mnt: Update unprivileged remount test

- MNT_NODEV should be irrelevant except when reading back mount flags,
  no longer specify MNT_NODEV on remount.

- Test MNT_NODEV on devpts where it is meaningful even for unprivileged mounts.

- Add a test to verify that remount of a prexisting mount with the same flags
  is allowed and does not change those flags.

- Cleanup up the definitions of MS_REC, MS_RELATIME, MS_STRICTATIME that are used
  when the code is built in an environment without them.

- Correct the test error messages when tests fail.  There were not 5 tests
  that tested MS_RELATIME.

Cc: stable@vger.kernel.org
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>

1 files changed, 142 insertions, 30 deletions

diff --git a/tools/testing/selftests/mount/unprivileged-remount-test.c b/tools/testing/selftests/mount/unprivileged-remount-test.c
index 1b3ff2fda4d0..9669d375625a 100644
--- a/tools/testing/selftests/mount/unprivileged-remount-test.c
+++ b/tools/testing/selftests/mount/unprivileged-remount-test.c
@@ -6,6 +6,8 @@
 #include <sys/types.h>
 #include <sys/mount.h>
 #include <sys/wait.h>
+#include <sys/vfs.h>
+#include <sys/statvfs.h>
 #include <stdlib.h>
 #include <unistd.h>
 #include <fcntl.h>
@@ -32,11 +34,14 @@
 # define CLONE_NEWPID 0x20000000
 #endif
 
+#ifndef MS_REC
+# define MS_REC 16384
+#endif
 #ifndef MS_RELATIME
-#define MS_RELATIME (1 << 21)
+# define MS_RELATIME (1 << 21)
 #endif
 #ifndef MS_STRICTATIME
-#define MS_STRICTATIME (1 << 24)
+# define MS_STRICTATIME (1 << 24)
 #endif
 
 static void die(char *fmt, ...)
@@ -87,6 +92,45 @@ static void write_file(char *filename, char *fmt, ...)
         }
 }
 
+static int read_mnt_flags(const char *path)
+{
+        int ret;
+        struct statvfs stat;
+        int mnt_flags;
+
+        ret = statvfs(path, &stat);
+        if (ret != 0) {
+                die("statvfs of %s failed: %s\n",
+                        path, strerror(errno));
+        }
+        if (stat.f_flag & ~(ST_RDONLY | ST_NOSUID | ST_NODEV | \
+                        ST_NOEXEC | ST_NOATIME | ST_NODIRATIME | ST_RELATIME | \
+                        ST_SYNCHRONOUS | ST_MANDLOCK)) {
+                die("Unrecognized mount flags\n");
+        }
+        mnt_flags = 0;
+        if (stat.f_flag & ST_RDONLY)
+                mnt_flags |= MS_RDONLY;
+        if (stat.f_flag & ST_NOSUID)
+                mnt_flags |= MS_NOSUID;
+        if (stat.f_flag & ST_NODEV)
+                mnt_flags |= MS_NODEV;
+        if (stat.f_flag & ST_NOEXEC)
+                mnt_flags |= MS_NOEXEC;
+        if (stat.f_flag & ST_NOATIME)
+                mnt_flags |= MS_NOATIME;
+        if (stat.f_flag & ST_NODIRATIME)
+                mnt_flags |= MS_NODIRATIME;
+        if (stat.f_flag & ST_RELATIME)
+                mnt_flags |= MS_RELATIME;
+        if (stat.f_flag & ST_SYNCHRONOUS)
+                mnt_flags |= MS_SYNCHRONOUS;
+        if (stat.f_flag & ST_MANDLOCK)
+                mnt_flags |= ST_MANDLOCK;
+
+        return mnt_flags;
+}
+
 static void create_and_enter_userns(void)
 {
         uid_t uid;
@@ -118,7 +162,8 @@ static void create_and_enter_userns(void)
 }
 
 static
-bool test_unpriv_remount(int mount_flags, int remount_flags, int invalid_flags)
+bool test_unpriv_remount(const char *fstype, const char *mount_options,
+                         int mount_flags, int remount_flags, int invalid_flags)
 {
         pid_t child;
 
@@ -151,9 +196,11 @@ bool test_unpriv_remount(int mount_flags, int remount_flags, int invalid_flags)
                         strerror(errno));
         }
 
-        if (mount("testing", "/tmp", "ramfs", mount_flags, NULL) != 0) {
-                die("mount of /tmp failed: %s\n",
-                        strerror(errno));
+        if (mount("testing", "/tmp", fstype, mount_flags, mount_options) != 0) {
+                die("mount of %s with options '%s' on /tmp failed: %s\n",
+                    fstype,
+                    mount_options? mount_options : "",
+                    strerror(errno));
         }
 
         create_and_enter_userns();
@@ -181,62 +228,127 @@ bool test_unpriv_remount(int mount_flags, int remount_flags, int invalid_flags)
 
 static bool test_unpriv_remount_simple(int mount_flags)
 {
-        return test_unpriv_remount(mount_flags, mount_flags, 0);
+        return test_unpriv_remount("ramfs", NULL, mount_flags, mount_flags, 0);
 }
 
 static bool test_unpriv_remount_atime(int mount_flags, int invalid_flags)
 {
-        return test_unpriv_remount(mount_flags, mount_flags, invalid_flags);
+        return test_unpriv_remount("ramfs", NULL, mount_flags, mount_flags,
+                                   invalid_flags);
+}
+
+static bool test_priv_mount_unpriv_remount(void)
+{
+        pid_t child;
+        int ret;
+        const char *orig_path = "/dev";
+        const char *dest_path = "/tmp";
+        int orig_mnt_flags, remount_mnt_flags;
+
+        child = fork();
+        if (child == -1) {
+                die("fork failed: %s\n",
+                        strerror(errno));
+        }
+        if (child != 0) { /* parent */
+                pid_t pid;
+                int status;
+                pid = waitpid(child, &status, 0);
+                if (pid == -1) {
+                        die("waitpid failed: %s\n",
+                                strerror(errno));
+                }
+                if (pid != child) {
+                        die("waited for %d got %d\n",
+                                child, pid);
+                }
+                if (!WIFEXITED(status)) {
+                        die("child did not terminate cleanly\n");
+                }
+                return WEXITSTATUS(status) == EXIT_SUCCESS ? true : false;
+        }
+
+        orig_mnt_flags = read_mnt_flags(orig_path);
+
+        create_and_enter_userns();
+        ret = unshare(CLONE_NEWNS);
+        if (ret != 0) {
+                die("unshare(CLONE_NEWNS) failed: %s\n",
+                        strerror(errno));
+        }
+
+        ret = mount(orig_path, dest_path, "bind", MS_BIND | MS_REC, NULL);
+        if (ret != 0) {
+                die("recursive bind mount of %s onto %s failed: %s\n",
+                        orig_path, dest_path, strerror(errno));
+        }