From facb5732b0bb59ebbc11b5d5abc249e677ddbeb6 Mon Sep 17 00:00:00 2001 From: Juergen Gross Date: Tue, 17 Feb 2015 08:02:47 +0100 Subject: [PATCH] xen-scsiback: mark pvscsi frontend request consumed only after last read A request in the ring buffer mustn't be read after it has been marked as consumed. Otherwise it might already have been reused by the frontend without violating the ring protocol. To avoid inconsistencies in the backend only work on a private copy of the request. This will ensure a malicious guest not being able to bypass consistency checks of the backend by modifying an active request. Signed-off-by: Juergen Gross Cc: Signed-off-by: David Vrabel --- drivers/xen/xen-scsiback.c | 14 ++++++-------- 1 file changed, 6 insertions(+), 8 deletions(-) diff --git a/drivers/xen/xen-scsiback.c b/drivers/xen/xen-scsiback.c index 61653a03a8f5..9faca6a60bb0 100644 --- a/drivers/xen/xen-scsiback.c +++ b/drivers/xen/xen-scsiback.c @@ -709,12 +709,11 @@ static int prepare_pending_reqs(struct vscsibk_info *info, static int scsiback_do_cmd_fn(struct vscsibk_info *info) { struct vscsiif_back_ring *ring = &info->ring; - struct vscsiif_request *ring_req; + struct vscsiif_request ring_req; struct vscsibk_pend *pending_req; RING_IDX rc, rp; int err, more_to_do; uint32_t result; - uint8_t act; rc = ring->req_cons; rp = ring->sring->req_prod; @@ -735,11 +734,10 @@ static int scsiback_do_cmd_fn(struct vscsibk_info *info) if (!pending_req) return 1; - ring_req = RING_GET_REQUEST(ring, rc); + ring_req = *RING_GET_REQUEST(ring, rc); ring->req_cons = ++rc; - act = ring_req->act; - err = prepare_pending_reqs(info, ring_req, pending_req); + err = prepare_pending_reqs(info, &ring_req, pending_req); if (err) { switch (err) { case -ENODEV: @@ -755,9 +753,9 @@ static int scsiback_do_cmd_fn(struct vscsibk_info *info) return 1; } - switch (act) { + switch (ring_req.act) { case VSCSIIF_ACT_SCSI_CDB: - if (scsiback_gnttab_data_map(ring_req, pending_req)) { + if (scsiback_gnttab_data_map(&ring_req, pending_req)) { scsiback_fast_flush_area(pending_req); scsiback_do_resp_with_sense(NULL, DRIVER_ERROR << 24, 0, pending_req); @@ -768,7 +766,7 @@ static int scsiback_do_cmd_fn(struct vscsibk_info *info) break; case VSCSIIF_ACT_SCSI_ABORT: scsiback_device_action(pending_req, TMR_ABORT_TASK, - ring_req->ref_rqid); + ring_req.ref_rqid); break; case VSCSIIF_ACT_SCSI_RESET: scsiback_device_action(pending_req, TMR_LUN_RESET, 0); -- 2.20.1