virtio-blk: Avoid use-after-free on suspend/resume

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: 4e040052 ("virtio-blk: support polling I/O")
Cc: "Suwan Kim" <suwan.kim027@gmail.com>
Signed-off-by: Shigeru Yoshida <syoshida@redhat.com>
Message-Id: <20220810160948.959781-1-syoshida@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

drivers/block/virtio_blk.c

@@ -101,6 +101,14 @@ static inline blk_status_t virtblk_result(struct virtblk_req *vbr)
 	}
 }
 
+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;
+}
+
 static int virtblk_add_req(struct virtqueue *vq, struct virtblk_req *vbr)
 {
 	struct scatterlist hdr, status, *sgs[3];
@@ -416,7 +424,7 @@ static void virtio_queue_rqs(struct request **rqlist)
 	struct request *requeue_list = NULL;
 
 	rq_list_for_each_safe(rqlist, req, next) {
-		struct virtio_blk_vq *vq = req->mq_hctx->driver_data;
+		struct virtio_blk_vq *vq = get_virtio_blk_vq(req->mq_hctx);
 		bool kick;
 
 		if (!virtblk_prep_rq_batch(req)) {
@@ -837,7 +845,7 @@ static void virtblk_complete_batch(struct io_comp_batch *iob)
 static int virtblk_poll(struct blk_mq_hw_ctx *hctx, struct io_comp_batch *iob)
 {
 	struct virtio_blk *vblk = hctx->queue->queuedata;
-	struct virtio_blk_vq *vq = hctx->driver_data;
+	struct virtio_blk_vq *vq = get_virtio_blk_vq(hctx);
 	struct virtblk_req *vbr;
 	unsigned long flags;
 	unsigned int len;
@@ -862,22 +870,10 @@ static int virtblk_poll(struct blk_mq_hw_ctx *hctx, struct io_comp_batch *iob)
 	return found;
 }
 
-static int virtblk_init_hctx(struct blk_mq_hw_ctx *hctx, void *data,
-			  unsigned int hctx_idx)
-{
-	struct virtio_blk *vblk = data;
-	struct virtio_blk_vq *vq = &vblk->vqs[hctx_idx];
-
-	WARN_ON(vblk->tag_set.tags[hctx_idx] != hctx->tags);
-	hctx->driver_data = vq;
-	return 0;
-}
-
 static const struct blk_mq_ops virtio_mq_ops = {
 	.queue_rq	= virtio_queue_rq,
 	.queue_rqs	= virtio_queue_rqs,
 	.commit_rqs	= virtio_commit_rqs,
-	.init_hctx	= virtblk_init_hctx,
 	.complete	= virtblk_request_done,
 	.map_queues	= virtblk_map_queues,
 	.poll		= virtblk_poll,