Re: [PATCH 6.12.y] tcp: clear sock_ops cb flags before force-closing a child socket

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Critical] Calling tcp_clear_sock_ops_cb_flags() unconditionally on non-TCP sockets (like DCCP) causes an out-of-bounds write due to an invalid struct tcp_sock cast.
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commit a1e4666cc30271c086f6d9e64c6ebfaddd6750ca
Author: Sechang Lim <rhkrqnwk98@gmail.com>

tcp: clear sock_ops cb flags before force-closing a child socket

A child socket inherits the listener's bpf_sock_ops_cb_flags via
sk_clone_lock(). If its setup fails in tcp_v4_syn_recv_sock() /
tcp_v6_syn_recv_sock(), the child is freed through put_and_exit, where
inet_csk_prepare_forced_close() drops the socket lock and tcp_done() runs
without it.

Link: https://patch.msgid.link/20260611092923.1895982-1-rhkrqnwk98@gmail.com

> diff --git a/include/net/tcp.h b/include/net/tcp.h
> index 1cc25e0b3bdea..c472c1cdd3b83 100644
> --- a/include/net/tcp.h
> +++ b/include/net/tcp.h
[ ... ]
> @@ -2702,6 +2702,11 @@ static inline int tcp_call_bpf_3arg(struct sock *sk, int op, u32 arg1, u32 arg2,
>  	return tcp_call_bpf(sk, op, 3, args);
>  }
>  
> +static inline void tcp_clear_sock_ops_cb_flags(struct sock *sk)
> +{
> +	tcp_sk(sk)->bpf_sock_ops_cb_flags = 0;

[Severity: Critical]
Does this code perform an unsafe cast and memory write for non-TCP sockets?

This accesses an offset that exceeds the bounds of a dccp_sock when
invoked on DCCP sockets, which writes outside the slab allocation for the
socket structure.

> +}
> +
[ ... ]
> diff --git a/net/ipv4/inet_connection_sock.c b/net/ipv4/inet_connection_sock.c
> index 91dcdb7567ace..e0bd8e76fa781 100644
> --- a/net/ipv4/inet_connection_sock.c
> +++ b/net/ipv4/inet_connection_sock.c
[ ... ]
> @@ -1315,6 +1315,14 @@ void inet_csk_destroy_sock(struct sock *sk)
>  }
>  EXPORT_SYMBOL(inet_csk_destroy_sock);
>  
> +void inet_csk_prepare_for_destroy_sock(struct sock *sk)
> +{
> +	/* The below has to be done to allow calling inet_csk_destroy_sock */
> +	tcp_clear_sock_ops_cb_flags(sk);

[Severity: Critical]
Can calling this unconditionally on non-TCP sockets cause memory regressions?

This generic connection socket destruction path in
inet_csk_prepare_for_destroy_sock() blindly invokes a TCP-specific helper,
passing it sockets (like DCCP) that are incompatible with the TCP socket
structure.

This can be triggered by a remote, unauthenticated attacker sending a
malicious or unroutable DCCP connection request to a listening DCCP port.

The regression is triggered on the failure path of DCCP connection setup,
for example when routing fails:

net/dccp/ipv4.c:dccp_v4_request_recv_sock()
   ...
   put_and_exit:
        ...
        inet_csk_prepare_forced_close(newsk);
            inet_csk_prepare_for_destroy_sock(newsk);
                tcp_clear_sock_ops_cb_flags(newsk); /* out-of-bounds write */

> +	sock_set_flag(sk, SOCK_DEAD);
> +	this_cpu_inc(*sk->sk_prot->orphan_count);
> +}
> +

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260907-cve-2026-74268-v1-1-cacea38d7fb3@bootlin.com?part=1