kcm: lock lower socket in kcm_attach

Need to lock lower socket in order to provide mutual exclusion
with kcm_unattach.

v2: Add Reported-by for syzbot

Fixes: ab7ac4eb9832e32a09f4e804 ("kcm: Kernel Connection Multiplexor module")
Reported-by: syzbot+ea75c0ffcd353d32515f064aaebefc5279e6161e@syzkaller.appspotmail.com
Signed-off-by: Tom Herbert <tom@quantonium.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 23 insertions, 10 deletions

diff --git a/net/kcm/kcmsock.c b/net/kcm/kcmsock.c
index f297d53a11aa..34355fd19f27 100644
--- a/net/kcm/kcmsock.c
+++ b/net/kcm/kcmsock.c
@@ -1381,24 +1381,32 @@ static int kcm_attach(struct socket *sock, struct socket *csock,
                 .parse_msg = kcm_parse_func_strparser,
                 .read_sock_done = kcm_read_sock_done,
         };
-        int err;
+        int err = 0;
 
         csk = csock->sk;
         if (!csk)
                 return -EINVAL;
 
+        lock_sock(csk);
+
         /* 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;
+            csk->sk_protocol != IPPROTO_TCP) {
+                err = -EOPNOTSUPP;
+                goto out;
+        }
 
         /* Don't allow listeners or closed sockets */
-        if (csk->sk_state == TCP_LISTEN || csk->sk_state == TCP_CLOSE)
-                return -EOPNOTSUPP;
+        if (csk->sk_state == TCP_LISTEN || csk->sk_state == TCP_CLOSE) {
+                err = -EOPNOTSUPP;
+                goto out;
+        }
 
         psock = kmem_cache_zalloc(kcm_psockp, GFP_KERNEL);
-        if (!psock)
-                return -ENOMEM;
+        if (!psock) {
+                err = -ENOMEM;
+                goto out;
+        }
 
         psock->mux = mux;
         psock->sk = csk;
@@ -1407,7 +1415,7 @@ static int kcm_attach(struct socket *sock, struct socket *csock,
         err = strp_init(&psock->strp, csk, &cb);
         if (err) {
                 kmem_cache_free(kcm_psockp, psock);
-                return err;
+                goto out;
         }
 
         write_lock_bh(&csk->sk_callback_lock);
@@ -1419,7 +1427,8 @@ static int kcm_attach(struct socket *sock, struct socket *csock,
                 write_unlock_bh(&csk->sk_callback_lock);
                 strp_done(&psock->strp);
                 kmem_cache_free(kcm_psockp, psock);
-                return -EALREADY;
+                err = -EALREADY;
+                goto out;
         }
 
         psock->save_data_ready = csk->sk_data_ready;
@@ -1455,7 +1464,10 @@ static int kcm_attach(struct socket *sock, struct socket *csock,
         /* Schedule RX work in case there are already bytes queued */
         strp_check_rcv(&psock->strp);
 
-        return 0;
+out:
+        release_sock(csk);
+
+        return err;
 }
 
 static int kcm_attach_ioctl(struct socket *sock, struct kcm_attach *info)
@@ -1507,6 +1519,7 @@ static void kcm_unattach(struct kcm_psock *psock)
 
         if (WARN_ON(psock->rx_kcm)) {
                 write_unlock_bh(&csk->sk_callback_lock);
+                release_sock(csk);
                 return;
         }