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 01770a16 ("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: 01770a16 ("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>
parent
b3741b43
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