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authorAl Viro <viro@zeniv.linux.org.uk>2019-02-15 20:09:35 +0000
committerDavid S. Miller <davem@davemloft.net>2019-02-20 20:06:28 -0800
commitae3b564179bfd06f32d051b9e5d72ce4b2a07c37 (patch)
tree97d40baf6c1a1b952800fd5e2ab5b348696d79a3
parenta8fef9ba58c9966ddb1fec916d8d8137c9d8bc89 (diff)
missing barriers in some of unix_sock ->addr and ->path accesses
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>
-rw-r--r--net/unix/af_unix.c57
-rw-r--r--net/unix/diag.c3
-rw-r--r--security/lsm_audit.c10
3 files changed, 41 insertions, 29 deletions
diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
index 74d1eed7cbd4..a95d479caeea 100644
--- 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, struct sockaddr *uaddr, int addr_len)
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 *sock, struct sockaddr *uaddr, int peer)
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 socket *sock, struct msghdr *msg,
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 *sk)
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 *seq, void *v)
(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, ' ');
diff --git a/net/unix/diag.c b/net/unix/diag.c
index 384c84e83462..3183d9b8ab33 100644
--- 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;
diff --git a/security/lsm_audit.c b/security/lsm_audit.c
index f84001019356..33028c098ef3 100644
--- a/security/lsm_audit.c
+++ b/security/lsm_audit.c
@@ -321,6 +321,7 @@ static void dump_common_audit_data(struct audit_buffer *ab,
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(struct audit_buffer *ab,
#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);