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authorFlorian Westphal <fw@strlen.de>2020-02-04 18:12:30 +0100
committerDavid S. Miller <davem@davemloft.net>2020-02-05 14:08:03 +0100
commit2c22c06ce426a0d025a3dacd17cd8868f3dbe96b (patch)
treee544155827704116a15fe1533c82c23403813d86 /net
parent8b7a07c7d4420c7d684f661697c6a878040c8b65 (diff)
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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>
Diffstat (limited to 'net')
-rw-r--r--net/mptcp/protocol.c76
1 files changed, 6 insertions, 70 deletions
diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
index 3bccee455688..353f2d16b986 100644
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -24,58 +24,6 @@
#define MPTCP_SAME_STATE TCP_MAX_STATES
-static void __mptcp_close(struct sock *sk, long timeout);
-
-static const struct proto_ops *tcp_proto_ops(struct sock *sk)
-{
-#if IS_ENABLED(CONFIG_MPTCP_IPV6)
- if (sk->sk_family == AF_INET6)
- return &inet6_stream_ops;
-#endif
- return &inet_stream_ops;
-}
-
-/* MP_CAPABLE handshake failed, convert msk to plain tcp, replacing
- * socket->sk and stream ops and destroying msk
- * return the msk socket, as we can't access msk anymore after this function
- * completes
- * Called with msk lock held, releases such lock before returning
- */
-static struct socket *__mptcp_fallback_to_tcp(struct mptcp_sock *msk,
- struct sock *ssk)
-{
- struct mptcp_subflow_context *subflow;
- struct socket *sock;
- struct sock *sk;
-
- sk = (struct sock *)msk;
- sock = sk->sk_socket;
- subflow = mptcp_subflow_ctx(ssk);
-
- /* detach the msk socket */
- list_del_init(&subflow->node);
- sock_orphan(sk);
- sock->sk = NULL;
-
- /* socket is now TCP */
- lock_sock(ssk);
- sock_graft(ssk, sock);
- if (subflow->conn) {
- /* We can't release the ULP data on a live socket,
- * restore the tcp callback
- */
- mptcp_subflow_tcp_fallback(ssk, subflow);
- sock_put(subflow->conn);
- subflow->conn = NULL;
- }
- release_sock(ssk);
- sock->ops = tcp_proto_ops(ssk);
-
- /* destroy the left-over msk sock */
- __mptcp_close(sk, 0);
- return sock;
-}
-
/* If msk has an initial subflow socket, and the MP_CAPABLE handshake has not
* completed yet or has failed, return the subflow socket.
* Otherwise return NULL.
@@ -93,10 +41,6 @@ static bool __mptcp_needs_tcp_fallback(const struct mptcp_sock *msk)
return msk->first && !sk_is_mptcp(msk->first);
}
-/* if the mp_capable handshake has failed, it fallbacks msk to plain TCP,
- * releases the socket lock and returns a reference to the now TCP socket.
- * Otherwise returns NULL
- */
static struct socket *__mptcp_tcp_fallback(struct mptcp_sock *msk)
{
sock_owned_by_me((const struct sock *)msk);
@@ -105,15 +49,11 @@ static struct socket *__mptcp_tcp_fallback(struct mptcp_sock *msk)
return NULL;
if (msk->subflow) {
- /* the first subflow is an active connection, discart the
- * paired socket
- */
- msk->subflow->sk = NULL;
- sock_release(msk->subflow);
- msk->subflow = NULL;
+ release_sock((struct sock *)msk);
+ return msk->subflow;
}
- return __mptcp_fallback_to_tcp(msk, msk->first);
+ return NULL;
}
static bool __mptcp_can_create_subflow(const struct mptcp_sock *msk)
@@ -640,12 +580,14 @@ static void mptcp_subflow_shutdown(struct sock *ssk, int how)
}
/* Called with msk lock held, releases such lock before returning */
-static void __mptcp_close(struct sock *sk, long timeout)
+static void mptcp_close(struct sock *sk, long timeout)
{
struct mptcp_subflow_context *subflow, *tmp;
struct mptcp_sock *msk = mptcp_sk(sk);
LIST_HEAD(conn_list);
+ lock_sock(sk);
+
mptcp_token_destroy(msk->token);
inet_sk_state_store(sk, TCP_CLOSE);
@@ -662,12 +604,6 @@ static void __mptcp_close(struct sock *sk, long timeout)
sk_common_release(sk);
}
-static void mptcp_close(struct sock *sk, long timeout)
-{
- lock_sock(sk);
- __mptcp_close(sk, timeout);
-}
-
static void mptcp_copy_inaddrs(struct sock *msk, const struct sock *ssk)
{
#if IS_ENABLED(CONFIG_MPTCP_IPV6)