Re: [PATCH v2] virtio-blk: handle block_device_operations callbacks after hot unplug
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
> > > Signed-off-by: Stefan Hajnoczi
> > > ---
> > > If someone has a simpler solution please let me know. I looked at
> > > various approaches including reusing device_lock(>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(>refs);
> > > +}
> > > +
> > > +static void virtblk_put(struct virtio_blk *vblk)
> > > +{
> > > + if (refcount_dec_and_test(>refs)) {
> > > + ida_simple_remove(_index_ida, vblk->index);
> > > + mutex_destroy(>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(>remove_mutex);
> > > +
> > > + if (vblk->vdev) {
> > > + virtblk_get(vblk);
> > > + ret = 0;
> > > + }
> >
> > I prefer
> > else
> > ret = -ENXIO
> >
> > here.
>
> Got it.
>
> > > +
> > > + mutex_unlock(>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
Re: [PATCH v2] virtio-blk: handle block_device_operations callbacks after hot unplug
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
> > Signed-off-by: Stefan Hajnoczi
> > ---
> > If someone has a simpler solution please let me know. I looked at
> > various approaches including reusing device_lock(>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(>refs);
> > +}
> > +
> > +static void virtblk_put(struct virtio_blk *vblk)
> > +{
> > + if (refcount_dec_and_test(>refs)) {
> > + ida_simple_remove(_index_ida, vblk->index);
> > + mutex_destroy(>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(>remove_mutex);
> > +
> > + if (vblk->vdev) {
> > + virtblk_get(vblk);
> > + ret = 0;
> > + }
>
> I prefer
> else
> ret = -ENXIO
>
> here.
Got it.
> > +
> > + mutex_unlock(>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(>remove_mutex);
> > +
> > + if (!vblk->vdev) {
> > + goto out;
> > + }
>
>
>
Re: [PATCH v2] virtio-blk: handle block_device_operations callbacks after hot unplug
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
> Signed-off-by: Stefan Hajnoczi
> ---
> If someone has a simpler solution please let me know. I looked at
> various approaches including reusing device_lock(>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(>refs);
> +}
> +
> +static void virtblk_put(struct virtio_blk *vblk)
> +{
> + if (refcount_dec_and_test(>refs)) {
> + ida_simple_remove(_index_ida, vblk->index);
> + mutex_destroy(>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(>remove_mutex);
> +
> + if (vblk->vdev) {
> + virtblk_get(vblk);
> + ret = 0;
> + }
I prefer
else
ret = -ENXIO
here.
> +
> + mutex_unlock(>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(>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(>remove_mutex);
> + return ret;
> }
>
> static const struct block_device_operations virtblk_fops = {
> .owner = THIS_MODULE,
> + .open =
[PATCH v2] virtio-blk: handle block_device_operations callbacks after hot unplug
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
Signed-off-by: Stefan Hajnoczi
---
If someone has a simpler solution please let me know. I looked at
various approaches including reusing device_lock(>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(). */
+ 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(>refs);
+}
+
+static void virtblk_put(struct virtio_blk *vblk)
+{
+ if (refcount_dec_and_test(>refs)) {
+ ida_simple_remove(_index_ida, vblk->index);
+ mutex_destroy(>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(>remove_mutex);
+
+ if (vblk->vdev) {
+ virtblk_get(vblk);
+ ret = 0;
+ }
+
+ mutex_unlock(>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(>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(>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(>refs, 1);
+ mutex_init(>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(>remove_mutex);
/* Make sure no work handler is accessing the device. */
flush_work(>config_work);
@@ -834,15
