[PATCH 4.14 062/106] xen/blkfront: dont take local copy of a request from the ring page

Greg Kroah-Hartman
2021-12-06T15:20:02Z

From: Juergen Gross <jgross@suse.com>

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>
---
drivers/block/xen-blkfront.c | 25 +++++++++++++++----------
1 file changed, 15 insertions(+), 10 deletions(-)

--- a/drivers/block/xen-blkfront.c
+++ b/drivers/block/xen-blkfront.c
@@ -537,7 +537,7 @@ static unsigned long blkif_ring_get_requ
rinfo->shadow[id].status = REQ_WAITING;
rinfo->shadow[id].associated_id = NO_ASSOCIATED_ID;

- (*ring_req)->u.rw.id = id;
+ rinfo->shadow[id].req.u.rw.id = id;

return id;
}
@@ -545,11 +545,12 @@ static unsigned long blkif_ring_get_requ
static int blkif_queue_discard_req(struct request *req, struct blkfront_ring_info *rinfo)
{
struct blkfront_info *info = rinfo->dev_info;
- struct blkif_request *ring_req;
+ struct blkif_request *ring_req, *final_ring_req;
unsigned long id;

/* Fill out a communications ring structure. */
- id = blkif_ring_get_request(rinfo, req, &ring_req);
+ id = blkif_ring_get_request(rinfo, req, &final_ring_req);
+ ring_req = &rinfo->shadow[id].req;

ring_req->operation = BLKIF_OP_DISCARD;
ring_req->u.discard.nr_sectors = blk_rq_sectors(req);
@@ -560,8 +561,8 @@ static int blkif_queue_discard_req(struc
else
ring_req->u.discard.flag = 0;

- /* Keep a private copy so we can reissue requests when recovering. */
- rinfo->shadow[id].req = *ring_req;
+ /* Copy the request to the ring page. */
+ *final_ring_req = *ring_req;

return 0;
}
@@ -694,6 +695,7 @@ static int blkif_queue_rw_req(struct req
{
struct blkfront_info *info = rinfo->dev_info;
struct blkif_request *ring_req, *extra_ring_req = NULL;
+ struct blkif_request *final_ring_req, *final_extra_ring_req = NULL;
unsigned long id, extra_id = NO_ASSOCIATED_ID;
bool require_extra_req = false;
int i;
@@ -738,7 +740,8 @@ static int blkif_queue_rw_req(struct req
}

/* Fill out a communications ring structure. */
- id = blkif_ring_get_request(rinfo, req, &ring_req);
+ id = blkif_ring_get_request(rinfo, req, &final_ring_req);
+ ring_req = &rinfo->shadow[id].req;

num_sg = blk_rq_map_sg(req->q, req, rinfo->shadow[id].sg);
num_grant = 0;
@@ -789,7 +792,9 @@ static int blkif_queue_rw_req(struct req
ring_req->u.rw.nr_segments = num_grant;
if (unlikely(require_extra_req)) {
extra_id = blkif_ring_get_request(rinfo, req,
- &extra_ring_req);
+ &final_extra_ring_req);
+ extra_ring_req = &rinfo->shadow[extra_id].req;
+
/*
* Only the first request contains the scatter-gather
* list.
@@ -831,10 +836,10 @@ static int blkif_queue_rw_req(struct req
if (setup.segments)
kunmap_atomic(setup.segments);

- /* Keep a private copy so we can reissue requests when recovering. */
- rinfo->shadow[id].req = *ring_req;
+ /* Copy request(s) to the ring page. */
+ *final_ring_req = *ring_req;
if (unlikely(require_extra_req))
- rinfo->shadow[extra_id].req = *extra_ring_req;
+ *final_extra_ring_req = *extra_ring_req;

if (new_persistent_gnts)
gnttab_free_grant_references(setup.gref_head);