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mptcp: fix use-after-free on tcp fallback
When an mptcp socket connects to a tcp peer or when a middlebox interferes with tcp options, mptcp needs to fall back to plain tcp. Problem is that mptcp is trying to be too clever in this case: It attempts to close the mptcp meta sk and transparently replace it with the (only) subflow tcp sk. Unfortunately, this is racy -- the socket is already exposed to userspace. Any parallel calls to send/recv/setsockopt etc. can cause use-after-free: BUG: KASAN: use-after-free in atomic_try_cmpxchg include/asm-generic/atomic-instrumented.h:693 [inline] CPU: 1 PID: 2083 Comm: syz-executor.1 Not tainted 5.5.0 #2 atomic_try_cmpxchg include/asm-generic/atomic-instrumented.h:693 [inline] queued_spin_lock include/asm-generic/qspinlock.h:78 [inline] do_raw_spin_lock include/linux/spinlock.h:181 [inline] __raw_spin_lock_bh include/linux/spinlock_api_smp.h:136 [inline] _raw_spin_lock_bh+0x71/0xd0 kernel/locking/spinlock.c:175 spin_lock_bh include/linux/spinlock.h:343 [inline] __lock_sock+0x105/0x190 net/core/sock.c:2414 lock_sock_nested+0x10f/0x140 net/core/sock.c:2938 lock_sock include/net/sock.h:1516 [inline] mptcp_setsockopt+0x2f/0x1f0 net/mptcp/protocol.c:800 __sys_setsockopt+0x152/0x240 net/socket.c:2130 __do_sys_setsockopt net/socket.c:2146 [inline] __se_sys_setsockopt net/socket.c:2143 [inline] __x64_sys_setsockopt+0xba/0x150 net/socket.c:2143 do_syscall_64+0xb7/0x3d0 arch/x86/entry/common.c:294 entry_SYSCALL_64_after_hwframe+0x44/0xa9 While the use-after-free can be resolved, there is another problem: sock->ops and sock->sk assignments are not atomic, i.e. we may get calls into mptcp functions with sock->sk already pointing at the subflow socket, or calls into tcp functions with a mptcp meta sk. Remove the fallback code and call the relevant functions for the (only) subflow in case the mptcp socket is connected to tcp peer. Reported-by: Christoph Paasch <cpaasch@apple.com> Diagnosed-by: Paolo Abeni <pabeni@redhat.com> Signed-off-by: Florian Westphal <fw@strlen.de> Reviewed-by: Mat Martineau <mathew.j.martineau@linux.intel.com> Tested-by: Christoph Paasch <cpaasch@apple.com> Signed-off-by: David S. Miller <davem@davemloft.net>
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2c22c06ce4
1 changed files with 6 additions and 70 deletions
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@ -24,58 +24,6 @@
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#define MPTCP_SAME_STATE TCP_MAX_STATES
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static void __mptcp_close(struct sock *sk, long timeout);
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static const struct proto_ops *tcp_proto_ops(struct sock *sk)
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{
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#if IS_ENABLED(CONFIG_MPTCP_IPV6)
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if (sk->sk_family == AF_INET6)
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return &inet6_stream_ops;
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#endif
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return &inet_stream_ops;
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}
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/* MP_CAPABLE handshake failed, convert msk to plain tcp, replacing
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* socket->sk and stream ops and destroying msk
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* return the msk socket, as we can't access msk anymore after this function
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* completes
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* Called with msk lock held, releases such lock before returning
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*/
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static struct socket *__mptcp_fallback_to_tcp(struct mptcp_sock *msk,
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struct sock *ssk)
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{
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struct mptcp_subflow_context *subflow;
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struct socket *sock;
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struct sock *sk;
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sk = (struct sock *)msk;
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sock = sk->sk_socket;
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subflow = mptcp_subflow_ctx(ssk);
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/* detach the msk socket */
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list_del_init(&subflow->node);
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sock_orphan(sk);
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sock->sk = NULL;
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/* socket is now TCP */
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lock_sock(ssk);
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sock_graft(ssk, sock);
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if (subflow->conn) {
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/* We can't release the ULP data on a live socket,
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* restore the tcp callback
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*/
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mptcp_subflow_tcp_fallback(ssk, subflow);
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sock_put(subflow->conn);
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subflow->conn = NULL;
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}
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release_sock(ssk);
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sock->ops = tcp_proto_ops(ssk);
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/* destroy the left-over msk sock */
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__mptcp_close(sk, 0);
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return sock;
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}
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/* If msk has an initial subflow socket, and the MP_CAPABLE handshake has not
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* completed yet or has failed, return the subflow socket.
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* Otherwise return NULL.
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@ -93,10 +41,6 @@ static bool __mptcp_needs_tcp_fallback(const struct mptcp_sock *msk)
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return msk->first && !sk_is_mptcp(msk->first);
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}
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/* if the mp_capable handshake has failed, it fallbacks msk to plain TCP,
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* releases the socket lock and returns a reference to the now TCP socket.
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* Otherwise returns NULL
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*/
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static struct socket *__mptcp_tcp_fallback(struct mptcp_sock *msk)
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{
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sock_owned_by_me((const struct sock *)msk);
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@ -105,15 +49,11 @@ static struct socket *__mptcp_tcp_fallback(struct mptcp_sock *msk)
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return NULL;
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if (msk->subflow) {
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/* the first subflow is an active connection, discart the
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* paired socket
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*/
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msk->subflow->sk = NULL;
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sock_release(msk->subflow);
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msk->subflow = NULL;
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release_sock((struct sock *)msk);
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return msk->subflow;
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}
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return __mptcp_fallback_to_tcp(msk, msk->first);
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return NULL;
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}
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static bool __mptcp_can_create_subflow(const struct mptcp_sock *msk)
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@ -640,12 +580,14 @@ static void mptcp_subflow_shutdown(struct sock *ssk, int how)
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}
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/* Called with msk lock held, releases such lock before returning */
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static void __mptcp_close(struct sock *sk, long timeout)
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static void mptcp_close(struct sock *sk, long timeout)
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{
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struct mptcp_subflow_context *subflow, *tmp;
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struct mptcp_sock *msk = mptcp_sk(sk);
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LIST_HEAD(conn_list);
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lock_sock(sk);
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mptcp_token_destroy(msk->token);
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inet_sk_state_store(sk, TCP_CLOSE);
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@ -662,12 +604,6 @@ static void __mptcp_close(struct sock *sk, long timeout)
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sk_common_release(sk);
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}
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static void mptcp_close(struct sock *sk, long timeout)
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{
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lock_sock(sk);
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__mptcp_close(sk, timeout);
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}
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static void mptcp_copy_inaddrs(struct sock *msk, const struct sock *ssk)
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{
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#if IS_ENABLED(CONFIG_MPTCP_IPV6)
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