CVE-2024-35894

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

mptcp: prevent BPF accessing lowat from a subflow socket.

Alexei reported the following splat:

WARNING: CPU: 32 PID: 3276 at net/mptcp/subflow.c:1430 subflow_data_ready+0x147/0x1c0

Modules linked in: dummy bpf_testmod(O) [last unloaded: bpf_test_no_cfi(O)]

CPU: 32 PID: 3276 Comm: test_progs Tainted: GO 6.8.0-12873-g2c43c33bfd23

Call Trace:

<TASK>

mptcp_set_rcvlowat+0x79/0x1d0

sk_setsockopt+0x6c0/0x1540

__bpf_setsockopt+0x6f/0x90

bpf_sock_ops_setsockopt+0x3c/0x90

bpf_prog_509ce5db2c7f9981_bpf_test_sockopt_int+0xb4/0x11b

bpf_prog_dce07e362d941d2b_bpf_test_socket_sockopt+0x12b/0x132

bpf_prog_348c9b5faaf10092_skops_sockopt+0x954/0xe86

__cgroup_bpf_run_filter_sock_ops+0xbc/0x250

tcp_connect+0x879/0x1160

tcp_v6_connect+0x50c/0x870

mptcp_connect+0x129/0x280

__inet_stream_connect+0xce/0x370

inet_stream_connect+0x36/0x50

bpf_trampoline_6442491565+0x49/0xef

inet_stream_connect+0x5/0x50

__sys_connect+0x63/0x90

__x64_sys_connect+0x14/0x20

The root cause of the issue is that bpf allows accessing mptcp-level

proto_ops from a tcp subflow scope.

Fix the issue detecting the problematic call and preventing any action.