On Wed, Jan 20, 2021 at 2:17 AM Jakub Kicinski <k...@kernel.org> wrote: > > On Mon, 18 Jan 2021 14:59:20 +0900 Kuniyuki Iwashima wrote: > > Receiving ACK with a valid SYN cookie, cookie_v4_check() allocates struct > > request_sock and then can allocate inet_rsk(req)->ireq_opt. After that, > > tcp_v4_syn_recv_sock() allocates struct sock and copies ireq_opt to > > inet_sk(sk)->inet_opt. Normally, tcp_v4_syn_recv_sock() inserts the full > > socket into ehash and sets NULL to ireq_opt. Otherwise, > > tcp_v4_syn_recv_sock() has to reset inet_opt by NULL and free the full > > socket. > > > > The commit 01770a1661657 ("tcp: fix race condition when creating child > > sockets from syncookies") added a new path, in which more than one cores > > create full sockets for the same SYN cookie. Currently, the core which > > loses the race frees the full socket without resetting inet_opt, resulting > > in that both sock_put() and reqsk_put() call kfree() for the same memory: > > > > sock_put > > sk_free > > __sk_free > > sk_destruct > > __sk_destruct > > sk->sk_destruct/inet_sock_destruct > > kfree(rcu_dereference_protected(inet->inet_opt, 1)); > > > > reqsk_put > > reqsk_free > > __reqsk_free > > req->rsk_ops->destructor/tcp_v4_reqsk_destructor > > kfree(rcu_dereference_protected(inet_rsk(req)->ireq_opt, 1)); > > > > Calling kmalloc() between the double kfree() can lead to use-after-free, so > > this patch fixes it by setting NULL to inet_opt before sock_put(). > > > > As a side note, this kind of issue does not happen for IPv6. This is > > because tcp_v6_syn_recv_sock() clones both ipv6_opt and pktopts which > > correspond to ireq_opt in IPv4. > > > > Fixes: 01770a166165 ("tcp: fix race condition when creating child sockets > > from syncookies") > > CC: Ricardo Dias <rd...@singlestore.com> > > Signed-off-by: Kuniyuki Iwashima <kun...@amazon.co.jp> > > Reviewed-by: Benjamin Herrenschmidt <b...@amazon.com> > > Ricardo, Eric, any reason this was written this way?
Well, I guess that was a plain bug. IPv4 options are not used often I think. Reviewed-by: Eric Dumazet <eduma...@google.com>