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Date: Mon, 24 Aug 2015 16:40:57 -0700
From: Kees Cook <keescook@...omium.org>
To: Andy Lutomirski <luto@...nel.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
Christoph Lameter <cl@...ux.com>,
James Morris <jmorris@...ei.org>,
Andrew Morton <akpm@...uxfoundation.org>,
"Serge E. Hallyn" <serge@...lyn.com>,
Serge Hallyn <serge.hallyn@...ntu.com>,
James Morris <james.l.morris@...cle.com>,
Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>,
"Ted Ts'o" <tytso@....edu>, "Andrew G. Morgan" <morgan@...nel.org>,
Linux API <linux-api@...r.kernel.org>,
Mimi Zohar <zohar@...ux.vnet.ibm.com>,
Michael Kerrisk <mtk.manpages@...il.com>,
Austin S Hemmelgarn <ahferroin7@...il.com>,
linux-security-module <linux-security-module@...r.kernel.org>,
Aaron Jones <aaronmdjones@...il.com>,
Serge Hallyn <serge.hallyn@...onical.com>,
LKML <linux-kernel@...r.kernel.org>,
Markku Savela <msa@...h.iki.fi>,
Jonathan Corbet <corbet@....net>
Subject: Re: [PATCH -mm] selftests/capabilities: Add tests for capability evolution
On Mon, Aug 24, 2015 at 4:03 PM, Andy Lutomirski <luto@...nel.org> wrote:
> This test focuses on ambient capabilities. It requires either root
> or the ability to create user namespaces. Some of the test cases
> will be skipped for nonroot users.
>
> Signed-off-by: Andy Lutomirski <luto@...nel.org>
Looks great! Thanks for this!
Acked-by: Kees Cook <keescook@...omium.org>
-Kees
> ---
>
> I took taking advantage of the extra week to make my test case work :)
>
> tools/testing/selftests/capabilities/.gitignore | 2 +
> tools/testing/selftests/capabilities/Makefile | 19 +
> tools/testing/selftests/capabilities/test_execve.c | 427 +++++++++++++++++++++
> .../testing/selftests/capabilities/validate_cap.c | 73 ++++
> 4 files changed, 521 insertions(+)
> create mode 100644 tools/testing/selftests/capabilities/.gitignore
> create mode 100644 tools/testing/selftests/capabilities/Makefile
> create mode 100644 tools/testing/selftests/capabilities/test_execve.c
> create mode 100644 tools/testing/selftests/capabilities/validate_cap.c
>
> diff --git a/tools/testing/selftests/capabilities/.gitignore b/tools/testing/selftests/capabilities/.gitignore
> new file mode 100644
> index 000000000000..b732dd0d4738
> --- /dev/null
> +++ b/tools/testing/selftests/capabilities/.gitignore
> @@ -0,0 +1,2 @@
> +test_execve
> +validate_cap
> diff --git a/tools/testing/selftests/capabilities/Makefile b/tools/testing/selftests/capabilities/Makefile
> new file mode 100644
> index 000000000000..5b90ed14cccb
> --- /dev/null
> +++ b/tools/testing/selftests/capabilities/Makefile
> @@ -0,0 +1,19 @@
> +all:
> +
> +include ../lib.mk
> +
> +.PHONY: all clean
> +
> +TARGETS := validate_cap test_execve
> +TEST_PROGS := test_execve
> +
> +CFLAGS := -O2 -g -std=gnu99 -Wall -lcap-ng
> +
> +all: $(TARGETS)
> +
> +clean:
> + $(RM) $(TARGETS)
> +
> +$(TARGETS): %: %.c
> + $(CC) -o $@ $(CFLAGS) $(EXTRA_CFLAGS) $^ -lrt -ldl
