scsi: libiscsi: fall back to sendmsg for slab pages

In "XFS over network block device" scenario XFS can create IO requests with
slab-based XFS metadata. During processing such requests tcp_sendpage() can
merge skb fragments with neighbour slab objects.

If receiving side is located on the same host tcp_recvmsg() can trigger
BUG_ON in hardening check and crash the host with following message:

usercopy: kernel memory exposure attempt detected
		from XXXXXXXX (kmalloc-512) (1024 bytes)

This patch redirect such requests from sednpage to sendmsg path.  The
problem is similar to one described in recent commit 7e241f647dc7
("libceph: fall back to sendmsg for slab pages")

Signed-off-by: Vasily Averin <vvs@virtuozzo.com>
Acked-by: Chris Leech <cleech@redhat.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

diff --git a/drivers/scsi/libiscsi_tcp.c b/drivers/scsi/libiscsi_tcp.c
index 9923e9e..c3fe3f3 100644 (file)
--- a/drivers/scsi/libiscsi_tcp.c
+++ b/drivers/scsi/libiscsi_tcp.c
@@ -129,12 +129,17 @@ static void iscsi_tcp_segment_map(struct iscsi_segment *segment, int recv)
        BUG_ON(sg->length == 0);
 
        /*
+        * We always map for the recv path.
+        *
         * If the page count is greater than one it is ok to send
         * to the network layer's zero copy send path. If not we
-        * have to go the slow sendmsg path. We always map for the
-        * recv path.
+        * have to go the slow sendmsg path.
+        *
+        * Same goes for slab pages: skb_can_coalesce() allows
+        * coalescing neighboring slab objects into a single frag which
+        * triggers one of hardened usercopy checks.
         */
-       if (page_count(sg_page(sg)) >= 1 && !recv)
+       if (!recv && page_count(sg_page(sg)) >= 1 && !PageSlab(sg_page(sg)))
                return;
 
        if (recv) {