+static int apply_seccomp(uint32_t *syscall_filter) {
+ static const struct sock_filter header[] = {
+ VALIDATE_ARCHITECTURE,
+ EXAMINE_SYSCALL
+ };
+ static const struct sock_filter footer[] = {
+ _KILL_PROCESS
+ };
+
+ int i;
+ unsigned n;
+ struct sock_filter *f;
+ struct sock_fprog prog;
+
+ assert(syscall_filter);
+
+ /* First: count the syscalls to check for */
+ for (i = 0, n = 0; i < syscall_max(); i++)
+ if (syscall_filter[i >> 4] & (1 << (i & 31)))
+ n++;
+
+ /* Second: build the filter program from a header the syscall
+ * matches and the footer */
+ f = alloca(sizeof(struct sock_filter) * (ELEMENTSOF(header) + 2*n + ELEMENTSOF(footer)));
+ memcpy(f, header, sizeof(header));
+
+ for (i = 0, n = 0; i < syscall_max(); i++)
+ if (syscall_filter[i >> 4] & (1 << (i & 31))) {
+ struct sock_filter item[] = {
+ BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, i, 0, 1),
+ BPF_STMT(BPF_RET+BPF_K, SECCOMP_RET_ALLOW)
+ };
+
+ assert_cc(ELEMENTSOF(item) == 2);
+
+ f[ELEMENTSOF(header) + 2*n] = item[0];
+ f[ELEMENTSOF(header) + 2*n+1] = item[1];
+
+ n++;
+ }
+
+ memcpy(f + (ELEMENTSOF(header) + 2*n), footer, sizeof(footer));
+
+ /* Third: install the filter */
+ zero(prog);
+ prog.len = ELEMENTSOF(header) + ELEMENTSOF(footer) + 2*n;
+ prog.filter = f;
+ if (prctl(PR_SET_SECCOMP, SECCOMP_MODE_FILTER, &prog) < 0)
+ return -errno;
+
+ return 0;
+}
+