From c89dffc70b340780e5b933832d8c3e045ef3791e Mon Sep 17 00:00:00 2001 From: Kuniyuki Iwashima Date: Mon, 18 Jan 2021 14:59:20 +0900 Subject: [PATCH] tcp: Fix potential use-after-free due to double kfree() 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 Signed-off-by: Kuniyuki Iwashima Reviewed-by: Benjamin Herrenschmidt Reviewed-by: Eric Dumazet Link: https://lore.kernel.org/r/20210118055920.82516-1-kuniyu@amazon.co.jp Signed-off-by: Jakub Kicinski --- net/ipv4/tcp_ipv4.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c index 4e82745..777306b 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; -- 2.7.4