tests: add a test for SECCOMP_MODE_FILTER decoding

* tests/seccomp.c: New file.
* tests/seccomp.test: New test.
* tests/Makefile.am (check_PROGRAMS): Add seccomp.
(TESTS): Add seccomp.test.
* tests/.gitignore: Add seccomp.

tests/.gitignore

@@ -12,6 +12,7 @@ netlink_inet_diag
 netlink_unix_diag
 pc
 scm_rights
+seccomp
 select
 set_ptracer_any
 sigaction

tests/Makefile.am

@@ -21,6 +21,7 @@ check_PROGRAMS = \
 	netlink_unix_diag \
 	pc \
 	scm_rights \
+	seccomp \
 	select \
 	set_ptracer_any \
 	sigaction \
@@ -56,6 +57,7 @@ TESTS = \
 	ipc_shm.test \
 	ipc_sem.test \
 	scm_rights-fd.test \
+	seccomp.test \
 	select.test \
 	sigaction.test \
 	sigreturn.test \

tests/seccomp.c

@@ -0,0 +1,113 @@
+#ifdef HAVE_CONFIG_H
+# include "config.h"
+#endif
+
+#include <stddef.h>
+#include <unistd.h>
+#include <stdio.h>
+#include <errno.h>
+#include <sys/syscall.h>
+
+#ifdef HAVE_PRCTL
+# include <sys/prctl.h>
+#endif
+#ifdef HAVE_LINUX_SECCOMP_H
+# include <linux/seccomp.h>
+#endif
+#ifdef HAVE_LINUX_FILTER_H
+# include <linux/filter.h>
+#endif
+
+#if defined HAVE_PRCTL \
+ && defined PR_SET_NO_NEW_PRIVS \
+ && defined PR_SET_SECCOMP \
+ && defined SECCOMP_MODE_FILTER \
+ && defined SECCOMP_RET_ERRNO \
+ && defined BPF_JUMP \
+ && defined BPF_STMT
+
+#define SOCK_FILTER_ALLOW_SYSCALL(nr) \
+		BPF_JUMP(BPF_JMP | BPF_K | BPF_JEQ, __NR_ ## nr, 0, 1), \
+		BPF_STMT(BPF_RET | BPF_K, SECCOMP_RET_ALLOW)
+
+#define SOCK_FILTER_DENY_SYSCALL(nr, err) \
+		BPF_JUMP(BPF_JMP | BPF_K | BPF_JEQ, __NR_ ## nr, 0, 1), \
+		BPF_STMT(BPF_RET | BPF_K, SECCOMP_RET_ERRNO | (SECCOMP_RET_DATA & (err)))
+
+#define SOCK_FILTER_KILL_PROCESS \
+		BPF_STMT(BPF_RET | BPF_K, SECCOMP_RET_KILL)
+
+#define PRINT_ALLOW_SYSCALL(nr) \
+	printf("BPF_JUMP(BPF_JMP | BPF_K | BPF_JEQ, %#x, 0, 0x1), " \
+	       "BPF_STMT(BPF_RET | BPF_K, SECCOMP_RET_ALLOW), ", \
+	       __NR_ ## nr)
+
+#define PRINT_DENY_SYSCALL(nr, err) \
+	printf("BPF_JUMP(BPF_JMP | BPF_K | BPF_JEQ, %#x, 0, 0x1), " \
+	       "BPF_STMT(BPF_RET | BPF_K, SECCOMP_RET_ERRNO | %#x), ", \
+	       __NR_ ## nr, err)
+
+static const struct sock_filter filter[] = {
+	/* load syscall number */
+	BPF_STMT(BPF_LD | BPF_W | BPF_ABS, offsetof(struct seccomp_data, nr)),
+
+	/* allow syscalls */
+	SOCK_FILTER_ALLOW_SYSCALL(close),
+	SOCK_FILTER_ALLOW_SYSCALL(exit),
+	SOCK_FILTER_ALLOW_SYSCALL(exit_group),
+
+	/* deny syscalls */
+	SOCK_FILTER_DENY_SYSCALL(sync, EBUSY),
+	SOCK_FILTER_DENY_SYSCALL(setsid, EPERM),
+
+	/* kill process */
+	SOCK_FILTER_KILL_PROCESS
+};
+
+static const struct sock_fprog prog = {
+	.len = sizeof(filter) / sizeof(filter[0]),
+	.filter = (struct sock_filter *) filter,
+};
+
+int
+main(void)
+{
+	int fds[2];
+
+	puts("prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0)  = 0");
+
+	printf("prctl(PR_SET_SECCOMP, SECCOMP_MODE_FILTER, [");
+
+	printf("BPF_STMT(BPF_LD | BPF_W | BPF_ABS, %#x), ",
+	       (unsigned) offsetof(struct seccomp_data, nr));
+
+	PRINT_ALLOW_SYSCALL(close);
+	PRINT_ALLOW_SYSCALL(exit);
+	PRINT_ALLOW_SYSCALL(exit_group);
+
+	PRINT_DENY_SYSCALL(sync, EBUSY),
+	PRINT_DENY_SYSCALL(setsid, EPERM),
+
+	printf("BPF_STMT(BPF_RET | BPF_K, SECCOMP_RET_KILL)");
+
+	puts("]) = 0");
+	puts("+++ exited with 0 +++");
+
+	fflush(stdout);
+	close(0);
+	close(1);
+
+	if (pipe(fds) ||
+	    prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0) ||
+	    prctl(PR_SET_SECCOMP, SECCOMP_MODE_FILTER, &prog) ||
+	    close(0) || close(1))
+		_exit(77);
+
+	_exit(0);
+}
+
+#else
+
+int main(void) { return 77; }
+
+#endif

tests/seccomp.test

@@ -0,0 +1,15 @@
+#!/bin/sh
+
+# Check how SECCOMP_MODE_FILTER is decoded.
+
+. "${srcdir=.}/init.sh"
+
+OUT="$LOG.out"
+
+run_prog > /dev/null
+run_strace -veprctl $args > "$OUT"
+match_diff "$LOG" "$OUT"
+
+rm -f "$OUT"
+
+exit 0