l2tp: Restore socket refcount when sendmsg succeeds

[ Upstream commit 8b82547e33e85fc24d4d172a93c796de1fefa81a ]

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/net/l2tp/l2tp_ppp.c b/net/l2tp/l2tp_ppp.c
index 1addd9f3f40a05938273ce0a99c6d5d9c5d940bb..9728a7564a703e207714f2c64aca2b70954f8b2e 100644 (file)
--- a/net/l2tp/l2tp_ppp.c
+++ b/net/l2tp/l2tp_ppp.c
@@ -360,6 +360,7 @@ 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;