[PATCH 5.6 021/194] virtio-blk: handle block_device_operations callbacks after hot unplug

Greg Kroah-Hartman
2020-05-18T18:01:34Z

From: Stefan Hajnoczi <stefanha@redhat.com>

[ Upstream commit 90b5feb8c4bebc76c27fcaf3e1a0e5ca2d319e9e ]

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: 48e4043d4529 ("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>
---
drivers/block/virtio_blk.c | 86 ++++++++++++++++++++++++++++++++++----
1 file changed, 78 insertions(+), 8 deletions(-)

diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
index 0736248999b0d..d52f33881ab6e 100644
--- a/drivers/block/virtio_blk.c
+++ b/drivers/block/virtio_blk.c
@@ -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. */
@@ -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;

@@ -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)) {
@@ -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,
};

@@ -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;

@@ -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);
@@ -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
--
2.20.1