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virtio-blk: handle block_device_operations callbacks after hot unplug
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[ Upstream commit 90b5feb ]

A userspace process holding a file descriptor to a virtio_blk device can
still invoke block_device_operations after hot unplug.  This leads to a
use-after-free accessing vblk->vdev in virtblk_getgeo() when
ioctl(HDIO_GETGEO) is invoked:

  BUG: unable to handle kernel NULL pointer dereference at 0000000000000090
  IP: [<ffffffffc00e5450>] virtio_check_driver_offered_feature+0x10/0x90 [virtio]
  PGD 800000003a92f067 PUD 3a930067 PMD 0
  Oops: 0000 [#1] SMP
  CPU: 0 PID: 1310 Comm: hdio-getgeo Tainted: G           OE  ------------   3.10.0-1062.el7.x86_64 #1
  Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.13.0-0-gf21b5a4aeb02-prebuilt.qemu.org 04/01/2014
  task: ffff9be5fbfb8000 ti: ffff9be5fa890000 task.ti: ffff9be5fa890000
  RIP: 0010:[<ffffffffc00e5450>]  [<ffffffffc00e5450>] virtio_check_driver_offered_feature+0x10/0x90 [virtio]
  RSP: 0018:ffff9be5fa893dc8  EFLAGS: 00010246
  RAX: ffff9be5fc3f3400 RBX: ffff9be5fa893e30 RCX: 0000000000000000
  RDX: 0000000000000000 RSI: 0000000000000004 RDI: ffff9be5fbc10b40
  RBP: ffff9be5fa893dc8 R08: 0000000000000301 R09: 0000000000000301
  R10: 0000000000000000 R11: 0000000000000000 R12: ffff9be5fdc24680
  R13: ffff9be5fbc10b40 R14: ffff9be5fbc10480 R15: 0000000000000000
  FS:  00007f1bfb968740(0000) GS:ffff9be5ffc00000(0000) knlGS:0000000000000000
  CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
  CR2: 0000000000000090 CR3: 000000003a894000 CR4: 0000000000360ff0
  DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
  DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
  Call Trace:
   [<ffffffffc016ac37>] virtblk_getgeo+0x47/0x110 [virtio_blk]
   [<ffffffff8d3f200d>] ? handle_mm_fault+0x39d/0x9b0
   [<ffffffff8d561265>] blkdev_ioctl+0x1f5/0xa20
   [<ffffffff8d488771>] block_ioctl+0x41/0x50
   [<ffffffff8d45d9e0>] do_vfs_ioctl+0x3a0/0x5a0
   [<ffffffff8d45dc81>] SyS_ioctl+0xa1/0xc0

A related problem is that virtblk_remove() leaks the vd_index_ida index
when something still holds a reference to vblk->disk during hot unplug.
This causes virtio-blk device names to be lost (vda, vdb, etc).

Fix these issues by protecting vblk->vdev with a mutex and reference
counting vblk so the vd_index_ida index can be removed in all cases.

Fixes: 48e4043 ("virtio: add virtio disk geometry feature")
Reported-by: Lance Digby <ldigby@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Link: https://lore.kernel.org/r/20200430140442.171016-1-stefanha@redhat.com
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
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@stefanhaRH @gregkh
stefanhaRH authored and gregkh committed May 20, 2020
1 parent 58530d9 commit b8c4c46
Showing 1 changed file with 78 additions and 8 deletions.
86 changes: 78 additions & 8 deletions drivers/block/virtio_blk.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -32,6 +32,15 @@ struct virtio_blk_vq {
} ____cacheline_aligned_in_smp;

struct virtio_blk {
/*
* This mutex must be held by anything that may run after
* virtblk_remove() sets vblk->vdev to NULL.
*
* blk-mq, virtqueue processing, and sysfs attribute code paths are
* shut down before vblk->vdev is set to NULL and therefore do not need
* to hold this mutex.
*/
struct mutex vdev_mutex;
struct virtio_device *vdev;

/* The disk structure for the kernel. */
Expand All @@ -43,6 +52,13 @@ 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;

Expand Down Expand Up @@ -294,10 +310,55 @@ 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->vdev_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 = 0;

mutex_lock(&vblk->vdev_mutex);

if (vblk->vdev)
virtblk_get(vblk);
else
ret = -ENXIO;

mutex_unlock(&vblk->vdev_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 = 0;

mutex_lock(&vblk->vdev_mutex);

if (!vblk->vdev) {
ret = -ENXIO;
goto out;
}

/* see if the host passed in geometry config */
if (virtio_has_feature(vblk->vdev, VIRTIO_BLK_F_GEOMETRY)) {
Expand All @@ -313,11 +374,15 @@ 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;
out:
mutex_unlock(&vblk->vdev_mutex);
return ret;
}

static const struct block_device_operations virtblk_fops = {
.owner = THIS_MODULE,
.open = virtblk_open,
.release = virtblk_release,
.getgeo = virtblk_getgeo,
};

Expand Down Expand Up @@ -657,6 +722,10 @@ 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->vdev_mutex);

vblk->vdev = vdev;
vblk->sg_elems = sg_elems;

Expand Down Expand Up @@ -822,8 +891,6 @@ 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;

/* Make sure no work handler is accessing the device. */
flush_work(&vblk->config_work);
Expand All @@ -833,18 +900,21 @@ static void virtblk_remove(struct virtio_device *vdev)

blk_mq_free_tag_set(&vblk->tag_set);

mutex_lock(&vblk->vdev_mutex);

/* Stop all the virtqueues. */
vdev->config->reset(vdev);

refc = kref_read(&disk_to_dev(vblk->disk)->kobj.kref);
/* Virtqueues 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->vdev_mutex);

virtblk_put(vblk);
}

#ifdef CONFIG_PM_SLEEP
Expand Down

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