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Date: Fri, 22 Mar 2019 12:14:28 +0100 From: Greg Kroah-Hartman <gregkh@...uxfoundation.org> To: linux-kernel@...r.kernel.org Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>, stable@...r.kernel.org, Xiumei Mu <xmu@...hat.com>, Xin Long <lucien.xin@...il.com>, "David S. Miller" <davem@...emloft.net> Subject: [PATCH 4.4 130/230] pptp: dst_release sk_dst_cache in pptp_sock_destruct 4.4-stable review patch. If anyone has any objections, please let me know. ------------------ From: Xin Long <lucien.xin@...il.com> [ Upstream commit 9417d81f4f8adfe20a12dd1fadf73a618cbd945d ] 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: 00959ade36ac ("PPTP: PPP over IPv4 (Point-to-Point Tunneling Protocol)") Reported-by: Xiumei Mu <xmu@...hat.com> Signed-off-by: Xin Long <lucien.xin@...il.com> Signed-off-by: David S. Miller <davem@...emloft.net> Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org> --- drivers/net/ppp/pptp.c | 1 + 1 file changed, 1 insertion(+) --- a/drivers/net/ppp/pptp.c +++ b/drivers/net/ppp/pptp.c @@ -577,6 +577,7 @@ static void pptp_sock_destruct(struct so 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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