From 335759211a327d61244580070d74f55561c35895 Mon Sep 17 00:00:00 2001 From: Kuniyuki Iwashima Date: Tue, 10 Mar 2020 17:05:26 +0900 Subject: tcp: Forbid to bind more than one sockets haveing SO_REUSEADDR and SO_REUSEPORT per EUID. If there is no TCP_LISTEN socket on a ephemeral port, we can bind multiple sockets having SO_REUSEADDR to the same port. Then if all sockets bound to the port have also SO_REUSEPORT enabled and have the same EUID, all of them can be listened. This is not safe. Let's say, an application has root privilege and binds sockets to an ephemeral port with both of SO_REUSEADDR and SO_REUSEPORT. When none of sockets is not listened yet, a malicious user can use sudo, exhaust ephemeral ports, and bind sockets to the same ephemeral port, so he or she can call listen and steal the port. To prevent this issue, we must not bind more than one sockets that have the same EUID and both of SO_REUSEADDR and SO_REUSEPORT. On the other hand, if the sockets have different EUIDs, the issue above does not occur. After sockets with different EUIDs are bound to the same port and one of them is listened, no more socket can be listened. This is because the condition below is evaluated true and listen() for the second socket fails. } else if (!reuseport_ok || !reuseport || !sk2->sk_reuseport || rcu_access_pointer(sk->sk_reuseport_cb) || (sk2->sk_state != TCP_TIME_WAIT && !uid_eq(uid, sock_i_uid(sk2)))) { if (inet_rcv_saddr_equal(sk, sk2, true)) break; } Therefore, on the same port, we cannot do listen() for multiple sockets with different EUIDs and any other listen syscalls fail, so the problem does not happen. In this case, we can still call connect() for other sockets that cannot be listened, so we have to succeed to call bind() in order to fully utilize 4-tuples. Summarizing the above, we should be able to bind only one socket having SO_REUSEADDR and SO_REUSEPORT per EUID. Signed-off-by: Kuniyuki Iwashima Signed-off-by: David S. Miller --- net/ipv4/inet_connection_sock.c | 12 +++++++++--- 1 file changed, 9 insertions(+), 3 deletions(-) (limited to 'net/ipv4/inet_connection_sock.c') diff --git a/net/ipv4/inet_connection_sock.c b/net/ipv4/inet_connection_sock.c index 497366b631f3..3b4f81790e3e 100644 --- a/net/ipv4/inet_connection_sock.c +++ b/net/ipv4/inet_connection_sock.c @@ -131,7 +131,7 @@ static int inet_csk_bind_conflict(const struct sock *sk, { struct sock *sk2; bool reuse = sk->sk_reuse; - bool reuseport = !!sk->sk_reuseport && reuseport_ok; + bool reuseport = !!sk->sk_reuseport; kuid_t uid = sock_i_uid((struct sock *)sk); /* @@ -148,10 +148,16 @@ static int inet_csk_bind_conflict(const struct sock *sk, sk->sk_bound_dev_if == sk2->sk_bound_dev_if)) { if (reuse && sk2->sk_reuse && sk2->sk_state != TCP_LISTEN) { - if (!relax && + if ((!relax || + (!reuseport_ok && + reuseport && sk2->sk_reuseport && + !rcu_access_pointer(sk->sk_reuseport_cb) && + (sk2->sk_state == TCP_TIME_WAIT || + uid_eq(uid, sock_i_uid(sk2))))) && inet_rcv_saddr_equal(sk, sk2, true)) break; - } else if (!reuseport || !sk2->sk_reuseport || + } else if (!reuseport_ok || + !reuseport || !sk2->sk_reuseport || rcu_access_pointer(sk->sk_reuseport_cb) || (sk2->sk_state != TCP_TIME_WAIT && !uid_eq(uid, sock_i_uid(sk2)))) { -- cgit v1.2.3