CVE-2025-68227

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

mptcp: Fix proto fallback detection with BPF

The sockmap feature allows bpf syscall from userspace, or based on bpf sockops, replacing the sk_prot of sockets during protocol stack processing with sockmaps custom read/write interfaces.

tcp_rcv_state_process() syn_recv_sock()/subflow_syn_recv_sock() tcp_init_transfer(BPF_SOCK_OPS_PASSIVE_ESTABLISHED_CB) bpf_skops_established <== sockops bpf_sock_map_update(sk) <== call bpf helper tcp_bpf_update_proto() <== update sk_prot

When the server has MPTCP enabled but the client sends a TCP SYN without MPTCP, subflow_syn_recv_sock() performs a fallback on the subflow, replacing the subflow sks sk_prot with the native sk_prot.

subflow_syn_recv_sock() subflow_ulp_fallback() subflow_drop_ctx() mptcp_subflow_ops_undo_override()

Then, this subflow can be normally used by sockmap, which replaces the native sk_prot with sockmaps custom sk_prot. The issue occurs when the user executes accept::mptcp_stream_accept::mptcp_fallback_tcp_ops(). Here, it uses sk->sk_prot to compare with the native sk_prot, but this is incorrect when sockmap is used, as we may incorrectly set sk->sk_socket->ops.

This fix uses the more generic sk_family for the comparison instead.

Additionally, this also prevents a WARNING from occurring:

result from ./scripts/decode_stacktrace.sh: ————[ cut here ]———— WARNING: CPU: 0 PID: 337 at net/mptcp/protocol.c:68 mptcp_stream_accept (net/mptcp/protocol.c:4005) Modules linked in: …

PKRU: 55555554 Call Trace: do_accept (net/socket.c:1989) __sys_accept4 (net/socket.c:2028 net/socket.c:2057) __x64_sys_accept (net/socket.c:2067) x64_sys_call (arch/x86/entry/syscall_64.c:41) do_syscall_64 (arch/x86/entry/syscall_64.c:63 arch/x86/entry/syscall_64.c:94) entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:130) RIP: 0033:0x7f87ac92b83d

—[ end trace 0000000000000000 ]—

Affected Software

References

• https://git.kernel.org/stable/c/037cc50589643342d69185b663ecf9d26cce91e8
• https://git.kernel.org/stable/c/1a0d5c74af9b6ba9ffdf1172de5a1a6df5922a00
• https://git.kernel.org/stable/c/344974ea1a3ca30e4920687b0091bda4438cebdb
• https://git.kernel.org/stable/c/7ee8f015eb47907745e2070184a8ab1e442ac3c4
• https://git.kernel.org/stable/c/92c4092fe012ecdfa5fb05d394f1c1d8f91ad81c
• https://git.kernel.org/stable/c/9b1980b6f23fa30bf12add19f37c7458625099eb
• https://git.kernel.org/stable/c/c77b3b79a92e3345aa1ee296180d1af4e7031f8f