[PATCH v2] RDMA/rxe: Use validated num_sge in local buffer

[Nicolas Morey]

For both SRQ and non-SRQ receive paths, the WQE is copied into a local
buffer to provide a kernel-owned, validated copy. While calculating the
memcpy size from the validated num_sge prevents overflow during the
copy, memcpy() itself still copies num_sge from shared memory.

A concurrent userspace modification before or during memcpy() leaves
an unvalidated num_sge in the local buffer, leading to potential
out-of-bounds reads in rxe_resp_check_length() and copy_data() causing:

  BUG: KASAN: slab-out-of-bounds in rxe_receiver+0x8109/0x9ec0 [rdma_rxe]
  Read of size 4 at addr ffff88812c4867f8 by task kworker/u9:6/361
  Workqueue: rxe_wq do_work [rdma_rxe]
  Call Trace:
   rxe_receiver+0x8109/0x9ec0 [rdma_rxe]
   do_work+0x149/0x610 [rdma_rxe]
   process_one_work+0x726/0x10a0

  The buggy address belongs to the object at ffff88812c486000
   which belongs to the cache kmalloc-part-13-2k of size 2048
  The buggy address is located 0 bytes to the right of
   allocated 2040-byte region [ffff88812c486000, ffff88812c4867f8)

Explicitly assign the validated num_sge to the local buffer after the
copy to prevent this race.

Fixes: 22b8fbded65b ("RDMA/rxe: Fix TOCTOU heap overflow in get_srq_wqe")
Fixes: d6ab440240a0 ("RDMA/rxe: Copy WQE to local buffer in non-SRQ receive path")
Reviewed-by: Zhu Yanjun <yanjun.zhu@xxxxxxxxx>
Signed-off-by: Nicolas Morey <nmorey@xxxxxxxx>
---
v1 -> v2:
 - Added KASAN call trace to the commit log
 - Collected Reviewed-by tag.

 drivers/infiniband/sw/rxe/rxe_resp.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/infiniband/sw/rxe/rxe_resp.c b/drivers/infiniband/sw/rxe/rxe_resp.c
index 02b16e2b49b8..cd51042857d6 100644
--- a/drivers/infiniband/sw/rxe/rxe_resp.c
+++ b/drivers/infiniband/sw/rxe/rxe_resp.c
@@ -288,6 +288,7 @@ static enum resp_states get_srq_wqe(struct rxe_qp *qp)
 	}
 	size = sizeof(*wqe) + num_sge * sizeof(struct rxe_sge);
 	memcpy(&qp->resp.srq_wqe, wqe, size);
+	qp->resp.srq_wqe.wqe.dma.num_sge = num_sge;
 
 	qp->resp.wqe = &qp->resp.srq_wqe.wqe;
 	queue_advance_consumer(q, QUEUE_TYPE_FROM_CLIENT);
@@ -328,6 +329,7 @@ static enum resp_states rxe_get_recv_wqe(struct rxe_qp *qp)
 	}
 	size = sizeof(*wqe) + num_sge * sizeof(struct rxe_sge);
 	memcpy(&qp->resp.srq_wqe, wqe, size);
+	qp->resp.srq_wqe.wqe.dma.num_sge = num_sge;
 
 	qp->resp.wqe = &qp->resp.srq_wqe.wqe;
 	return RESPST_CHK_LENGTH;
-- 
2.54.0