[PATCH] net: bnxt_en: Fix array overrun in bnxt_fill_l2_rewrite_fields()

[Olof Johansson <olof@lixom.net>]

This is caused by what seems to be a fragile typing approach by
the Broadcom firmware/driver:

/* FW expects smac to be in u16 array format */

So the driver uses eth_addr and eth_addr_mask as u16[6] instead of u8[12],
so the math in bnxt_fill_l2_rewrite_fields does a [6] deref of the u16
pointer, it goes out of bounds on the array.

Just a few lines below, they use ETH_ALEN/2, so this must have been
overlooked. I'm surprised original developers didn't notice the compiler
warnings?!

Fixes: 90f906243bf6 ("bnxt_en: Add support for L2 rewrite")
Signed-off-by: Olof Johansson <olof@lixom.net>
---
 drivers/net/ethernet/broadcom/bnxt/bnxt_tc.c | 25 ++++++++++++++-----------
 1 file changed, 14 insertions(+), 11 deletions(-)

diff --git a/drivers/net/ethernet/broadcom/bnxt/bnxt_tc.c b/drivers/net/ethernet/broadcom/bnxt/bnxt_tc.c
index 174412a55e53c..cde2b81f6fe54 100644
--- a/drivers/net/ethernet/broadcom/bnxt/bnxt_tc.c
+++ b/drivers/net/ethernet/broadcom/bnxt/bnxt_tc.c
@@ -149,29 +149,32 @@ static void bnxt_set_l2_key_mask(u32 part_key, u32 part_mask,
 
 static int
 bnxt_fill_l2_rewrite_fields(struct bnxt_tc_actions *actions,
-			    u16 *eth_addr, u16 *eth_addr_mask)
+			    u8 *eth_addr, u8 *eth_addr_mask)
 {
 	u16 *p;
+	u8 *am;
 	int j;
 
 	if (unlikely(bnxt_eth_addr_key_mask_invalid(eth_addr, eth_addr_mask)))
 		return -EINVAL;
 
-	if (!is_wildcard(&eth_addr_mask[0], ETH_ALEN)) {
-		if (!is_exactmatch(&eth_addr_mask[0], ETH_ALEN))
+	am = eth_addr_mask;
+	if (!is_wildcard(am, ETH_ALEN)) {
+		if (!is_exactmatch(am, ETH_ALEN))
 			return -EINVAL;
 		/* FW expects dmac to be in u16 array format */
-		p = eth_addr;
-		for (j = 0; j < 3; j++)
+		p = (u16 *)am;
+		for (j = 0; j < ETH_ALEN / 2; j++)
 			actions->l2_rewrite_dmac[j] = cpu_to_be16(*(p + j));
 	}
 
-	if (!is_wildcard(&eth_addr_mask[ETH_ALEN], ETH_ALEN)) {
-		if (!is_exactmatch(&eth_addr_mask[ETH_ALEN], ETH_ALEN))
+	am = eth_addr_mask + ETH_ALEN;
+	if (!is_wildcard(am, ETH_ALEN)) {
+		if (!is_exactmatch(am, ETH_ALEN))
 			return -EINVAL;
 		/* FW expects smac to be in u16 array format */
-		p = &eth_addr[ETH_ALEN / 2];
-		for (j = 0; j < 3; j++)
+		p = (u16 *)am;
+		for (j = 0; j < ETH_ALEN / 2; j++)
 			actions->l2_rewrite_smac[j] = cpu_to_be16(*(p + j));
 	}
 
@@ -285,12 +288,12 @@ static int bnxt_tc_parse_actions(struct bnxt *bp,
 	 * smac (6 bytes) if rewrite of both is specified, otherwise either
 	 * dmac or smac
 	 */
-	u16 eth_addr_mask[ETH_ALEN] = { 0 };
+	u8 eth_addr_mask[ETH_ALEN * 2] = { 0 };
 	/* Used to store the L2 rewrite key for dmac (6 bytes) followed by
 	 * smac (6 bytes) if rewrite of both is specified, otherwise either
 	 * dmac or smac
 	 */
-	u16 eth_addr[ETH_ALEN] = { 0 };
+	u8 eth_addr[ETH_ALEN * 2] = { 0 };
 	struct flow_action_entry *act;
 	int i, rc;
 
-- 
2.11.0