> +
> diff --git a/tools/testing/selftests/capabilities/test_execve.c b/tools/testing/selftests/capabilities/test_execve.c
> new file mode 100644
> index 000000000000..10a21a958aaf
> --- /dev/null
> +++ b/tools/testing/selftests/capabilities/test_execve.c
> @@ -0,0 +1,427 @@
> +#define _GNU_SOURCE
> +
> +#include <cap-ng.h>
> +#include <err.h>
> +#include <linux/capability.h>
> +#include <stdbool.h>
> +#include <string.h>
> +#include <stdio.h>
> +#include <fcntl.h>
> +#include <errno.h>
> +#include <stdarg.h>
> +#include <sched.h>
> +#include <sys/mount.h>
> +#include <limits.h>
> +#include <libgen.h>
> +#include <malloc.h>
> +#include <sys/wait.h>
> +#include <sys/prctl.h>
> +#include <sys/stat.h>
> +
> +#ifndef PR_CAP_AMBIENT
> +#define PR_CAP_AMBIENT 47
> +# define PR_CAP_AMBIENT_IS_SET 1
> +# define PR_CAP_AMBIENT_RAISE 2
> +# define PR_CAP_AMBIENT_LOWER 3
> +# define PR_CAP_AMBIENT_CLEAR_ALL 4
> +#endif
> +
> +static int nerrs;
> +
> +static void vmaybe_write_file(bool enoent_ok, char *filename, char *fmt, va_list ap)
> +{
> + char buf[4096];
> + int fd;
> + ssize_t written;
> + int buf_len;
> +
> + buf_len = vsnprintf(buf, sizeof(buf), fmt, ap);
> + if (buf_len < 0) {
> + err(1, "vsnprintf failed");
> + }
> + if (buf_len >= sizeof(buf)) {
> + errx(1, "vsnprintf output truncated");
> + }
> +
> + fd = open(filename, O_WRONLY);
> + if (fd < 0) {
> + if ((errno == ENOENT) && enoent_ok)
> + return;
> + err(1, "open of %s failed", filename);
> + }
> + written = write(fd, buf, buf_len);
> + if (written != buf_len) {
> + if (written >= 0) {
> + errx(1, "short write to %s", filename);
> + } else {
> + err(1, "write to %s failed", filename);
> + }
> + }
> + if (close(fd) != 0) {
> + err(1, "close of %s failed", filename);
> + }
> +}
> +
> +static void maybe_write_file(char *filename, char *fmt, ...)
> +{
> + va_list ap;
> +
> + va_start(ap, fmt);
> + vmaybe_write_file(true, filename, fmt, ap);
> + va_end(ap);
> +}
> +
> +static void write_file(char *filename, char *fmt, ...)
> +{
> + va_list ap;
> +
> + va_start(ap, fmt);
> + vmaybe_write_file(false, filename, fmt, ap);
> + va_end(ap);
> +}
> +
> +static bool create_and_enter_ns(uid_t inner_uid)
> +{
> + uid_t outer_uid;
> + gid_t outer_gid;
> + int i;
> + bool have_outer_privilege;
> +
> + outer_uid = getuid();
> + outer_gid = getgid();
> +
> + /*
> + * TODO: If we're already root, we could skip creating the userns.
> + */
> +
> + if (unshare(CLONE_NEWNS) == 0) {
> + printf("[NOTE]\tUsing global UIDs for tests\n");
> + if (prctl(PR_SET_KEEPCAPS, 1, 0, 0, 0) != 0)
> + err(1, "PR_SET_KEEPCAPS");
> + if (setresuid(inner_uid, inner_uid, -1) != 0)
> + err(1, "setresuid");
> +
> + // Re-enable effective caps
> + capng_get_caps_process();
> + for (i = 0; i < CAP_LAST_CAP; i++)
> + if (capng_have_capability(CAPNG_PERMITTED, i))
> + capng_update(CAPNG_ADD, CAPNG_EFFECTIVE, i);
> + if (capng_apply(CAPNG_SELECT_CAPS) != 0)
> + err(1, "capng_apply");
