bnxt: prevent skb UAF after handing over to PTP worker

When reading the timestamp is required bnxt_tx_int() hands over the ownership of the completed skb to the PTP worker. The skb should not be used afterwards, as the worker may run before the rest of our code and free the skb, leading to a use-after-free.

Since dev_kfree_skb_any() accepts NULL make the loss of ownership more obvious and set skb to NULL.

Fixes 83bb623c968e ("bnxt_en: Transmit and retrieve packet timestamps")

Signed-off-by Jakub Kicinski <[email protected]>

---
CC: [email protected]
CC: [email protected]
CC: [email protected]
CC: [email protected]

---
 drivers/net/ethernet/broadcom/bnxt/bnxt.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

drivers/net/ethernet/broadcom/bnxt/bnxt.c +5 -5

index f46eefb5a029..96da0ba3d507 100644
@@ -659,7 +659,6 @@ static void bnxt_tx_int(struct bnxt *bp, struct bnxt_napi *bnapi, int nr_pkts)
 
 	for (i = 0; i < nr_pkts; i++) {
 		struct bnxt_sw_tx_bd *tx_buf;
-		bool compl_deferred = false;
 		struct sk_buff *skb;
 		int j, last;
 

@@ -668,6 +667,8 @@ static void bnxt_tx_int(struct bnxt *bp, struct bnxt_napi *bnapi, int nr_pkts)
 		skb = tx_buf->skb;
 		tx_buf->skb = NULL;
 
+		tx_bytes += skb->len;
+
 		if (tx_buf->is_push) {
 			tx_buf->is_push = 0;
 			goto next_tx_int;

@@ -688,8 +689,9 @@ static void bnxt_tx_int(struct bnxt *bp, struct bnxt_napi *bnapi, int nr_pkts)
 		}
 		if (unlikely(skb_shinfo(skb)->tx_flags & SKBTX_IN_PROGRESS)) {
 			if (bp->flags & BNXT_FLAG_CHIP_P5) {
+				/* PTP worker takes ownership of the skb */
 				if (!bnxt_get_tx_ts_p5(bp, skb))
-					compl_deferred = true;
+					skb = NULL;
 				else
 					atomic_inc(&bp->ptp_cfg->tx_avail);
 			}

@@ -698,9 +700,7 @@ static void bnxt_tx_int(struct bnxt *bp, struct bnxt_napi *bnapi, int nr_pkts)
 next_tx_int:
 		cons = NEXT_TX(cons);
 
-		tx_bytes += skb->len;
-		if (!compl_deferred)
-			dev_kfree_skb_any(skb);
+		dev_kfree_skb_any(skb);
 	}
 
 	netdev_tx_completed_queue(txq, nr_pkts, tx_bytes);

Signature · 1 line

2.37.3

Quoted 9 lines · Jakub Kicinski

When reading the timestamp is required bnxt_tx_int() hands over the ownership of the completed skb to the PTP worker. The skb should not be used afterwards, as the worker may run before the rest of our code and free the skb, leading to a use-after-free.

Since dev_kfree_skb_any() accepts NULL make the loss of ownership more obvious and set skb to NULL.

Quoted 2 lines

Fixes 83bb623c968e ("bnxt_en: Transmit and retrieve packet timestamps")

Signed-off-by Jakub Kicinski <[email protected]>

In general this looks good to me. Let's make sure Pavan and Michael also agree. Thanks for the patch!

Reviewed-by Andy Gospodarek <[email protected]>