Commit 0b4f33de authored by Florian Westphal's avatar Florian Westphal Committed by David S. Miller
Browse files

mptcp: fix tcp fallback crash 



Christoph Paasch reports following crash:

general protection fault [..]
CPU: 0 PID: 2874 Comm: syz-executor072 Not tainted 5.6.0-rc5 #62
RIP: 0010:__pv_queued_spin_lock_slowpath kernel/locking/qspinlock.c:471
[..]
 queued_spin_lock_slowpath arch/x86/include/asm/qspinlock.h:50 [inline]
 do_raw_spin_lock include/linux/spinlock.h:181 [inline]
 spin_lock_bh include/linux/spinlock.h:343 [inline]
 __mptcp_flush_join_list+0x44/0xb0 net/mptcp/protocol.c:278
 mptcp_shutdown+0xb3/0x230 net/mptcp/protocol.c:1882
[..]

Problem is that mptcp_shutdown() socket isn't an mptcp socket,
its a plain tcp_sk.  Thus, trying to access mptcp_sk specific
members accesses garbage.

Root cause is that accept() returns a fallback (tcp) socket, not an mptcp
one.  There is code in getpeername to detect this and override the sockets
stream_ops.  But this will only run when accept() caller provided a
sockaddr struct.  "accept(fd, NULL, 0)" will therefore result in
mptcp stream ops, but with sock->sk pointing at a tcp_sk.

Update the existing fallback handling to detect this as well.

Moreover, mptcp_shutdown did not have fallback handling, and
mptcp_poll did it too late so add that there as well.

Reported-by: default avatarChristoph Paasch <cpaasch@apple.com>
Tested-by: default avatarChristoph Paasch <cpaasch@apple.com>
Reviewed-by: default avatarMat Martineau <mathew.j.martineau@linux.intel.com>
Signed-off-by: default avatarMatthieu Baerts <matthieu.baerts@tessares.net>
Signed-off-by: default avatarFlorian Westphal <fw@strlen.de>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent d16fa759

net/mptcp/protocol.c

+46 −4
Original line number Diff line number Diff line
@@ -57,10 +57,43 @@ static bool __mptcp_needs_tcp_fallback(const struct mptcp_sock *msk) 
	return msk->first && !sk_is_mptcp(msk->first);

}



static struct socket *mptcp_is_tcpsk(struct sock *sk)

{

	struct socket *sock = sk->sk_socket;



	if (sock->sk != sk)

		return NULL;



	if (unlikely(sk->sk_prot == &tcp_prot)) {

		/* we are being invoked after mptcp_accept() has

		 * accepted a non-mp-capable flow: sk is a tcp_sk,

		 * not an mptcp one.

		 *

		 * Hand the socket over to tcp so all further socket ops

		 * bypass mptcp.

		 */

		sock->ops = &inet_stream_ops;

		return sock;

#if IS_ENABLED(CONFIG_MPTCP_IPV6)

	} else if (unlikely(sk->sk_prot == &tcpv6_prot)) {

		sock->ops = &inet6_stream_ops;

		return sock;

#endif

	}



	return NULL;

}



static struct socket *__mptcp_tcp_fallback(struct mptcp_sock *msk)

{

	struct socket *sock;



	sock_owned_by_me((const struct sock *)msk);



	sock = mptcp_is_tcpsk((struct sock *)msk);

	if (unlikely(sock))

		return sock;



	if (likely(!__mptcp_needs_tcp_fallback(msk)))

		return NULL;
@@ -84,6 +117,10 @@ static struct socket *__mptcp_socket_create(struct mptcp_sock *msk, int state) 
	struct socket *ssock;

	int err;



	ssock = __mptcp_tcp_fallback(msk);

	if (unlikely(ssock))

		return ssock;



	ssock = __mptcp_nmpc_socket(msk);

	if (ssock)

		goto set_state;
@@ -1752,6 +1789,8 @@ static __poll_t mptcp_poll(struct file *file, struct socket *sock, 


	msk = mptcp_sk(sk);

	lock_sock(sk);

	ssock = __mptcp_tcp_fallback(msk);

	if (!ssock)

		ssock = __mptcp_nmpc_socket(msk);

	if (ssock) {

		mask = ssock->ops->poll(file, ssock, wait);
@@ -1762,9 +1801,6 @@ static __poll_t mptcp_poll(struct file *file, struct socket *sock, 
	release_sock(sk);

	sock_poll_wait(file, sock, wait);

	lock_sock(sk);

	ssock = __mptcp_tcp_fallback(msk);

	if (unlikely(ssock))

		return ssock->ops->poll(file, ssock, NULL);



	if (test_bit(MPTCP_DATA_READY, &msk->flags))

		mask = EPOLLIN | EPOLLRDNORM;
@@ -1783,11 +1819,17 @@ static int mptcp_shutdown(struct socket *sock, int how) 
{

	struct mptcp_sock *msk = mptcp_sk(sock->sk);

	struct mptcp_subflow_context *subflow;

	struct socket *ssock;

	int ret = 0;



	pr_debug("sk=%p, how=%d", msk, how);



	lock_sock(sock->sk);

	ssock = __mptcp_tcp_fallback(msk);

	if (ssock) {

		release_sock(sock->sk);

		return inet_shutdown(ssock, how);

	}



	if (how == SHUT_WR || how == SHUT_RDWR)

		inet_sk_state_store(sock->sk, TCP_FIN_WAIT1);

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