> +
> + have_outer_privilege = true;
> + } else if (unshare(CLONE_NEWUSER | CLONE_NEWNS) == 0) {
> + printf("[NOTE]\tUsing a user namespace for tests\n");
> + maybe_write_file("/proc/self/setgroups", "deny");
> + write_file("/proc/self/uid_map", "%d %d 1", inner_uid, outer_uid);
> + write_file("/proc/self/gid_map", "0 %d 1", outer_gid);
> +
> + have_outer_privilege = false;
> + } else {
> + errx(1, "must be root or be able to create a userns");
> + }
> +
> + if (mount("none", "/", NULL, MS_REC | MS_PRIVATE, NULL) != 0)
> + err(1, "remount everything private");
> +
> + return have_outer_privilege;
> +}
> +
> +static void chdir_to_tmpfs(void)
> +{
> + char cwd[PATH_MAX];
> + if (getcwd(cwd, sizeof(cwd)) != cwd)
> + err(1, "getcwd");
> +
> + if (mount("private_tmp", ".", "tmpfs", 0, "mode=0777") != 0)
> + err(1, "mount private tmpfs");
> +
> + if (chdir(cwd) != 0)
> + err(1, "chdir to private tmpfs");
> +
> + if (umount2(".", MNT_DETACH) != 0)
> + err(1, "detach private tmpfs");
> +}
> +
> +static void copy_fromat_to(int fromfd, const char *fromname, const char *toname)
> +{
> + int from = openat(fromfd, fromname, O_RDONLY);
> + if (from == -1)
> + err(1, "open copy source");
> +
> + int to = open(toname, O_CREAT | O_WRONLY | O_EXCL, 0700);
> +
> + while (true) {
> + char buf[4096];
> + ssize_t sz = read(from, buf, sizeof(buf));
> + if (sz == 0)
> + break;
> + if (sz < 0)
> + err(1, "read");
> +
> + if (write(to, buf, sz) != sz)
> + err(1, "write"); /* no short writes on tmpfs */
> + }
> +
> + close(from);
> + close(to);
> +}
> +
> +static bool fork_wait(void)
> +{
> + pid_t child = fork();
> + if (child == 0) {
> + nerrs = 0;
> + return true;
> + } else if (child > 0) {
> + int status;
> + if (waitpid(child, &status, 0) != child ||
> + !WIFEXITED(status)) {
> + printf("[FAIL]\tChild died\n");
> + nerrs++;
> + } else if (WEXITSTATUS(status) != 0) {
> + printf("[FAIL]\tChild failed\n");
> + nerrs++;
> + } else {
> + printf("[OK]\tChild succeeded\n");
> + }
> +
> + return false;
> + } else {
> + err(1, "fork");
> + }
> +}
> +
> +static void exec_other_validate_cap(const char *name,
> + bool eff, bool perm, bool inh, bool ambient)
> +{
> + execl(name, name, (eff ? "1" : "0"),
> + (perm ? "1" : "0"), (inh ? "1" : "0"), (ambient ? "1" : "0"),
> + NULL);
> + err(1, "execl");
> +}
> +
> +static void exec_validate_cap(bool eff, bool perm, bool inh, bool ambient)
> +{
> + exec_other_validate_cap("./validate_cap", eff, perm, inh, ambient);
> +}
> +
> +static int do_tests(int uid, const char *our_path)
> +{
> + bool have_outer_privilege = create_and_enter_ns(uid);
> +
> + int ourpath_fd = open(our_path, O_RDONLY | O_DIRECTORY);
> + if (ourpath_fd == -1)
> + err(1, "open '%s'", our_path);
> +
> + chdir_to_tmpfs();
> +
> + copy_fromat_to(ourpath_fd, "validate_cap", "validate_cap");
> +
> + if (have_outer_privilege) {
> + uid_t gid = getegid();
> +
> + copy_fromat_to(ourpath_fd, "validate_cap",
