Commit 9417d81f authored Mar 13, 2019 by Xin Long Committed by David S. Miller Mar 13, 2019

pptp: dst_release sk_dst_cache in pptp_sock_destruct



sk_setup_caps() is called to set sk->sk_dst_cache in pptp_connect,
so we have to dst_release(sk->sk_dst_cache) in pptp_sock_destruct,
otherwise, the dst refcnt will leak.

It can be reproduced by this syz log:

  r1 = socket$pptp(0x18, 0x1, 0x2)
  bind$pptp(r1, &(0x7f0000000100)={0x18, 0x2, {0x0, @local}}, 0x1e)
  connect$pptp(r1, &(0x7f0000000000)={0x18, 0x2, {0x3, @remote}}, 0x1e)

Consecutive dmesg warnings will occur:

  unregister_netdevice: waiting for lo to become free. Usage count = 1

v1->v2:
  - use rcu_dereference_protected() instead of rcu_dereference_check(),
    as suggested by Eric.

Fixes: 00959ade ("PPTP: PPP over IPv4 (Point-to-Point Tunneling Protocol)")
Reported-by: Xiumei Mu <xmu@redhat.com>
Signed-off-by: Xin Long <lucien.xin@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

parent 63b6c974

drivers/net/ppp/pptp.c

+1 −0

Original line number	Diff line number	Diff line
		@@ -532,6 +532,7 @@ static void pptp_sock_destruct(struct sock *sk)
		pppox_unbind_sock(sk);
		}
		skb_queue_purge(&sk->sk_receive_queue);
		dst_release(rcu_dereference_protected(sk->sk_dst_cache, 1));
		}

		static int pptp_create(struct net net, struct socket sock, int kern)

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