From: Gang Yan <yangang@kylinos.cn>

The "update_socket_protocol" interface is designed to empower user space
with the capability to customize and modify socket protocols leveraging
BPF methods. Currently, it has only granted the fmod_ret permission,
allowing for modifications to return values. We are extending the
permissions further by 'ALLOW_ERROR_INJECTION', thereby facilitating
the development of user-space programs with enhanced flexibility and
convenience.

When we attempt to modify the return value of "update_socket_protocol"
to "IPPROTO_MPTCP" using the below code based on the BCC tool:

'''
int kprobe__update_socket_protocol(void* ctx)
{
    ...
    bpf_override_return(ctx, IPPROTO_MPTCP);
    ...
}
'''

But an error occurs:

'''
ioctl(PERF_EVENT_IOC_SET_BPF): Invalid argument
Traceback (most recent call last):
  File "/media/yangang/work/Code/BCC/test.py", line 27, in <module>
    b = BPF(text=prog)
        ^^^^^^^^^^^^^^
  File "/usr/lib/python3/dist-packages/bcc/__init__.py", line 487, \
                  in __init__ self._trace_autoload()
  File "/usr/lib/python3/dist-packages/bcc/__init__.py", line 1466, \
                  in _trace_autoload self.attach_kprobe(
  File "/usr/lib/python3/dist-packages/bcc/__init__.py", line 855,\
                  in attach_kprobe
    raise Exception("Failed to attach BPF program %s to kprobe %s"
Exception: Failed to attach BPF program b'kprobe__update_socket_protocol' \
  to kprobe b'update_socket_protocol', it's not traceable \
  (either non-existing, inlined, or marked as "notrace")
'''

This patch can fix the issue.

Suggested-by: Geliang Tang <geliang@kernel.org>
Signed-off-by: Gang Yan <yangang@kylinos.cn>
---
 net/socket.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/net/socket.c b/net/socket.c
index fcbdd5bc47ac..63ce1caf75eb 100644
--- a/net/socket.c
+++ b/net/socket.c
@@ -1695,6 +1695,7 @@ __weak noinline int update_socket_protocol(int family, int type, int protocol)
 {
 	return protocol;
 }
+ALLOW_ERROR_INJECTION(update_socket_protocol, ERRNO);
 
 __bpf_hook_end();
 
-- 
2.43.0

Hi Gang,

Thank you for your modifications, that's great!

Our CI did some validations and here is its report:

- KVM Validation: normal: Unstable: 1 failed test(s): mptcp_connect_mmap 🔴
- KVM Validation: debug: Success! ✅
- KVM Validation: btf (only bpftest_all): Success! ✅
- Task: https://github.com/multipath-tcp/mptcp_net-next/actions/runs/10502583505

Initiator: Patchew Applier
Commits: https://github.com/multipath-tcp/mptcp_net-next/commits/889545cfdd86
Patchwork: https://patchwork.kernel.org/project/mptcp/list/?series=881988


If there are some issues, you can reproduce them using the same environment as
the one used by the CI thanks to a docker image, e.g.:

    $ cd [kernel source code]
    $ docker run -v "${PWD}:${PWD}:rw" -w "${PWD}" --privileged --rm -it \
        --pull always mptcp/mptcp-upstream-virtme-docker:latest \
        auto-normal

For more details:

    https://github.com/multipath-tcp/mptcp-upstream-virtme-docker


Please note that despite all the efforts that have been already done to have a
stable tests suite when executed on a public CI like here, it is possible some
reported issues are not due to your modifications. Still, do not hesitate to
help us improve that ;-)

Cheers,
MPTCP GH Action bot
Bot operated by Matthieu Baerts (NGI0 Core)