sctp: fix ASCONF list handling

->auto_asconf_splist is per namespace and mangled by functions like
sctp_setsockopt_auto_asconf() which doesn't guarantee any serialization.

Also, the call to inet_sk_copy_descendant() was backuping
->auto_asconf_list through the copy but was not honoring
->do_auto_asconf, which could lead to list corruption if it was
different between both sockets.

This commit thus fixes the list handling by using ->addr_wq_lock
spinlock to protect the list. A special handling is done upon socket
creation and destruction for that. Error handlig on sctp_init_sock()
will never return an error after having initialized asconf, so
sctp_destroy_sock() can be called without addrq_wq_lock. The lock now
will be take on sctp_close_sock(), before locking the socket, so we
don't do it in inverse order compared to sctp_addr_wq_timeout_handler().

Instead of taking the lock on sctp_sock_migrate() for copying and
restoring the list values, it's preferred to avoid rewritting it by
implementing sctp_copy_descendant().

Issue was found with a test application that kept flipping sysctl
default_auto_asconf on and off, but one could trigger it by issuing
simultaneous setsockopt() calls on multiple sockets or by
creating/destroying sockets fast enough. This is only triggerable
locally.

Fixes: 9f7d653b67ae ("sctp: Add Auto-ASCONF support (core).")
Reported-by: Ji Jianwen <jiji@redhat.com>
Suggested-by: Neil Horman <nhorman@tuxdriver.com>
Suggested-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
Acked-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

3 files changed, 37 insertions, 11 deletions

diff --git a/include/net/netns/sctp.h b/include/net/netns/sctp.h
index 3573a81815ad..8ba379f9e467 100644
--- a/include/net/netns/sctp.h
+++ b/include/net/netns/sctp.h
@@ -31,6 +31,7 @@ struct netns_sctp {
         struct list_head addr_waitq;
         struct timer_list addr_wq_timer;
         struct list_head auto_asconf_splist;
+        /* Lock that protects both addr_waitq and auto_asconf_splist */
         spinlock_t addr_wq_lock;
 
         /* Lock that protects the local_addr_list writers */
diff --git a/include/net/sctp/structs.h b/include/net/sctp/structs.h
index 2bb2fcf5b11f..495c87e367b3 100644
--- a/include/net/sctp/structs.h
+++ b/include/net/sctp/structs.h
@@ -223,6 +223,10 @@ struct sctp_sock {
         atomic_t pd_mode;
         /* Receive to here while partial delivery is in effect. */
         struct sk_buff_head pd_lobby;
+
+        /* These must be the last fields, as they will skipped on copies,
+         * like on accept and peeloff operations
+         */
         struct list_head auto_asconf_list;
         int do_auto_asconf;
 };
diff --git a/net/sctp/socket.c b/net/sctp/socket.c
index f09de7fac2e6..5f6c4e61325b 100644
--- a/net/sctp/socket.c
+++ b/net/sctp/socket.c
@@ -1528,8 +1528,10 @@ static void sctp_close(struct sock *sk, long timeout)
 
         /* Supposedly, no process has access to the socket, but
          * the net layers still may.
+         * Also, sctp_destroy_sock() needs to be called with addr_wq_lock
+         * held and that should be grabbed before socket lock.
          */
-        local_bh_disable();
+        spin_lock_bh(&net->sctp.addr_wq_lock);
         bh_lock_sock(sk);
 
         /* Hold the sock, since sk_common_release() will put sock_put()
@@ -1539,7 +1541,7 @@ static void sctp_close(struct sock *sk, long timeout)
         sk_common_release(sk);
 
         bh_unlock_sock(sk);
-        local_bh_enable();
+        spin_unlock_bh(&net->sctp.addr_wq_lock);
 
         sock_put(sk);
 
@@ -3580,6 +3582,7 @@ static int sctp_setsockopt_auto_asconf(struct sock *sk, char __user *optval,
         if ((val && sp->do_auto_asconf) || (!val && !sp->do_auto_asconf))
                 return 0;
 
