netdev - [PATCH net-XXX] mISDN: Fix a use after free in hfcmulti

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Message-ID: <8be65f5a-c2dd-4ba0-8a10-bfe5980b8cfb@stanley.mountain>
Date: Wed, 24 Jul 2024 11:08:18 -0500
From: Dan Carpenter <dan.carpenter@...aro.org>
To: Karsten Keil <kkeil@...e.de>
Cc: Karsten Keil <isdn@...ux-pingi.de>,
	Jeff Johnson <quic_jjohnson@...cinc.com>,
	Jakub Kicinski <kuba@...nel.org>, netdev@...r.kernel.org,
	kernel-janitors@...r.kernel.org
Subject: [PATCH net-XXX] mISDN: Fix a use after free in hfcmulti_tx()

Don't dereference *sp after calling dev_kfree_skb(*sp).

Fixes: af69fb3a8ffa ("Add mISDN HFC multiport driver")
Signed-off-by: Dan Carpenter <dan.carpenter@...aro.org>
---
 drivers/isdn/hardware/mISDN/hfcmulti.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/drivers/isdn/hardware/mISDN/hfcmulti.c b/drivers/isdn/hardware/mISDN/hfcmulti.c
index 0d2928d8aeae..e5a483fd9ad8 100644
--- a/drivers/isdn/hardware/mISDN/hfcmulti.c
+++ b/drivers/isdn/hardware/mISDN/hfcmulti.c
@@ -1901,7 +1901,7 @@ hfcmulti_dtmf(struct hfc_multi *hc)
 static void
 hfcmulti_tx(struct hfc_multi *hc, int ch)
 {
-	int i, ii, temp, len = 0;
+	int i, ii, temp, tmp_len, len = 0;
 	int Zspace, z1, z2; /* must be int for calculation */
 	int Fspace, f1, f2;
 	u_char *d;
@@ -2122,14 +2122,15 @@ hfcmulti_tx(struct hfc_multi *hc, int ch)
 		HFC_wait_nodebug(hc);
 	}
 
+	tmp_len = (*sp)->len;
 	dev_kfree_skb(*sp);
 	/* check for next frame */
 	if (bch && get_next_bframe(bch)) {
-		len = (*sp)->len;
+		len = tmp_len;
 		goto next_frame;
 	}
 	if (dch && get_next_dframe(dch)) {
-		len = (*sp)->len;
+		len = tmp_len;
 		goto next_frame;
 	}
 
-- 
2.43.0