4.20-stable review patch. If anyone has any objections, please let me know.
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From: Al Viro viro@zeniv.linux.org.uk
[ Upstream commit ae3b564179bfd06f32d051b9e5d72ce4b2a07c37 ]
Several u->addr and u->path users are not holding any locks in common with unix_bind(). unix_state_lock() is useless for those purposes.
u->addr is assign-once and *(u->addr) is fully set up by the time we set u->addr (all under unix_table_lock). u->path is also set in the same critical area, also before setting u->addr, and any unix_sock with ->path filled will have non-NULL ->addr.
So setting ->addr with smp_store_release() is all we need for those "lockless" users - just have them fetch ->addr with smp_load_acquire() and don't even bother looking at ->path if they see NULL ->addr.
Users of ->addr and ->path fall into several classes now: 1) ones that do smp_load_acquire(u->addr) and access *(u->addr) and u->path only if smp_load_acquire() has returned non-NULL. 2) places holding unix_table_lock. These are guaranteed that *(u->addr) is seen fully initialized. If unix_sock is in one of the "bound" chains, so's ->path. 3) unix_sock_destructor() using ->addr is safe. All places that set u->addr are guaranteed to have seen all stores *(u->addr) while holding a reference to u and unix_sock_destructor() is called when (atomic) refcount hits zero. 4) unix_release_sock() using ->path is safe. unix_bind() is serialized wrt unix_release() (normally - by struct file refcount), and for the instances that had ->path set by unix_bind() unix_release_sock() comes from unix_release(), so they are fine. Instances that had it set in unix_stream_connect() either end up attached to a socket (in unix_accept()), in which case the call chain to unix_release_sock() and serialization are the same as in the previous case, or they never get accept'ed and unix_release_sock() is called when the listener is shut down and its queue gets purged. In that case the listener's queue lock provides the barriers needed - unix_stream_connect() shoves our unix_sock into listener's queue under that lock right after having set ->path and eventual unix_release_sock() caller picks them from that queue under the same lock right before calling unix_release_sock(). 5) unix_find_other() use of ->path is pointless, but safe - it happens with successful lookup by (abstract) name, so ->path.dentry is guaranteed to be NULL there.
earlier-variant-reviewed-by: "Paul E. McKenney" paulmck@linux.ibm.com Signed-off-by: Al Viro viro@zeniv.linux.org.uk Signed-off-by: David S. Miller davem@davemloft.net Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- net/unix/af_unix.c | 57 +++++++++++++++++++++++++++++---------------------- net/unix/diag.c | 3 +- security/lsm_audit.c | 10 +++++--- 3 files changed, 41 insertions(+), 29 deletions(-)
--- a/net/unix/af_unix.c +++ b/net/unix/af_unix.c @@ -890,7 +890,7 @@ retry: addr->hash ^= sk->sk_type;
__unix_remove_socket(sk); - u->addr = addr; + smp_store_release(&u->addr, addr); __unix_insert_socket(&unix_socket_table[addr->hash], sk); spin_unlock(&unix_table_lock); err = 0; @@ -1060,7 +1060,7 @@ static int unix_bind(struct socket *sock
err = 0; __unix_remove_socket(sk); - u->addr = addr; + smp_store_release(&u->addr, addr); __unix_insert_socket(list, sk);
out_unlock: @@ -1331,15 +1331,29 @@ restart: RCU_INIT_POINTER(newsk->sk_wq, &newu->peer_wq); otheru = unix_sk(other);
