path: root/net/unix/diag.c
diff options
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 /net/unix/diag.c
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>
Diffstat (limited to 'net/unix/diag.c')
1 files changed, 2 insertions, 1 deletions
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;