Merge branch 'kcm-fix-two-syzcaller-issues'

Tom Herbert says:

====================
kcm: fix two syzcaller issues

In this patch set:

- Don't allow attaching non-TCP or listener sockets to a KCM mux.
- In kcm_attach Check if sk_user_data is already set. This is
  under lock to avoid race conditions. More work is need to make
  all of the users of sk_user_data to use the same locking.

- v2
  Remove unncessary check for not PF_KCM in kcm_attach (suggested by
  Guillaume Nault)
====================

Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 21 insertions, 4 deletions

diff --git a/net/kcm/kcmsock.c b/net/kcm/kcmsock.c
index d4e98f20fc2a..4a8d407f8902 100644
--- a/net/kcm/kcmsock.c
+++ b/net/kcm/kcmsock.c
@@ -1387,8 +1387,13 @@ static int kcm_attach(struct socket *sock, struct socket *csock,
         if (!csk)
                 return -EINVAL;
 
-        /* We must prevent loops or risk deadlock ! */
-        if (csk->sk_family == PF_KCM)
+        /* Only allow TCP sockets to be attached for now */
+        if ((csk->sk_family != AF_INET && csk->sk_family != AF_INET6) ||
+            csk->sk_protocol != IPPROTO_TCP)
+                return -EOPNOTSUPP;
+
+        /* Don't allow listeners or closed sockets */
+        if (csk->sk_state == TCP_LISTEN || csk->sk_state == TCP_CLOSE)
                 return -EOPNOTSUPP;
 
         psock = kmem_cache_zalloc(kcm_psockp, GFP_KERNEL);
@@ -1405,9 +1410,18 @@ static int kcm_attach(struct socket *sock, struct socket *csock,
                 return err;
         }
 
-        sock_hold(csk);
-
         write_lock_bh(&csk->sk_callback_lock);
+
+        /* Check if sk_user_data is aready by KCM or someone else.
+         * Must be done under lock to prevent race conditions.
+         */
+        if (csk->sk_user_data) {
+                write_unlock_bh(&csk->sk_callback_lock);
+                strp_done(&psock->strp);
+                kmem_cache_free(kcm_psockp, psock);
+                return -EALREADY;
+        }
+
         psock->save_data_ready = csk->sk_data_ready;
         psock->save_write_space = csk->sk_write_space;
         psock->save_state_change = csk->sk_state_change;
@@ -1415,8 +1429,11 @@ static int kcm_attach(struct socket *sock, struct socket *csock,
         csk->sk_data_ready = psock_data_ready;
         csk->sk_write_space = psock_write_space;
         csk->sk_state_change = psock_state_change;
+
         write_unlock_bh(&csk->sk_callback_lock);
 
+        sock_hold(csk);
+
         /* Finished initialization, now add the psock to the MUX. */
         spin_lock_bh(&mux->lock);
         head = &mux->psocks;