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 3.16: 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 c42c22e778d806b204f88b45fbc34d904d311f05..5bc220aefdd2e38ed8e6fa45a8cbff4ed494d909 100644 (file)
--- a/drivers/block/xen-blkback/blkback.c
+++ b/drivers/block/xen-blkback/blkback.c
@@ -1346,33 +1346,34 @@ 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 ef64f59921a7cf815efaf3c4ae104dc49122d5f4..62f6067f8f830a4cec7cbf144ab89688ffcf32a7 100644 (file)
--- a/drivers/block/xen-blkback/common.h
+++ b/drivers/block/xen-blkback/common.h
@@ -70,9 +70,8 @@
 struct blkif_common_request {
        char dummy;
 };
-struct blkif_common_response {
-       char dummy;
-};
+
+/* i386 protocol version */
 
 struct blkif_x86_32_request_rw {
        uint8_t        nr_segments;  /* number of segments                   */
@@ -124,14 +123,6 @@ struct blkif_x86_32_request {
        } u;
 } __attribute__((__packed__));
 
-/* i386 protocol version */
-#pragma pack(push, 4)
-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 */
 
 struct blkif_x86_64_request_rw {
@@ -188,18 +179,12 @@ struct blkif_x86_64_request {
        } u;
 } __attribute__((__packed__));
 
-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;