[PATCH 4/7] IB/rxe: Do not copy extra stack memory to skb

From: Kees Cook
Date: Mon Jun 19 2017 - 16:27:31 EST

This fixes a over-read condition detected by FORTIFY_SOURCE for this line:

memcpy(SKB_TO_PKT(skb), &ack_pkt, sizeof(skb->cb));

The error was:

In file included from ./include/linux/bitmap.h:8:0,
from ./include/linux/cpumask.h:11,
from ./include/linux/mm_types_task.h:13,
from ./include/linux/mm_types.h:4,
from ./include/linux/kmemcheck.h:4,
from ./include/linux/skbuff.h:18,
from drivers/infiniband/sw/rxe/rxe_resp.c:34:
In function 'memcpy',
inlined from 'send_atomic_ack.constprop' at drivers/infiniband/sw/rxe/rxe_resp.c:998:2,
inlined from 'acknowledge' at drivers/infiniband/sw/rxe/rxe_resp.c:1026:3,
inlined from 'rxe_responder' at drivers/infiniband/sw/rxe/rxe_resp.c:1286:10:
./include/linux/string.h:309:4: error: call to '__read_overflow2' declared with attribute error: detected read beyond size of object passed as 2nd parameter

Daniel Micay noted that struct rxe_pkt_info is 32 bytes on 32-bit
architectures, but skb->cb is still 64. The memcpy() over-reads 32
bytes. This fixes it by zeroing the unused bytes in skb->cb.

Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
Cc: Moni Shoua <monis@xxxxxxxxxxxx>
Cc: Doug Ledford <dledford@xxxxxxxxxx>
Cc: Sean Hefty <sean.hefty@xxxxxxxxx>
Cc: Daniel Micay <danielmicay@xxxxxxxxx>
drivers/infiniband/sw/rxe/rxe_resp.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/infiniband/sw/rxe/rxe_resp.c b/drivers/infiniband/sw/rxe/rxe_resp.c
index 23039768f541..be944d5aa9af 100644
--- a/drivers/infiniband/sw/rxe/rxe_resp.c
+++ b/drivers/infiniband/sw/rxe/rxe_resp.c
@@ -995,7 +995,9 @@ static int send_atomic_ack(struct rxe_qp *qp, struct rxe_pkt_info *pkt,
free_rd_atomic_resource(qp, res);

- memcpy(SKB_TO_PKT(skb), &ack_pkt, sizeof(skb->cb));
+ memcpy(SKB_TO_PKT(skb), &ack_pkt, sizeof(ack_pkt));
+ memset((unsigned char *)SKB_TO_PKT(skb) + sizeof(ack_pkt), 0,
+ sizeof(skb->cb) - sizeof(ack_pkt));

res->type = RXE_ATOMIC_MASK;
res->atomic.skb = skb;