+        spin_lock_bh(&sock_net(sk)->sctp.addr_wq_lock);
         if (val == 0 && sp->do_auto_asconf) {
                 list_del(&sp->auto_asconf_list);
                 sp->do_auto_asconf = 0;
@@ -3588,6 +3591,7 @@ static int sctp_setsockopt_auto_asconf(struct sock *sk, char __user *optval,
                     &sock_net(sk)->sctp.auto_asconf_splist);
                 sp->do_auto_asconf = 1;
         }
+        spin_unlock_bh(&sock_net(sk)->sctp.addr_wq_lock);
         return 0;
 }
 
@@ -4121,18 +4125,28 @@ static int sctp_init_sock(struct sock *sk)
         local_bh_disable();
         percpu_counter_inc(&sctp_sockets_allocated);
         sock_prot_inuse_add(net, sk->sk_prot, 1);
+
+        /* Nothing can fail after this block, otherwise
+         * sctp_destroy_sock() will be called without addr_wq_lock held
+         */
         if (net->sctp.default_auto_asconf) {
+                spin_lock(&sock_net(sk)->sctp.addr_wq_lock);
                 list_add_tail(&sp->auto_asconf_list,
                     &net->sctp.auto_asconf_splist);
                 sp->do_auto_asconf = 1;
-        } else
+                spin_unlock(&sock_net(sk)->sctp.addr_wq_lock);
+        } else {
                 sp->do_auto_asconf = 0;
+        }
+
         local_bh_enable();
 
         return 0;
 }
 
-/* Cleanup any SCTP per socket resources.  */
+/* Cleanup any SCTP per socket resources. Must be called with
+ * sock_net(sk)->sctp.addr_wq_lock held if sp->do_auto_asconf is true
+ */
 static void sctp_destroy_sock(struct sock *sk)
 {
         struct sctp_sock *sp;
@@ -7195,6 +7209,19 @@ void sctp_copy_sock(struct sock *newsk, struct sock *sk,
         newinet->mc_list = NULL;
 }
 
+static inline void sctp_copy_descendant(struct sock *sk_to,
+                                        const struct sock *sk_from)
+{
+        int ancestor_size = sizeof(struct inet_sock) +
+                            sizeof(struct sctp_sock) -
+                            offsetof(struct sctp_sock, auto_asconf_list);
+
+        if (sk_from->sk_family == PF_INET6)
+                ancestor_size += sizeof(struct ipv6_pinfo);
+
+        __inet_sk_copy_descendant(sk_to, sk_from, ancestor_size);
+}
+
 /* Populate the fields of the newsk from the oldsk and migrate the assoc
  * and its messages to the newsk.
  */
@@ -7209,7 +7236,6 @@ static void sctp_sock_migrate(struct sock *oldsk, struct sock *newsk,
         struct sk_buff *skb, *tmp;
         struct sctp_ulpevent *event;
         struct sctp_bind_hashbucket *head;
-        struct list_head tmplist;
 
         /* Migrate socket buffer sizes and all the socket level options to the
          * new socket.
@@ -7217,12 +7243,7 @@ static void sctp_sock_migrate(struct sock *oldsk, struct sock *newsk,
         newsk->sk_sndbuf = oldsk->sk_sndbuf;
         newsk->sk_rcvbuf = oldsk->sk_rcvbuf;
         /* Brute force copy old sctp opt. */
-        if (oldsp->do_auto_asconf) {
-                memcpy(&tmplist, &newsp->auto_asconf_list, sizeof(tmplist));
-                inet_sk_copy_descendant(newsk, oldsk);
-                memcpy(&newsp->auto_asconf_list, &tmplist, sizeof(tmplist));
-        } else
-                inet_sk_copy_descendant(newsk, oldsk);
+        sctp_copy_descendant(newsk, oldsk);
 
         /* Restore the ep value that was overwritten with the above structure
          * copy.