netdev - [PATCH net-XXX] atm: idt77252: prevent use after free in dequeue

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Message-ID: <cd0308ff-fda4-405f-9854-6a3a75680da2@stanley.mountain>
Date: Fri, 9 Aug 2024 15:28:19 +0300
From: Dan Carpenter <dan.carpenter@...aro.org>
To: Chas Williams <3chas3@...il.com>
Cc: linux-atm-general@...ts.sourceforge.net, netdev@...r.kernel.org,
	kernel-janitors@...r.kernel.org
Subject: [PATCH net-XXX] atm: idt77252: prevent use after free in dequeue_rx()

We can't dereference "skb" after calling vcc->push() because the skb
is released.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Signed-off-by: Dan Carpenter <dan.carpenter@...aro.org>
---
 drivers/atm/idt77252.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/drivers/atm/idt77252.c b/drivers/atm/idt77252.c
index e7f713cd70d3..a876024d8a05 100644
--- a/drivers/atm/idt77252.c
+++ b/drivers/atm/idt77252.c
@@ -1118,8 +1118,8 @@ dequeue_rx(struct idt77252_dev *card, struct rsq_entry *rsqe)
 	rpp->len += skb->len;
 
 	if (stat & SAR_RSQE_EPDU) {
+		unsigned int len, truesize;
 		unsigned char *l1l2;
-		unsigned int len;
 
 		l1l2 = (unsigned char *) ((unsigned long) skb->data + skb->len - 6);
 
@@ -1189,14 +1189,15 @@ dequeue_rx(struct idt77252_dev *card, struct rsq_entry *rsqe)
 		ATM_SKB(skb)->vcc = vcc;
 		__net_timestamp(skb);
 
+		truesize = skb->truesize;
 		vcc->push(vcc, skb);
 		atomic_inc(&vcc->stats->rx);
 
-		if (skb->truesize > SAR_FB_SIZE_3)
+		if (truesize > SAR_FB_SIZE_3)
 			add_rx_skb(card, 3, SAR_FB_SIZE_3, 1);
-		else if (skb->truesize > SAR_FB_SIZE_2)
+		else if (truesize > SAR_FB_SIZE_2)
 			add_rx_skb(card, 2, SAR_FB_SIZE_2, 1);
-		else if (skb->truesize > SAR_FB_SIZE_1)
+		else if (truesize > SAR_FB_SIZE_1)
 			add_rx_skb(card, 1, SAR_FB_SIZE_1, 1);
 		else
 			add_rx_skb(card, 0, SAR_FB_SIZE_0, 1);
-- 
2.43.0