load seccomp_export_bpf generated code into the kernel

Question

http://man7.org/linux/man-pages/man3/seccomp_export_bpf.3.html how can I load the generated code into kernel? Which are possible use cases for this function?

Answer 1

How can I load the generated code into kernel?

If you're using seccomp_export_bpf(const scmp_filter_ctx ctx, int fd), then you already have an initialized scmp_filter_ctx object, ctx, in which case, you can simply do:

int rc = seccomp_load(ctx);

No need to use seccomp_export_bpf to load the filter in the kernel.

Which are possible use cases for this function?

I'm guessing seccomp_export_bpf is mostly useful when you want to keep a copy of your filter on disk for future use. For example, you could do (from the man page example):

filter_fd = open("/tmp/seccomp_filter.bpf", O_WRONLY);
if (filter_fd == -1) {
     rc = -errno;
     goto out;
}

rc = seccomp_export_bpf(ctx, filter_fd);

To then load that exported filter in the kernel you could do:

char filter[4096];
int length = read(0, filter, 4096);
if (length < 0) {
    goto out;
}
struct sock_fprog bpf_prog = {
    .len = length / sizeof(struct sock_filter),
    .filter = filter,
};
rc = prctl(PR_SET_SECCOMP, SECCOMP_MODE_FILTER, &bpf_prog);