l2tp: Restore socket refcount when sendmsg succeeds

The sendmsg() syscall handler for PPPoL2TP doesn't decrease the socket
reference counter after successful transmissions. Any successful
sendmsg() call from userspace will then increase the reference counter
forever, thus preventing the kernel's session and tunnel data from
being freed later on.

The problem only happens when writing directly on L2TP sockets.
PPP sockets attached to L2TP are unaffected as the PPP subsystem
uses pppol2tp_xmit() which symmetrically increase/decrease reference
counters.

This patch adds the missing call to sock_put() before returning from
pppol2tp_sendmsg().

Signed-off-by: Guillaume Nault <g.nault@alphalink.fr>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/l2tp/l2tp_ppp.c b/net/l2tp/l2tp_ppp.c
index 3f4e3afc191a524d57c29659324ddc0ac6cd9c1e..6a53371dba1f1b357f9cd4f34b7af166ed324eab 100644 (file)
--- a/net/l2tp/l2tp_ppp.c
+++ b/net/l2tp/l2tp_ppp.c
@@ -355,6 +355,7 @@ static int pppol2tp_sendmsg(struct kiocb *iocb, struct socket *sock, struct msgh
        l2tp_xmit_skb(session, skb, session->hdr_len);
 
        sock_put(ps->tunnel_sock);
+       sock_put(sk);
 
        return error;