Commit de9c4861 authored by Eric Dumazet's avatar Eric Dumazet Committed by Jakub Kicinski
Browse files

pptp: ensure minimal skb length in pptp_xmit() 



Commit aabc6596 ("net: ppp: Add bound checking for skb data
on ppp_sync_txmung") fixed ppp_sync_txmunge()

We need a similar fix in pptp_xmit(), otherwise we might
read uninit data as reported by syzbot.

BUG: KMSAN: uninit-value in pptp_xmit+0xc34/0x2720 drivers/net/ppp/pptp.c:193
  pptp_xmit+0xc34/0x2720 drivers/net/ppp/pptp.c:193
  ppp_channel_bridge_input drivers/net/ppp/ppp_generic.c:2290 [inline]
  ppp_input+0x1d6/0xe60 drivers/net/ppp/ppp_generic.c:2314
  pppoe_rcv_core+0x1e8/0x760 drivers/net/ppp/pppoe.c:379
  sk_backlog_rcv+0x142/0x420 include/net/sock.h:1148
  __release_sock+0x1d3/0x330 net/core/sock.c:3213
  release_sock+0x6b/0x270 net/core/sock.c:3767
  pppoe_sendmsg+0x15d/0xcb0 drivers/net/ppp/pppoe.c:904
  sock_sendmsg_nosec net/socket.c:712 [inline]
  __sock_sendmsg+0x330/0x3d0 net/socket.c:727
  ____sys_sendmsg+0x893/0xd80 net/socket.c:2566
  ___sys_sendmsg+0x271/0x3b0 net/socket.c:2620
  __sys_sendmmsg+0x2d9/0x7c0 net/socket.c:2709

Fixes: 1da177e4 ("Linux-2.6.12-rc2")
Reported-by: default avatar <syzbot+afad90ffc8645324afe5@syzkaller.appspotmail.com>
Closes: https://lore.kernel.org/netdev/68887d86.a00a0220.b12ec.00cd.GAE@google.com/T/#u


Signed-off-by: default avatarEric Dumazet <edumazet@google.com>
Reviewed-by: default avatarDawid Osuchowski <dawid.osuchowski@linux.intel.com>
Link: https://patch.msgid.link/20250729080207.1863408-1-edumazet@google.com


Signed-off-by: default avatarJakub Kicinski <kuba@kernel.org>
parent 3b98c935

drivers/net/ppp/pptp.c

+9 −6
Original line number Diff line number Diff line
@@ -159,9 +159,7 @@ static int pptp_xmit(struct ppp_channel *chan, struct sk_buff *skb) 
	int len;

	unsigned char *data;

	__u32 seq_recv;





	struct rtable *rt;

	struct rtable *rt = NULL;

	struct net_device *tdev;

	struct iphdr  *iph;

	int    max_headroom;
@@ -179,16 +177,20 @@ static int pptp_xmit(struct ppp_channel *chan, struct sk_buff *skb) 


	if (skb_headroom(skb) < max_headroom || skb_cloned(skb) || skb_shared(skb)) {

		struct sk_buff *new_skb = skb_realloc_headroom(skb, max_headroom);

		if (!new_skb) {

			ip_rt_put(rt);



		if (!new_skb)

			goto tx_error;

		}



		if (skb->sk)

			skb_set_owner_w(new_skb, skb->sk);

		consume_skb(skb);

		skb = new_skb;

	}



	/* Ensure we can safely access protocol field and LCP code */

	if (!pskb_may_pull(skb, 3))

		goto tx_error;



	data = skb->data;

	islcp = ((data[0] << 8) + data[1]) == PPP_LCP && 1 <= data[2] && data[2] <= 7;
@@ -262,6 +264,7 @@ static int pptp_xmit(struct ppp_channel *chan, struct sk_buff *skb) 
	return 1;



tx_error:

	ip_rt_put(rt);

	kfree_skb(skb);

	return 1;

}