. > > > > > > + struct mutex remove_mutex; > > > }; > > > > > > struct virtblk_req { > > > @@ -295,10 +305,54 @@ static int virtblk_get_id(struct gendisk *disk, char *id_str) > > > return err; > > > } > > > > > > +static void virtblk_get(struct virtio_blk *vblk) > > > +{ > > > + refcount_inc(&vblk->refs); > > > +} > > > + > > > +static void virtblk_put(struct virtio_blk *vblk) > > > +{ > > > + if (refcount_dec_and_test(&vblk->refs)) { > > > + ida_simple_remove(&vd_index_ida, vblk->index); > > > + mutex_destroy(&vblk->remove_mutex); > > > + kfree(vblk); > > > + } > > > +} > > > + > > > +static int virtblk_open(struct block_device *bd, fmode_t mode) > > > +{ > > > + struct virtio_blk *vblk = bd->bd_disk->private_data; > > > + int ret = -ENXIO; > > > > > > It's more common to do > > > > int ret = 0; > > > > and on error: > > ret = -ENXIO; > > > > > > let's do this. > > Will fix. > > > > + > > > + mutex_lock(&vblk->remove_mutex); > > > + > > > + if (vblk->vdev) { > > > + virtblk_get(vblk); > > > + ret = 0; > > > + } > > > > I prefer > > else > > ret = -ENXIO > > > > here. > > Got it. > > > > + > > > + mutex_unlock(&vblk->remove_mutex); > > > + return ret; > > > +} > > > + > > > +static void virtblk_release(struct gendisk *disk, fmode_t mode) > > > +{ > > > + struct virtio_blk *vblk = disk->private_data; > > > + > > > + virtblk_put(vblk); > > > +} > > > + > > > /* We provide getgeo only to please some old bootloader/partitioning tools */ > > > static int virtblk_getgeo(struct block_device *bd, struct hd_geometry *geo) > > > { > > > struct virtio_blk *vblk = bd->bd_disk->private_data; > > > + int ret = -ENXIO; > > > > It's more common to do > > > > int ret = 0; > > > > and on error: > > ret = -ENXIO; > > > > > > let's do this. > > Will fix. > > > > > > + > > > + mutex_lock(&vblk->remove_mutex); > > > + > > > + if (!vblk->vdev) { > > > + goto out; > > > + } > > > > > > single lines are not supposed to use {}. > > if you add ret = -ENXIO here then it won't be a single line anymore > > though. > > Oops, a QEMU coding style habit :). > > > > > > > /* see if the host passed in geometry config */ > > > if (virtio_has_feature(vblk->vdev, VIRTIO_BLK_F_GEOMETRY)) { > > > @@ -314,11 +368,17 @@ static int virtblk_getgeo(struct block_device *bd, struct hd_geometry *geo) > > > geo->sectors = 1 << 5; > > > geo->cylinders = get_capacity(bd->bd_disk) >> 11; > > > } > > > - return 0; > > > + > > > + ret = 0; > > > +out: > > > + mutex_unlock(&vblk->remove_mutex); > > > + return ret; > > > } > > > > > > static const struct block_device_operations virtblk_fops = { > > > .owner = THIS_MODULE, > > > + .open = virtblk_open, > > > + .release = virtblk_release, > > > .getgeo = virtblk_getgeo, > > > }; > > > > > > @@ -655,6 +715,10 @@ static int virtblk_probe(struct virtio_device *vdev) > > > goto out_free_index; > > > } > > > > > > + /* This reference is dropped in virtblk_remove(). */ > > > + refcount_set(&vblk->refs, 1); > > > + mutex_init(&vblk->remove_mutex); > > > + > > > vblk->vdev = vdev; > > > vblk->sg_elems = sg_elems; > > > > > > @@ -820,8 +884,12 @@ static int virtblk_probe(struct virtio_device *vdev) > > > static void virtblk_remove(struct virtio_device *vdev) > > > { > > > struct virtio_blk *vblk = vdev->priv; > > > - int index = vblk->index; > > > - int refc; > > > + > > > + /* > > > + * Virtqueue processing is stopped safely here but mutual exclusion is > > > + * needed for block_device_operations. > > > + */ > > > + mutex_lock(&vblk->remove_mutex); > > > > > > /* Make sure no work handler is accessing the device. */ > > > flush_work(&vblk->config_work); > > > @@ -834,15 +902,16 @@ static void virtblk_remove(struct virtio_device *vdev) > > > /* Stop all the virtqueues. */ > > > vdev->config->reset(vdev); > > > > > > - refc = kref_read(&disk_to_dev(vblk->disk)->kobj.kref); > > > + /* Virtqueue are stopped, nothing can use vblk->vdev anymore. */ > > > > Virtqueues? > > Thanks, will fix.
diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c index 93468b7c6701..3dd53b445cc1 100644 --- a/drivers/block/virtio_blk.c +++ b/drivers/block/virtio_blk.c @@ -44,6 +44,13 @@ struct virtio_blk { /* Process context for config space updates */ struct work_struct config_work; + /* + * Tracks references from block_device_operations open/release and + * virtio_driver probe/remove so this object can be freed once no + * longer in use. + */ + refcount_t refs; + /* What host tells us, plus 2 for header & tailer. */ unsigned int sg_elems; @@ -53,6 +60,9 @@ struct virtio_blk { /* num of vqs */ int num_vqs; struct virtio_blk_vq *vqs; + + /* Provides mutual exclusion with virtblk_remove(). */ + struct mutex remove_mutex; }; struct virtblk_req { @@ -295,10 +305,54 @@ static int virtblk_get_id(struct gendisk *disk, char *id_str) return err; } +static void virtblk_get(struct virtio_blk *vblk) +{ + refcount_inc(&vblk->refs); +} + +static void virtblk_put(struct virtio_blk *vblk) +{ + if (refcount_dec_and_test(&vblk->refs)) { + ida_simple_remove(&vd_index_ida, vblk->index); + mutex_destroy(&vblk->remove_mutex); + kfree(vblk); + } +} + +static int virtblk_open(struct block_device *bd, fmode_t mode) +{ + struct virtio_blk *vblk = bd->bd_disk->private_data; + int ret = -ENXIO; + + mutex_lock(&vblk->remove_mutex); + + if (vblk->vdev) { + virtblk_get(vblk); + ret = 0; + } + + mutex_unlock(&vblk->remove_mutex); + return ret; +} + +static void virtblk_release(struct gendisk *disk, fmode_t mode) +{ + struct virtio_blk *vblk = disk->private_data; + + virtblk_put(vblk); +} + /* We provide getgeo only to please some old bootloader/partitioning tools */ static int virtblk_getgeo(struct block_device *bd, struct hd_geometry *geo) { struct virtio_blk *vblk = bd->bd_disk->private_data; + int ret = -ENXIO; + + mutex_lock(&vblk->remove_mutex); + + if (!vblk->vdev) { + goto out; + } /* see if the host passed in geometry config */ if (virtio_has_feature(vblk->vdev, VIRTIO_BLK_F_GEOMETRY)) { @@ -314,11 +368,17 @@ static int virtblk_getgeo(struct block_device *bd, struct hd_geometry *geo) geo->sectors = 1 << 5; geo->cylinders = get_capacity(bd->bd_disk) >> 11; } - return 0; + + ret = 0; +out: + mutex_unlock(&vblk->remove_mutex); + return ret; } static const struct block_device_operations virtblk_fops = { .owner = THIS_MODULE, + .open = virtblk_open, + .release = virtblk_release, .getgeo = virtblk_getgeo, }; @@ -655,6 +715,10 @@ static int virtblk_probe(struct virtio_device *vdev) goto out_free_index; } + /* This reference is dropped in virtblk_remove(). */ + refcount_set(&vblk->refs, 1); + mutex_init(&vblk->remove_mutex); + vblk->vdev = vdev; vblk->sg_elems = sg_elems; @@ -820,8 +884,12 @@ static int virtblk_probe(struct virtio_device *vdev) static void virtblk_remove(struct virtio_device *vdev) { struct virtio_blk *vblk = vdev->priv; - int index = vblk->index; - int refc; + + /* + * Virtqueue processing is stopped safely here but mutual exclusion is + * needed for block_device_operations. + */ + mutex_lock(&vblk->remove_mutex); /* Make sure no work handler is accessing the device. */ flush_work(&vblk->config_work); @@ -834,15 +902,16 @@ static void virtblk_remove(struct virtio_device *vdev) /* Stop all the virtqueues. */ vdev->config->reset(vdev); - refc = kref_read(&disk_to_dev(vblk->disk)->kobj.kref); + /* Virtqueue are stopped, nothing can use vblk->vdev anymore. */ + vblk->vdev = NULL; + put_disk(vblk->disk); vdev->config->del_vqs(vdev); kfree(vblk->vqs); - kfree(vblk); - /* Only free device id if we don't have any users */ - if (refc == 1) - ida_simple_remove(&vd_index_ida, index); + mutex_unlock(&vblk->remove_mutex); + + virtblk_put(vblk); } #ifdef CONFIG_PM_SLEEP
A userspace process holding a file descriptor to a virtio_blk device can still invoke block_device_operations after hot unplug. For example, a program that has /dev/vdb open can call ioctl(HDIO_GETGEO) after hot unplug to invoke virtblk_getgeo(). Introduce a reference count in struct virtio_blk so that its lifetime covers both virtio_driver probe/remove and block_device_operations open/release users. This ensures that block_device_operations functions like virtblk_getgeo() can safely access struct virtio_blk. Add remove_mutex to prevent block_device_operations functions from accessing vblk->vdev during virtblk_remove() and let the safely check for !vblk->vdev after virtblk_remove() returns. Switching to a reference count also solves the vd_index_ida leak where vda, vdb, vdc, etc indices were lost when the device was hot unplugged while the block device was still open. Reported-by: Lance Digby <ldigby@redhat.com> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com> --- If someone has a simpler solution please let me know. I looked at various approaches including reusing device_lock(&vblk->vdev.dev) but they were more complex and extending the lifetime of virtio_device after remove() has been called seems questionable. --- drivers/block/virtio_blk.c | 85 ++++++++++++++++++++++++++++++++++---- 1 file changed, 77 insertions(+), 8 deletions(-)