From 278a3de5abc7901805689a66340b5af9882b4f9a Mon Sep 17 00:00:00 2001 From: "David S. Miller" Date: Thu, 31 May 2007 15:19:20 -0700 Subject: [PATCH] [AF_UNIX]: Fix datagram connect race causing an OOPS. Based upon an excellent bug report and initial patch by Frederik Deweerdt. The UNIX datagram connect code blindly dereferences other->sk_socket via the call down to the security_unix_may_send() function. Without locking 'other' that pointer can go NULL via unix_release_sock() which does sock_orphan() which also marks the socket SOCK_DEAD. So we have to lock both 'sk' and 'other' yet avoid all kinds of potential deadlocks (connect to self is OK for datagram sockets and it is possible for two datagram sockets to perform a simultaneous connect to each other). So what we do is have a "double lock" function similar to how we handle this situation in other areas of the kernel. We take the lock of the socket pointer with the smallest address first in order to avoid ABBA style deadlocks. Once we have them both locked, we check to see if SOCK_DEAD is set for 'other' and if so, drop everything and retry the lookup. Signed-off-by: David S. Miller --- net/unix/af_unix.c | 43 ++++++++++++++++++++++++++++++++++++++----- 1 file changed, 38 insertions(+), 5 deletions(-) diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c index 453ede86a65b..87c794d8fa2d 100644 --- a/net/unix/af_unix.c +++ b/net/unix/af_unix.c @@ -858,6 +858,31 @@ out_mknod_parent: goto out_up; } +static void unix_state_double_lock(struct sock *sk1, struct sock *sk2) +{ + if (unlikely(sk1 == sk2) || !sk2) { + unix_state_lock(sk1); + return; + } + if (sk1 < sk2) { + unix_state_lock(sk1); + unix_state_lock_nested(sk2); + } else { + unix_state_lock(sk2); + unix_state_lock_nested(sk1); + } +} + +static void unix_state_double_unlock(struct sock *sk1, struct sock *sk2) +{ + if (unlikely(sk1 == sk2) || !sk2) { + unix_state_unlock(sk1); + return; + } + unix_state_unlock(sk1); + unix_state_unlock(sk2); +} + static int unix_dgram_connect(struct socket *sock, struct sockaddr *addr, int alen, int flags) { @@ -877,11 +902,19 @@ static int unix_dgram_connect(struct socket *sock, struct sockaddr *addr, !unix_sk(sk)->addr && (err = unix_autobind(sock)) != 0) goto out; +restart: other=unix_find_other(sunaddr, alen, sock->type, hash, &err); if (!other) goto out; - unix_state_lock(sk); + unix_state_double_lock(sk, other); + + /* Apparently VFS overslept socket death. Retry. */ + if (sock_flag(other, SOCK_DEAD)) { + unix_state_double_unlock(sk, other); + sock_put(other); + goto restart; + } err = -EPERM; if (!unix_may_send(sk, other)) @@ -896,7 +929,7 @@ static int unix_dgram_connect(struct socket *sock, struct sockaddr *addr, * 1003.1g breaking connected state with AF_UNSPEC */ other = NULL; - unix_state_lock(sk); + unix_state_double_lock(sk, other); } /* @@ -905,19 +938,19 @@ static int unix_dgram_connect(struct socket *sock, struct sockaddr *addr, if (unix_peer(sk)) { struct sock *old_peer = unix_peer(sk); unix_peer(sk)=other; - unix_state_unlock(sk); + unix_state_double_unlock(sk, other); if (other != old_peer) unix_dgram_disconnected(sk, old_peer); sock_put(old_peer); } else { unix_peer(sk)=other; - unix_state_unlock(sk); + unix_state_double_unlock(sk, other); } return 0; out_unlock: - unix_state_unlock(sk); + unix_state_double_unlock(sk, other); sock_put(other); out: return err; -- 2.20.1