net: rds: acquire refcount on TCP sockets

syzbot is reporting use-after-free read in tcp_retransmit_timer() [1],
for TCP socket used by RDS is accessing sock_net() without acquiring a
refcount on net namespace. Since TCP's retransmission can happen after
a process which created net namespace terminated, we need to explicitly
acquire a refcount.

Link: https://syzkaller.appspot.com/bug?extid=694120e1002c117747ed
Reported-by: syzbot <syzbot+694120e1002c117747ed@syzkaller.appspotmail.com>
Fixes: 645b84d8bec9d544 ("net: Modify sk_alloc to not reference count the netns of kernel sockets.")
Fixes: f1ab38c355cf5745 ("net: sk_clone_lock() should only do get_net() if the parent is not a kernel socket")
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Tested-by: syzbot <syzbot+694120e1002c117747ed@syzkaller.appspotmail.com>
Link: https://lore.kernel.org/r/a5fb1fc4-2284-3359-f6a0-e4e390239d7b@I-love.SAKURA.ne.jp
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

diff --git a/net/rds/tcp.c b/net/rds/tcp.c
index 5327d130c4b5691e788bbbcb990a349d714ad8d4..2f638f8b7b1e7e0a4b12ccccbe2c52013c3ea972 100644 (file)
--- a/net/rds/tcp.c
+++ b/net/rds/tcp.c
@@ -495,6 +495,14 @@ void rds_tcp_tune(struct socket *sock)
 
        tcp_sock_set_nodelay(sock->sk);
        lock_sock(sk);
+       /* TCP timer functions might access net namespace even after
+        * a process which created this net namespace terminated.
+        */
+       if (!sk->sk_net_refcnt) {
+               sk->sk_net_refcnt = 1;
+               get_net_track(net, &sk->ns_tracker, GFP_KERNEL);
+               sock_inuse_add(net, 1);
+       }
        if (rtn->sndbuf_size > 0) {
                sk->sk_sndbuf = rtn->sndbuf_size;
                sk->sk_userlocks |= SOCK_SNDBUF_LOCK;