Re: [PATCH v2] virtio-blk: Avoid use-after-free on suspend/resume

Re: [PATCH v2] virtio-blk: Avoid use-after-free on suspend/resume

[Stefan Hajnoczi]

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On Thu, Aug 11, 2022 at 01:09:48AM +0900, Shigeru Yoshida wrote:
> hctx->user_data is set to vq in virtblk_init_hctx().  However, vq is
> freed on suspend and reallocated on resume.  So, hctx->user_data is
> invalid after resume, and it will cause use-after-free accessing which
> will result in the kernel crash something like below:
> 
> [   22.428391] Call Trace:
> [   22.428899]  <TASK>
> [   22.429339]  virtqueue_add_split+0x3eb/0x620
> [   22.430035]  ? __blk_mq_alloc_requests+0x17f/0x2d0
> [   22.430789]  ? kvm_clock_get_cycles+0x14/0x30
> [   22.431496]  virtqueue_add_sgs+0xad/0xd0
> [   22.432108]  virtblk_add_req+0xe8/0x150
> [   22.432692]  virtio_queue_rqs+0xeb/0x210
> [   22.433330]  blk_mq_flush_plug_list+0x1b8/0x280
> [   22.434059]  __blk_flush_plug+0xe1/0x140
> [   22.434853]  blk_finish_plug+0x20/0x40
> [   22.435512]  read_pages+0x20a/0x2e0
> [   22.436063]  ? folio_add_lru+0x62/0xa0
> [   22.436652]  page_cache_ra_unbounded+0x112/0x160
> [   22.437365]  filemap_get_pages+0xe1/0x5b0
> [   22.437964]  ? context_to_sid+0x70/0x100
> [   22.438580]  ? sidtab_context_to_sid+0x32/0x400
> [   22.439979]  filemap_read+0xcd/0x3d0
> [   22.440917]  xfs_file_buffered_read+0x4a/0xc0
> [   22.441984]  xfs_file_read_iter+0x65/0xd0
> [   22.442970]  __kernel_read+0x160/0x2e0
> [   22.443921]  bprm_execve+0x21b/0x640
> [   22.444809]  do_execveat_common.isra.0+0x1a8/0x220
> [   22.446008]  __x64_sys_execve+0x2d/0x40
> [   22.446920]  do_syscall_64+0x37/0x90
> [   22.447773]  entry_SYSCALL_64_after_hwframe+0x63/0xcd
> 
> This patch fixes this issue by getting vq from vblk, and removes
> virtblk_init_hctx().
> 
> Fixes: 4e0400525691 ("virtio-blk: support polling I/O")
> Cc: "Suwan Kim" <suwan.kim027@gmail.com>
> Signed-off-by: Shigeru Yoshida <syoshida@redhat.com>
> ---
>  drivers/block/virtio_blk.c | 24 ++++++++++--------------
>  1 file changed, 10 insertions(+), 14 deletions(-)

Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>

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Re: [PATCH v2] virtio-blk: Avoid use-after-free on suspend/resume

[Jens Axboe]

On 8/10/22 10:09 AM, Shigeru Yoshida wrote:
> +static inline struct virtio_blk_vq *get_virtio_blk_vq(struct blk_mq_hw_ctx *hctx)
> +{
> +	struct virtio_blk *vblk = hctx->queue->queuedata;
> +	struct virtio_blk_vq *vq = &vblk->vqs[hctx->queue_num];
> +
> +	return vq;
> +}

Would probably be cleaner as:

static struct virtio_blk_vq *get_virtio_blk_vq(struct blk_mq_hw_ctx *hctx)
{
	struct virtio_blk *vblk = hctx->queue->queuedata;

	return &vblk->vqs[hctx->queue_num];
}

dropping the 'vq' variable, and also dropping the inline as the compiler
will work that out anyway.

Apart from that minor nit, looks good to me.

-- 
Jens Axboe

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