xen/blkfront: don't take local copy of a request from the ring page

commit 8f5a695d99000fc3aa73934d7ced33cfc64dcdab upstream.

In order to avoid a malicious backend being able to influence the local
copy of a request build the request locally first and then copy it to
the ring page instead of doing it the other way round as today.

Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Roger Pau Monné <roger.pau@citrix.com>
Link: https://lore.kernel.org/r/20210730103854.12681-3-jgross@suse.com
Signed-off-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
index abcb6b2e0e319a6f07d540642c2c56c70c087cf3..af027288cc23b70cbbb0d93ea575db4ed29a38d4 100644 (file)
--- a/drivers/block/xen-blkfront.c
+++ b/drivers/block/xen-blkfront.c
@@ -456,16 +456,31 @@ static int blkif_ioctl(struct block_device *bdev, fmode_t mode,
        return 0;
 }
 
+static unsigned long blkif_ring_get_request(struct blkfront_info *info,
+                                           struct request *req,
+                                           struct blkif_request **ring_req)
+{
+       unsigned long id;
+
+       *ring_req = RING_GET_REQUEST(&info->ring, info->ring.req_prod_pvt);
+       info->ring.req_prod_pvt++;
+
+       id = get_id_from_freelist(info);
+       info->shadow[id].request = req;
+       info->shadow[id].req.u.rw.id = id;
+
+       return id;
+}
+
 static int blkif_queue_discard_req(struct request *req)
 {
        struct blkfront_info *info = req->rq_disk->private_data;
-       struct blkif_request *ring_req;
+       struct blkif_request *ring_req, *final_ring_req;
        unsigned long id;
 
        /* Fill out a communications ring structure. */
-       ring_req = RING_GET_REQUEST(&info->ring, info->ring.req_prod_pvt);
-       id = get_id_from_freelist(info);
-       info->shadow[id].request = req;
+       id = blkif_ring_get_request(info, req, &final_ring_req);
+       ring_req = &info->shadow[id].req;
 
        ring_req->operation = BLKIF_OP_DISCARD;
        ring_req->u.discard.nr_sectors = blk_rq_sectors(req);
@@ -478,8 +493,8 @@ static int blkif_queue_discard_req(struct request *req)
 
        info->ring.req_prod_pvt++;
 
-       /* Keep a private copy so we can reissue requests when recovering. */
-       info->shadow[id].req = *ring_req;
+       /* Copy the request to the ring page. */
+       *final_ring_req = *ring_req;
 
        return 0;
 }
@@ -569,7 +584,7 @@ static void blkif_setup_rw_req_grant(unsigned long gfn, unsigned int offset,
 static int blkif_queue_rw_req(struct request *req)
 {
        struct blkfront_info *info = req->rq_disk->private_data;
-       struct blkif_request *ring_req;
+       struct blkif_request *ring_req, *final_ring_req;
        unsigned long id;
        int i;
        struct setup_rw_req setup = {
@@ -613,9 +628,8 @@ static int blkif_queue_rw_req(struct request *req)
                new_persistent_gnts = 0;
 
        /* Fill out a communications ring structure. */
-       ring_req = RING_GET_REQUEST(&info->ring, info->ring.req_prod_pvt);
-       id = get_id_from_freelist(info);
-       info->shadow[id].request = req;
+       id = blkif_ring_get_request(info, req, &final_ring_req);
+       ring_req = &info->shadow[id].req;
 
        BUG_ON(info->max_indirect_segments == 0 &&
               GREFS(req->nr_phys_segments) > BLKIF_MAX_SEGMENTS_PER_REQUEST);
@@ -696,8 +710,8 @@ static int blkif_queue_rw_req(struct request *req)
 
        info->ring.req_prod_pvt++;
 
-       /* Keep a private copy so we can reissue requests when recovering. */
-       info->shadow[id].req = *ring_req;
+       /* Copy request(s) to the ring page. */
+       *final_ring_req = *ring_req;
 
        if (new_persistent_gnts)
                gnttab_free_grant_references(setup.gref_head);