Commit 90b5feb8 authored by Stefan Hajnoczi's avatar Stefan Hajnoczi Committed by Michael S. Tsirkin
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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.  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: 48e4043d ("virtio: add virtio disk geometry feature")
Reported-by: default avatarLance Digby <ldigby@redhat.com>
Signed-off-by: default avatarStefan Hajnoczi <stefanha@redhat.com>
Link: https://lore.kernel.org/r/20200430140442.171016-1-stefanha@redhat.com


Signed-off-by: default avatarMichael S. Tsirkin <mst@redhat.com>
Reviewed-by: default avatarStefano Garzarella <sgarzare@redhat.com>
parent 6a8b55ed

drivers/block/virtio_blk.c

+78 −8
Original line number Diff line number Diff line
@@ -33,6 +33,15 @@ 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. */
@@ -44,6 +53,13 @@ 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;
@@ -295,10 +311,55 @@ out: 
	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)) {
@@ -314,11 +375,15 @@ 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,

};
@@ -655,6 +720,10 @@ 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;
@@ -820,8 +889,6 @@ out: 
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);
@@ -831,18 +898,21 @@ 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

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