Documentation: prctl/seccomp_filter

[~andy/linux] / samples / seccomp / dropper.c

diff --git a/samples/seccomp/dropper.c b/samples/seccomp/dropper.c
new file mode 100644 (file)
index 0000000..c69c347
--- /dev/null
+++ b/samples/seccomp/dropper.c
@@ -0,0 +1,68 @@
+/*
+ * Naive system call dropper built on seccomp_filter.
+ *
+ * Copyright (c) 2012 The Chromium OS Authors <chromium-os-dev@chromium.org>
+ * Author: Will Drewry <wad@chromium.org>
+ *
+ * The code may be used by anyone for any purpose,
+ * and can serve as a starting point for developing
+ * applications using prctl(PR_SET_SECCOMP, 2, ...).
+ *
+ * When run, returns the specified errno for the specified
+ * system call number against the given architecture.
+ *
+ * Run this one as root as PR_SET_NO_NEW_PRIVS is not called.
+ */
+
+#include <errno.h>
+#include <linux/audit.h>
+#include <linux/filter.h>
+#include <linux/seccomp.h>
+#include <linux/unistd.h>
+#include <stdio.h>
+#include <stddef.h>
+#include <stdlib.h>
+#include <sys/prctl.h>
+#include <unistd.h>
+
+static int install_filter(int nr, int arch, int error)
+{
+       struct sock_filter filter[] = {
+               BPF_STMT(BPF_LD+BPF_W+BPF_ABS,
+                        (offsetof(struct seccomp_data, arch))),
+               BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, arch, 0, 3),
+               BPF_STMT(BPF_LD+BPF_W+BPF_ABS,
+                        (offsetof(struct seccomp_data, nr))),
+               BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, nr, 0, 1),
+               BPF_STMT(BPF_RET+BPF_K,
+                        SECCOMP_RET_ERRNO|(error & SECCOMP_RET_DATA)),
+               BPF_STMT(BPF_RET+BPF_K, SECCOMP_RET_ALLOW),
+       };
+       struct sock_fprog prog = {
+               .len = (unsigned short)(sizeof(filter)/sizeof(filter[0])),
+               .filter = filter,
+       };
+       if (prctl(PR_SET_SECCOMP, 2, &prog)) {
+               perror("prctl");
+               return 1;
+       }
+       return 0;
+}
+
+int main(int argc, char **argv)
+{
+       if (argc < 5) {
+               fprintf(stderr, "Usage:\n"
+                       "dropper <syscall_nr> <arch> <errno> <prog> [<args>]\n"
+                       "Hint:  AUDIT_ARCH_I386: 0x%X\n"
+                       "       AUDIT_ARCH_X86_64: 0x%X\n"
+                       "\n", AUDIT_ARCH_I386, AUDIT_ARCH_X86_64);
+               return 1;
+       }
+       if (install_filter(strtol(argv[1], NULL, 0), strtol(argv[2], NULL, 0),
+                          strtol(argv[3], NULL, 0)))
+               return 1;
+       execv(argv[4], &argv[4]);
+       printf("Failed to execv\n");
+       return 255;
+}