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 [1] Reported-by: syzbot <syzbot+694120e1002c117747ed@xxxxxxxxxxxxxxxxxxxxxxxxx> Fixes: 26abe14379f8e2fa ("net: Modify sk_alloc to not reference count the netns of kernel sockets.") Fixes: 8a68173691f03661 ("net: sk_clone_lock() should only do get_net() if the parent is not a kernel socket") Signed-off-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx> Tested-by: syzbot <syzbot+694120e1002c117747ed@xxxxxxxxxxxxxxxxxxxxxxxxx> --- Changes in v2: Add Fixes: tag. Move to inside lock_sock() section. I chose 26abe14379f8e2fa and 8a68173691f03661 which went to 4.2 for Fixes: tag, for refcount was implicitly taken when 70041088e3b97662 ("RDS: Add TCP transport to RDS") was added to 2.6.32. net/rds/tcp.c | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/net/rds/tcp.c b/net/rds/tcp.c index 5327d130c4b5..2f638f8b7b1e 100644 --- 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; -- 2.34.1
