selftests: mount: add nosymfollow tests

Add tests for the new 'nosymfollow' mount option.  We test to make sure
that symlink traversal fails with ELOOP when 'nosymfollow' is set, but
that readlink(2) and realpath(3) still work as expected.  We also verify
that statfs(2) correctly returns ST_NOSYMFOLLOW when we are mounted with
the 'nosymfollow' option.

Signed-off-by: Ross Zwisler <zwisler@google.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

diff --git a/tools/testing/selftests/mount/.gitignore b/tools/testing/selftests/mount/.gitignore
index 0bc64a6d4c1818d81226b3daef73c6ca54b9e0c5..17f2d8415162299634508cabd915a9395e896a33 100644 (file)
--- a/tools/testing/selftests/mount/.gitignore
+++ b/tools/testing/selftests/mount/.gitignore
@@ -1,2 +1,3 @@
 # SPDX-License-Identifier: GPL-2.0-only
 unprivileged-remount-test
+nosymfollow-test

diff --git a/tools/testing/selftests/mount/Makefile b/tools/testing/selftests/mount/Makefile
index 026890744215b614073397f61a67286f8584376c..2d9454841644aaa986d35579eba5025e37583c7d 100644 (file)
--- a/tools/testing/selftests/mount/Makefile
+++ b/tools/testing/selftests/mount/Makefile
@@ -3,7 +3,7 @@
 CFLAGS = -Wall \
          -O2
 
-TEST_PROGS := run_tests.sh
-TEST_GEN_FILES := unprivileged-remount-test
+TEST_PROGS := run_unprivileged_remount.sh run_nosymfollow.sh
+TEST_GEN_FILES := unprivileged-remount-test nosymfollow-test
 
 include ../lib.mk

diff --git a/tools/testing/selftests/mount/nosymfollow-test.c b/tools/testing/selftests/mount/nosymfollow-test.c
new file mode 100644 (file)
index 0000000..650d6d8
--- /dev/null
+++ b/tools/testing/selftests/mount/nosymfollow-test.c
@@ -0,0 +1,218 @@
+// SPDX-License-Identifier: GPL-2.0
+#define _GNU_SOURCE
+#include <errno.h>
+#include <fcntl.h>
+#include <limits.h>
+#include <sched.h>
+#include <stdarg.h>
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/mount.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <sys/vfs.h>
+#include <unistd.h>
+
+#ifndef MS_NOSYMFOLLOW
+# define MS_NOSYMFOLLOW 256     /* Do not follow symlinks */
+#endif
+
+#ifndef ST_NOSYMFOLLOW
+# define ST_NOSYMFOLLOW 0x2000  /* Do not follow symlinks */
+#endif
+
+#define DATA "/tmp/data"
+#define LINK "/tmp/symlink"
+#define TMP  "/tmp"
+
+static void die(char *fmt, ...)
+{
+       va_list ap;
+
+       va_start(ap, fmt);
+       vfprintf(stderr, fmt, ap);
+       va_end(ap);
+       exit(EXIT_FAILURE);
+}
+
+static void vmaybe_write_file(bool enoent_ok, char *filename, char *fmt,
+               va_list ap)
+{
+       ssize_t written;
+       char buf[4096];
+       int buf_len;
+       int fd;
+
+       buf_len = vsnprintf(buf, sizeof(buf), fmt, ap);
+       if (buf_len < 0)
+               die("vsnprintf failed: %s\n", strerror(errno));
+
+       if (buf_len >= sizeof(buf))
+               die("vsnprintf output truncated\n");
+
+       fd = open(filename, O_WRONLY);
+       if (fd < 0) {
+               if ((errno == ENOENT) && enoent_ok)
+                       return;
+               die("open of %s failed: %s\n", filename, strerror(errno));
+       }
+
+       written = write(fd, buf, buf_len);
+       if (written != buf_len) {
+               if (written >= 0) {
+                       die("short write to %s\n", filename);
+               } else {
+                       die("write to %s failed: %s\n",
+                               filename, strerror(errno));
+               }
+       }
+
+       if (close(fd) != 0)
+               die("close of %s failed: %s\n", filename, strerror(errno));
+}
+
+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 void create_and_enter_ns(void)
+{
+       uid_t uid = getuid();
+       gid_t gid = getgid();
+
+       if (unshare(CLONE_NEWUSER) != 0)
+               die("unshare(CLONE_NEWUSER) failed: %s\n", strerror(errno));
+
+       maybe_write_file("/proc/self/setgroups", "deny");
+       write_file("/proc/self/uid_map", "0 %d 1", uid);
+       write_file("/proc/self/gid_map", "0 %d 1", gid);
+
+       if (setgid(0) != 0)
+               die("setgid(0) failed %s\n", strerror(errno));
+       if (setuid(0) != 0)
+               die("setuid(0) failed %s\n", strerror(errno));
+
+       if (unshare(CLONE_NEWNS) != 0)
+               die("unshare(CLONE_NEWNS) failed: %s\n", strerror(errno));
+}
+
+static void setup_symlink(void)
+{
+       int data, err;
+
+       data = creat(DATA, O_RDWR);
+       if (data < 0)
+               die("creat failed: %s\n", strerror(errno));
+
+       err = symlink(DATA, LINK);
+       if (err < 0)
+               die("symlink failed: %s\n", strerror(errno));
+
+       if (close(data) != 0)
+               die("close of %s failed: %s\n", DATA, strerror(errno));
+}
+
+static void test_link_traversal(bool nosymfollow)
+{
+       int link;
+
+       link = open(LINK, 0, O_RDWR);
+       if (nosymfollow) {
+               if ((link != -1 || errno != ELOOP)) {
+                       die("link traversal unexpected result: %d, %s\n",
+                                       link, strerror(errno));
+               }
+       } else {
+               if (link < 0)
+                       die("link traversal failed: %s\n", strerror(errno));
+
+               if (close(link) != 0)
+                       die("close of link failed: %s\n", strerror(errno));
+       }
+}
+
+static void test_readlink(void)
+{
+       char buf[4096];
+       ssize_t ret;
+
+       bzero(buf, sizeof(buf));
+
+       ret = readlink(LINK, buf, sizeof(buf));
+       if (ret < 0)
+               die("readlink failed: %s\n", strerror(errno));
+       if (strcmp(buf, DATA) != 0)
+               die("readlink strcmp failed: '%s' '%s'\n", buf, DATA);
+}
+
+static void test_realpath(void)
+{
+       char *path = realpath(LINK, NULL);
+
+       if (!path)
+               die("realpath failed: %s\n", strerror(errno));
+       if (strcmp(path, DATA) != 0)
+               die("realpath strcmp failed\n");
+
+       free(path);
+}
+
+static void test_statfs(bool nosymfollow)
+{
+       struct statfs buf;
+       int ret;
+
+       ret = statfs(TMP, &buf);
+       if (ret)
+               die("statfs failed: %s\n", strerror(errno));
+
+       if (nosymfollow) {
+               if ((buf.f_flags & ST_NOSYMFOLLOW) == 0)
+                       die("ST_NOSYMFOLLOW not set on %s\n", TMP);
+       } else {
+               if ((buf.f_flags & ST_NOSYMFOLLOW) != 0)
+                       die("ST_NOSYMFOLLOW set on %s\n", TMP);
+       }
+}
+
+static void run_tests(bool nosymfollow)
+{
+       test_link_traversal(nosymfollow);
+       test_readlink();
+       test_realpath();
+       test_statfs(nosymfollow);
+}
+
+int main(int argc, char **argv)
+{
+       create_and_enter_ns();
+
+       if (mount("testing", TMP, "ramfs", 0, NULL) != 0)
+               die("mount failed: %s\n", strerror(errno));
+
+       setup_symlink();
+       run_tests(false);
+
+       if (mount("testing", TMP, "ramfs", MS_REMOUNT|MS_NOSYMFOLLOW, NULL) != 0)
+               die("remount failed: %s\n", strerror(errno));
+
+       run_tests(true);
+
+       return EXIT_SUCCESS;
+}

