On Thu, 30 Apr 2020 15:04:42 +0100
Stefan Hajnoczi <stefanha@xxxxxxxxxx> wrote:
> 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: 48e4043d4529523cbc7fa8dd745bd8e2c45ce1d3
> ("virtio: add virtio disk geometry feature")
Should be
Fixes: 48e4043d4529 ("virtio: add virtio disk geometry feature")
> Reported-by: Lance Digby <ldigby@xxxxxxxxxx>
> Signed-off-by: Stefan Hajnoczi <stefanha@xxxxxxxxxx>
> ---
> v4:
> * Clarify vdev_mutex usage [Stefano and Michael]
>
> 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 93468b7c6701..9d21bf0f155e 100644
> --- a/drivers/block/virtio_blk.c
> +++ b/drivers/block/virtio_blk.c
> @@ -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;
Using a struct kref might be more idiomatic.
> +
> /* What host tells us, plus 2 for header & tailer. */
> unsigned int sg_elems;
>
> @@ -295,10 +311,55 @@ 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);
Should the code even be able to grab a ref if !vblk->vdev?
> +}
> +
> +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);
I think that's where putting these cleanups into a release() funtion
would be more idiomatic.
> + }
> +}
(...)
Looks sane to me.
