CVE-2025-23145

In the Linux kernel, the following vulnerability has been resolved:

mptcp: fix NULL pointer in can_accept_new_subflow

When testing valkey benchmark tool with MPTCP, the kernel panics in

'mptcp_can_accept_new_subflow' because subflow_req->msk is NULL.

Call trace:

mptcp_can_accept_new_subflow (./net/mptcp/subflow.c:63 (discriminator 4)) (P)

subflow_syn_recv_sock (./net/mptcp/subflow.c:854)

tcp_check_req (./net/ipv4/tcp_minisocks.c:863)

tcp_v4_rcv (./net/ipv4/tcp_ipv4.c:2268)

ip_protocol_deliver_rcu (./net/ipv4/ip_input.c:207)

ip_local_deliver_finish (./net/ipv4/ip_input.c:234)

ip_local_deliver (./net/ipv4/ip_input.c:254)

ip_rcv_finish (./net/ipv4/ip_input.c:449)

...

According to the debug log, the same req received two SYN-ACK in a very

short time, very likely because the client retransmits the syn ack due

to multiple reasons.

Even if the packets are transmitted with a relevant time interval, they

can be processed by the server on different CPUs concurrently). The

'subflow_req->msk' ownership is transferred to the subflow the first,

and there will be a risk of a null pointer dereference here.

This patch fixes this issue by moving the 'subflow_req->msk' under the

`own_req == true` conditional.

Note that the !msk check in subflow_hmac_valid() can be dropped, because

the same check already exists under the own_req mpj branch where the

code has been moved to.