SO_PEERSEC protections in sk_getsockopt()?

[Paul Moore]

Hi Martin,

In commit 4ff09db1b79b ("bpf: net: Change sk_getsockopt() to take the
sockptr_t argument") I see you wrapped the getsockopt value/len
pointers with sockptr_t and in the SO_PEERSEC case you pass the
sockptr_t:user field to avoid having to update the LSM hook and
implementations.  I think that's fine, especially as you note that
eBPF does not support fetching the SO_PEERSEC information, but I think
it would be good to harden this case to prevent someone from calling
sk_getsockopt(SO_PEERSEC) with kernel pointers.  What do you think of
something like this?

  static int sk_getsockopt(...)
  {
    /* ... */
    case SO_PEERSEC:
      if (optval.is_kernel || optlen.is_kernel)
        return -EINVAL;
      return security_socket_getpeersec_stream(...);
    /* ... */
  }

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