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authorKuniyuki Iwashima <kuniyu@amazon.co.jp>2021-01-18 14:59:20 +0900
committerJakub Kicinski <kuba@kernel.org>2021-01-20 08:56:16 -0800
commitc89dffc70b340780e5b933832d8c3e045ef3791e (patch)
treea2be5f1b8798e1c177172a7d4e6e5f7531c43843 /net
parentb3741b43880bfb7319424edd600da47d1cd8c680 (diff)
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 <rdias@singlestore.com> Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.co.jp> Reviewed-by: Benjamin Herrenschmidt <benh@amazon.com> Reviewed-by: Eric Dumazet <edumazet@google.com> Link: https://lore.kernel.org/r/20210118055920.82516-1-kuniyu@amazon.co.jp Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Diffstat (limited to 'net')
-rw-r--r--net/ipv4/tcp_ipv4.c4
1 files changed, 2 insertions, 2 deletions
diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index 4e82745d336f..777306b5bc22 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;