> + "validate_cap_suidroot");
> + if (chown("validate_cap_suidroot", 0, -1) != 0)
> + err(1, "chown");
> + if (chmod("validate_cap_suidroot", S_ISUID | 0700) != 0)
> + err(1, "chmod");
> +
> + copy_fromat_to(ourpath_fd, "validate_cap",
> + "validate_cap_suidnonroot");
> + if (chown("validate_cap_suidnonroot", uid + 1, -1) != 0)
> + err(1, "chown");
> + if (chmod("validate_cap_suidnonroot", S_ISUID | 0700) != 0)
> + err(1, "chmod");
> +
> + copy_fromat_to(ourpath_fd, "validate_cap",
> + "validate_cap_sgidroot");
> + if (chown("validate_cap_sgidroot", -1, 0) != 0)
> + err(1, "chown");
> + if (chmod("validate_cap_sgidroot", S_ISGID | 0710) != 0)
> + err(1, "chmod");
> +
> + copy_fromat_to(ourpath_fd, "validate_cap",
> + "validate_cap_sgidnonroot");
> + if (chown("validate_cap_sgidnonroot", -1, gid + 1) != 0)
> + err(1, "chown");
> + if (chmod("validate_cap_sgidnonroot", S_ISGID | 0710) != 0)
> + err(1, "chmod");
> +}
> +
> + capng_get_caps_process();
> +
> + /* Make sure that i starts out clear */
> + capng_update(CAPNG_DROP, CAPNG_INHERITABLE, CAP_NET_BIND_SERVICE);
> + if (capng_apply(CAPNG_SELECT_CAPS) != 0)
> + err(1, "capng_apply");
> +
> + if (uid == 0) {
> + printf("[RUN]\tRoot => ep\n");
> + if (fork_wait())
> + exec_validate_cap(true, true, false, false);
> + } else {
> + printf("[RUN]\tNon-root => no caps\n");
> + if (fork_wait())
> + exec_validate_cap(false, false, false, false);
> + }
> +
> + printf("[OK]\tCheck cap_ambient manipulation rules\n");
> +
> + /* We should not be able to add ambient caps yet. */
> + if (prctl(PR_CAP_AMBIENT, PR_CAP_AMBIENT_RAISE, CAP_NET_BIND_SERVICE, 0, 0, 0) != -1 || errno != EPERM) {
> + if (errno == EINVAL)
> + printf("[FAIL]\tPR_CAP_AMBIENT_RAISE isn't supported\n");
> + else
> + printf("[FAIL]\tPR_CAP_AMBIENT_RAISE should have failed eith EPERM on a non-inheritable cap\n");
> + return 1;
> + }
> + printf("[OK]\tPR_CAP_AMBIENT_RAISE failed on non-inheritable cap\n");
> +
> + capng_update(CAPNG_ADD, CAPNG_INHERITABLE, CAP_NET_RAW);
> + capng_update(CAPNG_DROP, CAPNG_PERMITTED, CAP_NET_RAW);
> + capng_update(CAPNG_DROP, CAPNG_EFFECTIVE, CAP_NET_RAW);
> + if (capng_apply(CAPNG_SELECT_CAPS) != 0)
> + err(1, "capng_apply");
> + if (prctl(PR_CAP_AMBIENT, PR_CAP_AMBIENT_RAISE, CAP_NET_RAW, 0, 0, 0) != -1 || errno != EPERM) {
> + printf("[FAIL]\tPR_CAP_AMBIENT_RAISE should have failed on a non-permitted cap\n");
> + return 1;
> + }
> + printf("[OK]\tPR_CAP_AMBIENT_RAISE failed on non-permitted cap\n");
> +
> + capng_update(CAPNG_ADD, CAPNG_INHERITABLE, CAP_NET_BIND_SERVICE);
> + if (capng_apply(CAPNG_SELECT_CAPS) != 0)
> + err(1, "capng_apply");
> + if (prctl(PR_CAP_AMBIENT, PR_CAP_AMBIENT_RAISE, CAP_NET_BIND_SERVICE, 0, 0, 0) != 0) {
> + printf("[FAIL]\tPR_CAP_AMBIENT_RAISE should have succeeded\n");
> + return 1;
> + }
> + printf("[OK]\tPR_CAP_AMBIENT_RAISE worked\n");
> +
> + if (prctl(PR_CAP_AMBIENT, PR_CAP_AMBIENT_IS_SET, CAP_NET_BIND_SERVICE, 0, 0, 0) != 1) {
