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@xxxxxxxxxxxxx>
---
drivers/scsi/libiscsi_tcp.c | 11 ++++++++---
1 file changed, 8 insertions(+), 3 deletions(-)
diff --git a/drivers/scsi/libiscsi_tcp.c b/drivers/scsi/libiscsi_tcp.c
index 8a6b1b3f8277..66d97d3bef5a 100644
--- 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) {
--
2.17.1
