[PATCH v2] RDMA/mlx5: Use DEFINE_RAW_FLEX for leftovers flow attributes

[lirongqing <lirongqing@baidu.com>]

From: Li RongQing <lirongqing@baidu.com>

Commit e91fb8b9d0ed ("RDMA/mlx5: Avoid flexible array warning") split
the leftovers_specs[] array into two separate structs to silence the
sparse "array of flexible structures" warning, but in doing so reversed
the member order: eth_flow was placed before flow_attr.

_create_flow_rule() locates the flow specs with:

    ib_flow = (void *)flow_attr + sizeof(*flow_attr);

which expects the spec data to immediately follow the ib_flow_attr.
With the reversed order, flow_attr is the last member, so ib_flow
points past the end of the struct and the num_of_specs = 1 loop reads
out-of-bounds memory (whatever static data follows in the .data
section), producing incorrect flow rules or a crash.

Rebuild the leftovers attributes with DEFINE_RAW_FLEX(), which declares
an on-stack struct ib_flow_attr with a properly sized trailing flows[]
array.  The ETH spec lives in flows[0].eth at exactly the offset
_create_flow_rule() expects, so no layout-dependent composite struct is
needed.  This also avoids embedding a structure that contains a flexible
array member as a non-last member, which would trigger
-Wflex-array-member-not-at-end once the warning is enabled.

Fixes: e91fb8b9d0ed ("RDMA/mlx5: Avoid flexible array warning")
Signed-off-by: Li RongQing <lirongqing@baidu.com>
---
 drivers/infiniband/hw/mlx5/fs.c | 45 +++++++++++++++++++----------------------
 1 file changed, 21 insertions(+), 24 deletions(-)

diff --git a/drivers/infiniband/hw/mlx5/fs.c b/drivers/infiniband/hw/mlx5/fs.c
index 98cdc5c..e63fdb4 100644
--- a/drivers/infiniband/hw/mlx5/fs.c
+++ b/drivers/infiniband/hw/mlx5/fs.c
@@ -17,6 +17,7 @@
 #include <linux/mlx5/fs.h>
 #include <linux/mlx5/fs_helpers.h>
 #include <linux/mlx5/eswitch.h>
+#include <linux/overflow.h>
 #include <net/inet_ecn.h>
 #include "mlx5_ib.h"
 #include "counters.h"
@@ -1647,36 +1648,32 @@ static struct mlx5_ib_flow_handler *create_leftovers_rule(struct mlx5_ib_dev *de
 							  struct ib_flow_attr *flow_attr,
 							  struct mlx5_flow_destination *dst)
 {
+	DEFINE_RAW_FLEX(struct ib_flow_attr, flow_attr_wc, flows, 1);
+	DEFINE_RAW_FLEX(struct ib_flow_attr, flow_attr_uc, flows, 1);
+
 	struct mlx5_ib_flow_handler *handler_ucast = NULL;
 	struct mlx5_ib_flow_handler *handler = NULL;
 
-	static struct {
-		struct ib_flow_spec_eth eth_flow;
-		struct ib_flow_attr	flow_attr;
-	} leftovers_wc = { .flow_attr = { .num_of_specs = 1,
-					  .size = sizeof(leftovers_wc) },
-			   .eth_flow = {
-				   .type = IB_FLOW_SPEC_ETH,
-				   .size = sizeof(struct ib_flow_spec_eth),
-				   .mask = { .dst_mac = { 0x1 } },
-				   .val = { .dst_mac = { 0x1 } } } };
-
-	static struct {
-		struct ib_flow_spec_eth eth_flow;
-		struct ib_flow_attr	flow_attr;
-	} leftovers_uc = { .flow_attr = { .num_of_specs = 1,
-					  .size = sizeof(leftovers_uc) },
-			   .eth_flow = {
-				   .type = IB_FLOW_SPEC_ETH,
-				   .size = sizeof(struct ib_flow_spec_eth),
-				   .mask = { .dst_mac = { 0x1 } },
-				   .val = { .dst_mac = {} } } };
-
-	handler = create_flow_rule(dev, ft_prio, &leftovers_wc.flow_attr, dst);
+	flow_attr_wc->num_of_specs = 1;
+	flow_attr_wc->size = sizeof(struct ib_flow_attr) +
+			      sizeof(struct ib_flow_spec_eth);
+	flow_attr_wc->flows[0].eth.type = IB_FLOW_SPEC_ETH;
+	flow_attr_wc->flows[0].eth.size = sizeof(struct ib_flow_spec_eth);
+	flow_attr_wc->flows[0].eth.mask.dst_mac[0] = 0x1;
+	flow_attr_wc->flows[0].eth.val.dst_mac[0] = 0x1;
+
+	flow_attr_uc->num_of_specs = 1;
+	flow_attr_uc->size = sizeof(struct ib_flow_attr) +
+			      sizeof(struct ib_flow_spec_eth);
+	flow_attr_uc->flows[0].eth.type = IB_FLOW_SPEC_ETH;
+	flow_attr_uc->flows[0].eth.size = sizeof(struct ib_flow_spec_eth);
+	flow_attr_uc->flows[0].eth.mask.dst_mac[0] = 0x1;
+
+	handler = create_flow_rule(dev, ft_prio, flow_attr_wc, dst);
 	if (!IS_ERR(handler) &&
 	    flow_attr->type == IB_FLOW_ATTR_ALL_DEFAULT) {
 		handler_ucast = create_flow_rule(dev, ft_prio,
-						 &leftovers_uc.flow_attr, dst);
+						 flow_attr_uc, dst);
 		if (IS_ERR(handler_ucast)) {
 			mlx5_del_flow_rules(handler->rule);
 			ft_prio->refcount--;
-- 
2.9.4