[PATCH] mptcp: Fix deadlock in mptcp_sendmsg()

Shigeru Yoshida
2023-01-05T20:13:31Z

__mptcp_close_ssk() can be called from mptcp_sendmsg() with subflow
socket locked. This can cause a deadlock as below:

mptcp_sendmsg()
mptcp_sendmsg_fastopen() --> lock ssk
tcp_sendmsg_fastopen()
__inet_stream_connect()
mptcp_disconnect()
mptcp_destroy_common()
__mptcp_close_ssk() --> lock ssk again

This patch fixes the issue by skipping locking for subflow socket
which is already locked.

Fixes: d98a82a6afc7 ("mptcp: handle defer connect in mptcp_sendmsg")
Signed-off-by: Shigeru Yoshida <syoshida@redhat.com>
---
net/mptcp/protocol.c | 15 +++++++++------
net/mptcp/protocol.h | 4 ++--
2 files changed, 11 insertions(+), 8 deletions(-)

diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
index f6f93957275b..979265f66082 100644
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -1672,9 +1672,9 @@ static int mptcp_sendmsg_fastopen(struct sock *sk, struct sock *ssk, struct msgh
lock_sock(ssk);
msg->msg_flags |= MSG_DONTWAIT;
msk->connect_flags = O_NONBLOCK;
- msk->is_sendmsg = 1;
+ msk->sendmsg_locked_sk = ssk;
ret = tcp_sendmsg_fastopen(ssk, msg, copied_syn, len, NULL);
- msk->is_sendmsg = 0;
+ msk->sendmsg_locked_sk = NULL;
msg->msg_flags = saved_flags;
release_sock(ssk);

@@ -2319,7 +2319,8 @@ static void __mptcp_close_ssk(struct sock *sk, struct sock *ssk,
if (dispose_it)
list_del(&subflow->node);

- lock_sock_nested(ssk, SINGLE_DEPTH_NESTING);
+ if (msk->sendmsg_locked_sk != ssk)
+ lock_sock_nested(ssk, SINGLE_DEPTH_NESTING);

if (flags & MPTCP_CF_FASTCLOSE) {
/* be sure to force the tcp_disconnect() path,
@@ -2335,7 +2336,8 @@ static void __mptcp_close_ssk(struct sock *sk, struct sock *ssk,
tcp_disconnect(ssk, 0);
msk->subflow->state = SS_UNCONNECTED;
mptcp_subflow_ctx_reset(subflow);
- release_sock(ssk);
+ if (msk->sendmsg_locked_sk != ssk)
+ release_sock(ssk);

goto out;
}
@@ -2362,7 +2364,8 @@ static void __mptcp_close_ssk(struct sock *sk, struct sock *ssk,
/* close acquired an extra ref */
__sock_put(ssk);
}
- release_sock(ssk);
+ if (msk->sendmsg_locked_sk != ssk)
+ release_sock(ssk);

sock_put(ssk);

@@ -3532,7 +3535,7 @@ static int mptcp_connect(struct sock *sk, struct sockaddr *uaddr, int addr_len)
/* if reaching here via the fastopen/sendmsg path, the caller already
* acquired the subflow socket lock, too.
*/
- if (msk->is_sendmsg)
+ if (msk->sendmsg_locked_sk)
err = __inet_stream_connect(ssock, uaddr, addr_len, msk->connect_flags, 1);
else
err = inet_stream_connect(ssock, uaddr, addr_len, msk->connect_flags);
diff --git a/net/mptcp/protocol.h b/net/mptcp/protocol.h
index 955fb3d88eb3..43afc399e16b 100644
--- a/net/mptcp/protocol.h
+++ b/net/mptcp/protocol.h
@@ -294,8 +294,7 @@ struct mptcp_sock {
u8 mpc_endpoint_id;
u8 recvmsg_inq:1,
cork:1,
- nodelay:1,
- is_sendmsg:1;
+ nodelay:1;
int connect_flags;
struct work_struct work;
struct sk_buff *ooo_last_skb;
@@ -318,6 +317,7 @@ struct mptcp_sock {
u32 setsockopt_seq;
char ca_name[TCP_CA_NAME_MAX];
struct mptcp_sock *dl_next;
+ struct sock *sendmsg_locked_sk;
};

#define mptcp_data_lock(sk) spin_lock_bh(&(sk)->sk_lock.slock)
--
2.39.0