From: Jan Beulich <jbeulich@suse.com>
Date: Tue, 13 Jun 2017 20:28:27 +0000 (-0400)
Subject: xen-blkback: don't leak stack data via response ring
X-Git-Tag: v3.2.91~5
X-Git-Url: https://git.openpandora.org/cgi-bin/gitweb.cgi?p=pandora-kernel.git;a=commitdiff_plain;h=cc21fe1ff77acfab555df5577ea46fc89932f3b2;hp=b8f254aa17f720053054c4ecff3920973a83b9d6

xen-blkback: don't leak stack data via response ring

commit 089bc0143f489bd3a4578bdff5f4ca68fb26f341 upstream.

Rather than constructing a local structure instance on the stack, fill
the fields directly on the shared ring, just like other backends do.
Build on the fact that all response structure flavors are actually
identical (the old code did make this assumption too).

This is XSA-216.


Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---

diff --git a/drivers/block/xen-blkback/blkback.c b/drivers/block/xen-blkback/blkback.c
index 2232b858618f..347aabc423ce 100644
--- a/drivers/block/xen-blkback/blkback.c
+++ b/drivers/block/xen-blkback/blkback.c
@@ -811,33 +811,34 @@ static int dispatch_rw_block_io(struct xen_blkif *blkif,
 static void make_response(struct xen_blkif *blkif, u64 id,
 			  unsigned short op, int st)
 {
-	struct blkif_response  resp;
+	struct blkif_response *resp;
 	unsigned long     flags;
 	union blkif_back_rings *blk_rings = &blkif->blk_rings;
 	int notify;
 
-	resp.id        = id;
-	resp.operation = op;
-	resp.status    = st;
-
 	spin_lock_irqsave(&blkif->blk_ring_lock, flags);
 	/* Place on the response ring for the relevant domain. */
 	switch (blkif->blk_protocol) {
 	case BLKIF_PROTOCOL_NATIVE:
-		memcpy(RING_GET_RESPONSE(&blk_rings->native, blk_rings->native.rsp_prod_pvt),
-		       &resp, sizeof(resp));
+		resp = RING_GET_RESPONSE(&blk_rings->native,
+					 blk_rings->native.rsp_prod_pvt);
 		break;
 	case BLKIF_PROTOCOL_X86_32:
-		memcpy(RING_GET_RESPONSE(&blk_rings->x86_32, blk_rings->x86_32.rsp_prod_pvt),
-		       &resp, sizeof(resp));
+		resp = RING_GET_RESPONSE(&blk_rings->x86_32,
+					 blk_rings->x86_32.rsp_prod_pvt);
 		break;
 	case BLKIF_PROTOCOL_X86_64:
-		memcpy(RING_GET_RESPONSE(&blk_rings->x86_64, blk_rings->x86_64.rsp_prod_pvt),
-		       &resp, sizeof(resp));
+		resp = RING_GET_RESPONSE(&blk_rings->x86_64,
+					 blk_rings->x86_64.rsp_prod_pvt);
 		break;
 	default:
 		BUG();
 	}
+
+	resp->id        = id;
+	resp->operation = op;
+	resp->status    = st;
+
 	blk_rings->common.rsp_prod_pvt++;
 	RING_PUSH_RESPONSES_AND_CHECK_NOTIFY(&blk_rings->common, notify);
 	spin_unlock_irqrestore(&blkif->blk_ring_lock, flags);
diff --git a/drivers/block/xen-blkback/common.h b/drivers/block/xen-blkback/common.h
index 2c6205e502ef..4a5f21e87a80 100644
--- a/drivers/block/xen-blkback/common.h
+++ b/drivers/block/xen-blkback/common.h
@@ -56,9 +56,6 @@
 struct blkif_common_request {
 	char dummy;
 };
-struct blkif_common_response {
-	char dummy;
-};
 
 /* i386 protocol version */
 #pragma pack(push, 4)
@@ -83,11 +80,6 @@ struct blkif_x86_32_request {
 		struct blkif_x86_32_request_discard discard;
 	} u;
 };
-struct blkif_x86_32_response {
-	uint64_t        id;              /* copied from request */
-	uint8_t         operation;       /* copied from request */
-	int16_t         status;          /* BLKIF_RSP_???       */
-};
 #pragma pack(pop)
 
 /* x86_64 protocol version */
@@ -112,18 +104,13 @@ struct blkif_x86_64_request {
 		struct blkif_x86_64_request_discard discard;
 	} u;
 };
-struct blkif_x86_64_response {
-	uint64_t       __attribute__((__aligned__(8))) id;
-	uint8_t         operation;       /* copied from request */
-	int16_t         status;          /* BLKIF_RSP_???       */
-};
 
 DEFINE_RING_TYPES(blkif_common, struct blkif_common_request,
-		  struct blkif_common_response);
+		  struct blkif_response);
 DEFINE_RING_TYPES(blkif_x86_32, struct blkif_x86_32_request,
-		  struct blkif_x86_32_response);
+		  struct blkif_response __packed);
 DEFINE_RING_TYPES(blkif_x86_64, struct blkif_x86_64_request,
-		  struct blkif_x86_64_response);
+		  struct blkif_response);
 
 union blkif_back_rings {
 	struct blkif_back_ring        native;