Messages in this thread | | | Date | Tue, 19 Jan 2021 17:17:45 -0800 | From | Jakub Kicinski <> | Subject | Re: [PATCH net] tcp: Fix potential use-after-free due to double kfree(). |
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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 <rdias@singlestore.com> > Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.co.jp> > Reviewed-by: Benjamin Herrenschmidt <benh@amazon.com>
Ricardo, Eric, any reason this was written this way?
> diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c > index 58207c7769d0..87eb614dab27 100644 > --- a/net/ipv4/tcp_ipv4.c > +++ b/net/ipv4/tcp_ipv4.c > @@ -1595,6 +1595,8 @@ struct sock *tcp_v4_syn_recv_sock(const struct sock *sk, struct sk_buff *skb, > tcp_move_syn(newtp, req); > ireq->ireq_opt = NULL; > } else { > + newinet->inet_opt = NULL; > + > if (!req_unhash && found_dup_sk) { > /* This code path should only be executed in the > * syncookie case only > @@ -1602,8 +1604,6 @@ struct sock *tcp_v4_syn_recv_sock(const struct sock *sk, struct sk_buff *skb, > bh_unlock_sock(newsk); > sock_put(newsk); > newsk = NULL; > - } else { > - newinet->inet_opt = NULL; > } > } > return newsk;
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