syzbot reported a recursive lock warning in rds_tcp_get_peer_sport() as it calls inet6_getname() which acquires the socket lock that was already held by __release_sock(). kworker/u8:6/2985 is trying to acquire lock: ffff88807a07aa20 (k-sk_lock-AF_INET6){+.+.}-{0:0}, at: lock_sock include/net/sock.h:1709 [inline] ffff88807a07aa20 (k-sk_lock-AF_INET6){+.+.}-{0:0}, at: inet6_getname+0x15d/0x650 net/ipv6/af_inet6.c:533 but task is already holding lock: ffff88807a07aa20 (k-sk_lock-AF_INET6){+.+.}-{0:0}, at: lock_sock include/net/sock.h:1709 [inline] ffff88807a07aa20 (k-sk_lock-AF_INET6){+.+.}-{0:0}, at: tcp_sock_set_cork+0x2c/0x2e0 net/ipv4/tcp.c:3694 lock_sock_nested+0x48/0x100 net/core/sock.c:3780 lock_sock include/net/sock.h:1709 [inline] inet6_getname+0x15d/0x650 net/ipv6/af_inet6.c:533 rds_tcp_get_peer_sport net/rds/tcp_listen.c:70 [inline] rds_tcp_conn_slots_available+0x288/0x470 net/rds/tcp_listen.c:149 rds_recv_hs_exthdrs+0x60f/0x7c0 net/rds/recv.c:265 rds_recv_incoming+0x9f6/0x12d0 net/rds/recv.c:389 rds_tcp_data_recv+0x7f1/0xa40 net/rds/tcp_recv.c:243 __tcp_read_sock+0x196/0x970 net/ipv4/tcp.c:1702 rds_tcp_read_sock net/rds/tcp_recv.c:277 [inline] rds_tcp_data_ready+0x369/0x950 net/rds/tcp_recv.c:331 tcp_rcv_established+0x19e9/0x2670 net/ipv4/tcp_input.c:6675 tcp_v6_do_rcv+0x8eb/0x1ba0 net/ipv6/tcp_ipv6.c:1609 sk_backlog_rcv include/net/sock.h:1185 [inline] __release_sock+0x1b8/0x3a0 net/core/sock.c:3213 Reading from the socket struct directly is safe from possible paths. For rds_tcp_accept_one(), the socket has just been accepted and is not yet exposed to concurrent access. For rds_tcp_conn_slots_available(), direct access avoids the recursive deadlock seen during backlog processing where the socket lock is already held from the __release_sock(). However, rds_tcp_conn_slots_available() is also called from the normal softirq path via tcp_data_ready() where the lock is not held. This is also safe because inet_dport is a stable 16 bits field. A READ_ONCE() annotation as the value might be accessed lockless in a concurrent access context. Note that it is also safe to call rds_tcp_conn_slots_available() from rds_conn_shutdown() because the fan-out is disabled. Fixes: 9d27a0fb122f ("net/rds: Trigger rds_send_ping() more than once") Reported-by: syzbot+5efae91f60932839f0a5@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=5efae91f60932839f0a5 Signed-off-by: Fernando Fernandez Mancera --- v2: clarified commit message and add a comment around rds_conn_shutdown() path v3: used READ_ONCE() for lockless read and adjusted commit message --- net/rds/connection.c | 3 +++ net/rds/tcp_listen.c | 28 +++++----------------------- 2 files changed, 8 insertions(+), 23 deletions(-) diff --git a/net/rds/connection.c b/net/rds/connection.c index 185f73b01694..a542f94c0214 100644 --- a/net/rds/connection.c +++ b/net/rds/connection.c @@ -455,6 +455,9 @@ void rds_conn_shutdown(struct rds_conn_path *cp) rcu_read_unlock(); } + /* we do not hold the socket lock here but it is safe because + * fan-out is disabled when calling conn_slots_available() + */ if (conn->c_trans->conn_slots_available) conn->c_trans->conn_slots_available(conn, false); } diff --git a/net/rds/tcp_listen.c b/net/rds/tcp_listen.c index 6fb5c928b8fd..dce7ac9d3197 100644 --- a/net/rds/tcp_listen.c +++ b/net/rds/tcp_listen.c @@ -59,30 +59,12 @@ void rds_tcp_keepalive(struct socket *sock) static int rds_tcp_get_peer_sport(struct socket *sock) { - union { - struct sockaddr_storage storage; - struct sockaddr addr; - struct sockaddr_in sin; - struct sockaddr_in6 sin6; - } saddr; - int sport; - - if (kernel_getpeername(sock, &saddr.addr) >= 0) { - switch (saddr.addr.sa_family) { - case AF_INET: - sport = ntohs(saddr.sin.sin_port); - break; - case AF_INET6: - sport = ntohs(saddr.sin6.sin6_port); - break; - default: - sport = -1; - } - } else { - sport = -1; - } + struct sock *sk = sock->sk; + + if (!sk) + return -1; - return sport; + return ntohs(READ_ONCE(inet_sk(sk)->inet_dport)); } /* rds_tcp_accept_one_path(): if accepting on cp_index > 0, make sure the -- 2.53.0