- /* copy address information from listening to new sock*/ - if (otheru->addr) { - refcount_inc(&otheru->addr->refcnt); - newu->addr = otheru->addr; - } + /* copy address information from listening to new sock + * + * The contents of *(otheru->addr) and otheru->path + * are seen fully set up here, since we have found + * otheru in hash under unix_table_lock. Insertion + * into the hash chain we'd found it in had been done + * in an earlier critical area protected by unix_table_lock, + * the same one where we'd set *(otheru->addr) contents, + * as well as otheru->path and otheru->addr itself. + * + * Using smp_store_release() here to set newu->addr + * is enough to make those stores, as well as stores + * to newu->path visible to anyone who gets newu->addr + * by smp_load_acquire(). IOW, the same warranties + * as for unix_sock instances bound in unix_bind() or + * in unix_autobind(). + */ if (otheru->path.dentry) { path_get(&otheru->path); newu->path = otheru->path; } + refcount_inc(&otheru->addr->refcnt); + smp_store_release(&newu->addr, otheru->addr);
/* Set credentials */ copy_peercred(sk, other); @@ -1453,7 +1467,7 @@ out: static int unix_getname(struct socket *sock, struct sockaddr *uaddr, int peer) { struct sock *sk = sock->sk; - struct unix_sock *u; + struct unix_address *addr; DECLARE_SOCKADDR(struct sockaddr_un *, sunaddr, uaddr); int err = 0;
@@ -1468,19 +1482,15 @@ static int unix_getname(struct socket *s sock_hold(sk); }
- u = unix_sk(sk); - unix_state_lock(sk); - if (!u->addr) { + addr = smp_load_acquire(&unix_sk(sk)->addr); + if (!addr) { sunaddr->sun_family = AF_UNIX; sunaddr->sun_path[0] = 0; err = sizeof(short); } else { - struct unix_address *addr = u->addr; - err = addr->len; memcpy(sunaddr, addr->name, addr->len); } - unix_state_unlock(sk); sock_put(sk); out: return err; @@ -2073,11 +2083,11 @@ static int unix_seqpacket_recvmsg(struct
static void unix_copy_addr(struct msghdr *msg, struct sock *sk) { - struct unix_sock *u = unix_sk(sk); + struct unix_address *addr = smp_load_acquire(&unix_sk(sk)->addr);
- if (u->addr) { - msg->msg_namelen = u->addr->len; - memcpy(msg->msg_name, u->addr->name, u->addr->len); + if (addr) { + msg->msg_namelen = addr->len; + memcpy(msg->msg_name, addr->name, addr->len); } }
@@ -2581,15 +2591,14 @@ static int unix_open_file(struct sock *s if (!ns_capable(sock_net(sk)->user_ns, CAP_NET_ADMIN)) return -EPERM;
- unix_state_lock(sk); + if (!smp_load_acquire(&unix_sk(sk)->addr)) + return -ENOENT; + path = unix_sk(sk)->path; - if (!path.dentry) { - unix_state_unlock(sk); + if (!path.dentry) return -ENOENT; - }
path_get(&path); - unix_state_unlock(sk);
fd = get_unused_fd_flags(O_CLOEXEC); if (fd < 0) @@ -2830,7 +2839,7 @@ static int unix_seq_show(struct seq_file (s->sk_state == TCP_ESTABLISHED ? SS_CONNECTING : SS_DISCONNECTING), sock_i_ino(s));
- if (u->addr) { + if (u->addr) { // under unix_table_lock here int i, len; seq_putc(seq, ' ');
--- a/net/unix/diag.c +++ b/net/unix/diag.c @@ -10,7 +10,8 @@
static int sk_diag_dump_name(struct sock *sk, struct sk_buff *nlskb) { - struct unix_address *addr = unix_sk(sk)->addr; + /* might or might not have unix_table_lock */ + struct unix_address *addr = smp_load_acquire(&unix_sk(sk)->addr);
if (!addr) return 0; --- a/security/lsm_audit.c +++ b/security/lsm_audit.c @@ -321,6 +321,7 @@ static void dump_common_audit_data(struc if (a->u.net->sk) { struct sock *sk = a->u.net->sk; struct unix_sock *u; + struct unix_address *addr; int len = 0; char *p = NULL;
@@ -351,14 +352,15 @@ static void dump_common_audit_data(struc #endif case AF_UNIX: u = unix_sk(sk); + addr = smp_load_acquire(&u->addr); + if (!addr) + break; if (u->path.dentry) { audit_log_d_path(ab, " path=", &u->path); break; } - if (!u->addr) - break; - len = u->addr->len-sizeof(short); - p = &u->addr->name->sun_path[0]; + len = addr->len-sizeof(short); + p = &addr->name->sun_path[0]; audit_log_format(ab, " path="); if (*p) audit_log_untrustedstring(ab, p);