diff --git a/tools/testing/selftests/mount/run_nosymfollow.sh b/tools/testing/selftests/mount/run_nosymfollow.sh
new file mode 100755 (executable)
index 0000000..5fbbf03
--- /dev/null
+++ b/tools/testing/selftests/mount/run_nosymfollow.sh
@@ -0,0 +1,4 @@
+#!/bin/bash
+# SPDX-License-Identifier: GPL-2.0
+
+./nosymfollow-test

diff --git a/tools/testing/selftests/mount/run_tests.sh b/tools/testing/selftests/mount/run_tests.sh
deleted file mode 100755 (executable)
index 4ab8f50..0000000
--- a/tools/testing/selftests/mount/run_tests.sh
+++ /dev/null
@@ -1,12 +0,0 @@
-#!/bin/bash
-# SPDX-License-Identifier: GPL-2.0
-# Kselftest framework requirement - SKIP code is 4.
-ksft_skip=4
-
-# Run mount selftests
-if [ -f /proc/self/uid_map ] ; then
-       ./unprivileged-remount-test ;
-else
-       echo "WARN: No /proc/self/uid_map exist, test skipped." ;
-       exit $ksft_skip
-fi

diff --git a/tools/testing/selftests/mount/run_unprivileged_remount.sh b/tools/testing/selftests/mount/run_unprivileged_remount.sh
new file mode 100755 (executable)
index 0000000..4ab8f50
--- /dev/null
+++ b/tools/testing/selftests/mount/run_unprivileged_remount.sh
@@ -0,0 +1,12 @@
+#!/bin/bash
+# SPDX-License-Identifier: GPL-2.0
+# Kselftest framework requirement - SKIP code is 4.
+ksft_skip=4
+
+# Run mount selftests
+if [ -f /proc/self/uid_map ] ; then
+       ./unprivileged-remount-test ;
+else
+       echo "WARN: No /proc/self/uid_map exist, test skipped." ;
+       exit $ksft_skip
+fi