Hello, On Mon, 2022-05-02 at 10:40 +0900, Tetsuo Handa wrote: > 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; This looks equivalent to the fix presented here: https://lore.kernel.org/all/CANn89i+484ffqb93aQm1N-tjxxvb3WDKX0EbD7318RwRgsatjw@xxxxxxxxxxxxxx/ but the latter looks a more generic solution. @Tetsuo could you please test the above in your setup? Thanks! Paolo
