On Tue, May 3, 2022 at 6:27 AM David Laight <David.Laight@xxxxxxxxxx> wrote: > > From: Paolo Abeni > > Sent: 03 May 2022 10:03 > > > > 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? > > Wouldn't a more generic solution be to add a flag to sock_create_kern() > so that it acquires a reference to the namespace? > This could be a bit on one of the existing parameters - like SOCK_NONBLOCK. > > I've a driver that uses __sock_create() in order to get that reference. > I'm pretty sure the extra 'security' check will never fail. > This would be silly really. Definition of a 'kernel socket' is that it does not hold a reference to the namespace. (otherwise a netns could not be destroyed by user space) A kernel layer using kernel sockets needs to properly dismantle them when a namespace is destroyed. In the RDS case, the socket was a user socket, or RDS lacked proper tracking of all the sockets so that they can be dismantled properly.