> + printf("[FAIL]\tPR_CAP_AMBIENT_IS_SET is broken\n");
> + return 1;
> + }
> +
> + if (prctl(PR_CAP_AMBIENT, PR_CAP_AMBIENT_CLEAR_ALL, 0, 0, 0, 0) != 0)
> + err(1, "PR_CAP_AMBIENT_CLEAR_ALL");
> +
> + if (prctl(PR_CAP_AMBIENT, PR_CAP_AMBIENT_IS_SET, CAP_NET_BIND_SERVICE, 0, 0, 0) != 0) {
> + printf("[FAIL]\tPR_CAP_AMBIENT_CLEAR_ALL didn't work\n");
> + return 1;
> + }
> +
> + if (prctl(PR_CAP_AMBIENT, PR_CAP_AMBIENT_RAISE, CAP_NET_BIND_SERVICE, 0, 0, 0) != 0)
> + err(1, "PR_CAP_AMBIENT_RAISE");
> +
> + capng_update(CAPNG_DROP, CAPNG_INHERITABLE, CAP_NET_BIND_SERVICE);
> + if (capng_apply(CAPNG_SELECT_CAPS) != 0)
> + err(1, "capng_apply");
> +
> + if (prctl(PR_CAP_AMBIENT, PR_CAP_AMBIENT_IS_SET, CAP_NET_BIND_SERVICE, 0, 0, 0) != 0) {
> + printf("[FAIL]\tDropping I should have dropped A\n");
> + return 1;
> + }
> +
> + printf("[OK]\tBasic manipulation appears to work\n");
> +
> + capng_update(CAPNG_ADD, CAPNG_INHERITABLE, CAP_NET_BIND_SERVICE);
> + if (capng_apply(CAPNG_SELECT_CAPS) != 0)
> + err(1, "capng_apply");
> + if (uid == 0) {
> + printf("[RUN]\tRoot +i => eip\n");
> + if (fork_wait())
> + exec_validate_cap(true, true, true, false);
> + } else {
> + printf("[RUN]\tNon-root +i => i\n");
> + if (fork_wait())
> + exec_validate_cap(false, false, true, false);
> + }
> +
> + if (prctl(PR_CAP_AMBIENT, PR_CAP_AMBIENT_RAISE, CAP_NET_BIND_SERVICE, 0, 0, 0) != 0)
> + err(1, "PR_CAP_AMBIENT_RAISE");
> +
> + printf("[RUN]\tUID %d +ia => eipa\n", uid);
> + if (fork_wait())
> + exec_validate_cap(true, true, true, true);
> +
> + /* The remaining tests need real privilege */
> +
> + if (!have_outer_privilege) {
> + printf("[SKIP]\tSUID/SGID tests (needs privilege)\n");
> + goto done;
> + }
> +
> + if (uid == 0) {
> + printf("[RUN]\tRoot +ia, suidroot => eipa\n");
> + if (fork_wait())
> + exec_other_validate_cap("./validate_cap_suidroot",
> + true, true, true, true);
> +
> + printf("[RUN]\tRoot +ia, suidnonroot => ip\n");
> + if (fork_wait())
> + exec_other_validate_cap("./validate_cap_suidnonroot",
> + false, true, true, false);
> +
> + printf("[RUN]\tRoot +ia, sgidroot => eipa\n");
> + if (fork_wait())
> + exec_other_validate_cap("./validate_cap_sgidroot",
> + true, true, true, true);
> +
> + if (fork_wait()) {
> + printf("[RUN]\tRoot, gid != 0, +ia, sgidroot => eip\n");
> + if (setresgid(1, 1, 1) != 0)
> + err(1, "setresgid");
> + exec_other_validate_cap("./validate_cap_sgidroot",
> + true, true, true, false);
> + }
> +
> + printf("[RUN]\tRoot +ia, sgidnonroot => eip\n");
> + if (fork_wait())
> + exec_other_validate_cap("./validate_cap_sgidnonroot",
> + true, true, true, false);
> + } else {
> + printf("[RUN]\tNon-root +ia, sgidnonroot => i\n");
> + exec_other_validate_cap("./validate_cap_sgidnonroot",
> + false, false, true, false);
> +
> + if (fork_wait()) {
> + printf("[RUN]\tNon-root +ia, sgidroot => i\n");
> + if (setresgid(1, 1, 1) != 0)
> + err(1, "setresgid");
> + exec_other_validate_cap("./validate_cap_sgidroot",
