linux-kernel - Re: [syzbot]

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Message-ID: <20250407141705.92770-1-contact@arnaud-lcm.com>
Date: Mon,  7 Apr 2025 16:17:05 +0200
From: Arnaud Lecomte <contact@...aud-lcm.com>
To: syzbot+29fc8991b0ecb186cf40@...kaller.appspotmail.com
Cc: andrew+netdev@...n.ch,
	davem@...emloft.net,
	edumazet@...gle.com,
	kuba@...nel.org,
	linux-kernel@...r.kernel.org,
	linux-ppp@...r.kernel.org,
	netdev@...r.kernel.org,
	pabeni@...hat.com,
	syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot]

Author: contact@...aud-lcm.com

#syz test: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git

diff --git a/drivers/net/ppp/ppp_synctty.c b/drivers/net/ppp/ppp_synctty.c
index 644e99fc3623..520d895acc60 100644
--- a/drivers/net/ppp/ppp_synctty.c
+++ b/drivers/net/ppp/ppp_synctty.c
@@ -506,6 +506,11 @@ ppp_sync_txmunge(struct syncppp *ap, struct sk_buff *skb)
 	unsigned char *data;
 	int islcp;
 
+	/* Ensure we can safely access protocol field and LCP code */
+	if (!skb || !pskb_may_pull(skb, 3)) {
+		kfree_skb(skb);
+		return NULL;
+	}
 	data  = skb->data;
 	proto = get_unaligned_be16(data);