[SRU][N][PATCH 1/1] mISDN: Fix a use after free in hfcmulti_tx()

[Koichiro Den]

From: Dan Carpenter <dan.carpenter at linaro.org>

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

Fixes: af69fb3a8ffa ("Add mISDN HFC multiport driver")
Signed-off-by: Dan Carpenter <dan.carpenter at linaro.org>
Reviewed-by: Simon Horman <horms at kernel.org>
Link: https://patch.msgid.link/8be65f5a-c2dd-4ba0-8a10-bfe5980b8cfb@stanley.mountain
Signed-off-by: Jakub Kicinski <kuba at kernel.org>
(cherry picked from commit 61ab751451f5ebd0b98e02276a44e23a10110402)
CVE-2024-42280
Signed-off-by: Koichiro Den <koichiro.den at canonical.com>
---
 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 2e5cb9dde3ec..44383cec1f47 100644
--- a/drivers/isdn/hardware/mISDN/hfcmulti.c
+++ b/drivers/isdn/hardware/mISDN/hfcmulti.c
@@ -1900,7 +1900,7 @@ 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;
@@ -2121,14 +2121,15 @@ 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