> + false, false, true, false);
> + }
> + }
> +
> +done:
> + return nerrs ? 1 : 0;
> +}
> +
> +int main(int argc, char **argv)
> +{
> + char *tmp1, *tmp2, *our_path;
> +
> + /* Find our path */
> + tmp1 = strdup(argv[0]);
> + if (!tmp1)
> + err(1, "strdup");
> + tmp2 = dirname(tmp1);
> + our_path = strdup(tmp2);
> + if (!our_path)
> + err(1, "strdup");
> + free(tmp1);
> +
> + if (fork_wait()) {
> + printf("[RUN]\t+++ Tests with uid == 0 +++\n");
> + return do_tests(0, our_path);
> + }
> +
> + if (fork_wait()) {
> + printf("[RUN]\t+++ Tests with uid != 0 +++\n");
> + return do_tests(1, our_path);
> + }
> +
> + return nerrs ? 1 : 0;
> +}
> diff --git a/tools/testing/selftests/capabilities/validate_cap.c b/tools/testing/selftests/capabilities/validate_cap.c
> new file mode 100644
> index 000000000000..dd3c45f7b23c
> --- /dev/null
> +++ b/tools/testing/selftests/capabilities/validate_cap.c
> @@ -0,0 +1,73 @@
> +#include <cap-ng.h>
> +#include <err.h>
> +#include <linux/capability.h>
> +#include <stdbool.h>
> +#include <string.h>
> +#include <stdio.h>
> +#include <sys/prctl.h>
> +#include <sys/auxv.h>
> +
> +#ifndef PR_CAP_AMBIENT
> +#define PR_CAP_AMBIENT 47
> +# define PR_CAP_AMBIENT_IS_SET 1
> +# define PR_CAP_AMBIENT_RAISE 2
> +# define PR_CAP_AMBIENT_LOWER 3
> +# define PR_CAP_AMBIENT_CLEAR_ALL 4
> +#endif
> +
> +#if __GLIBC__ > 2 || (__GLIBC__ == 2 && __GLIBC_MINOR__ >= 19)
> +# define HAVE_GETAUXVAL
> +#endif
> +
> +static bool bool_arg(char **argv, int i)
> +{
> + if (!strcmp(argv[i], "0"))
> + return false;
> + else if (!strcmp(argv[i], "1"))
> + return true;
> + else
> + errx(1, "wrong argv[%d]", i);
> +}
> +
> +int main(int argc, char **argv)
> +{
> + const char *atsec = "";
> +
> + /*
> + * Be careful just in case a setgid or setcapped copy of this
> + * helper gets out.
> + */
> +
> + if (argc != 5)
> + errx(1, "wrong argc");
> +
> +#ifdef HAVE_GETAUXVAL
> + if (getauxval(AT_SECURE))
> + atsec = " (AT_SECURE is set)";
> + else
> + atsec = " (AT_SECURE is not set)";
> +#endif
> +
> + capng_get_caps_process();
> +
> + if (capng_have_capability(CAPNG_EFFECTIVE, CAP_NET_BIND_SERVICE) != bool_arg(argv, 1)) {
> + printf("[FAIL]\tWrong effective state%s\n", atsec);
> + return 1;
> + }
> + if (capng_have_capability(CAPNG_PERMITTED, CAP_NET_BIND_SERVICE) != bool_arg(argv, 2)) {
> + printf("[FAIL]\tWrong permitted state%s\n", atsec);
> + return 1;
> + }
> + if (capng_have_capability(CAPNG_INHERITABLE, CAP_NET_BIND_SERVICE) != bool_arg(argv, 3)) {
> + printf("[FAIL]\tWrong inheritable state%s\n", atsec);
> + return 1;
> + }
> +
> + if (prctl(PR_CAP_AMBIENT, PR_CAP_AMBIENT_IS_SET, CAP_NET_BIND_SERVICE, 0, 0, 0) != bool_arg(argv, 4)) {
> + printf("[FAIL]\tWrong ambient state%s\n", atsec);
> + return 1;
> + }
> +
> + printf("[OK]\tCapabilities after execve were correct\n");
> + return 0;
> +}
> --
> 2.4.3
>
--
Kees Cook
Chrome OS Security
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