ext4: add support for multiple mount protection

Prevent an ext4 filesystem from being mounted multiple times.
A sequence number is stored on disk and is periodically updated (every 5
seconds by default) by a mounted filesystem.
At mount time, we now wait for s_mmp_update_interval seconds to make sure
that the MMP sequence does not change.
In case of failure, the nodename, bdevname and the time at which the MMP
block was last updated is displayed.

Signed-off-by: Andreas Dilger <adilger@whamcloud.com>
Signed-off-by: Johann Lombardi <johann@whamcloud.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

1 files changed, 17 insertions, 1 deletions

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 266174b268cc..d9937df7f5cf 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -822,6 +822,8 @@ static void ext4_put_super(struct super_block *sb)
                 invalidate_bdev(sbi->journal_bdev);
                 ext4_blkdev_remove(sbi);
         }
+        if (sbi->s_mmp_tsk)
+                kthread_stop(sbi->s_mmp_tsk);
         sb->s_fs_info = NULL;
         /*
          * Now that we are completely done shutting down the
@@ -3486,6 +3488,11 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
                           EXT4_HAS_INCOMPAT_FEATURE(sb,
                                     EXT4_FEATURE_INCOMPAT_RECOVER));
 
+        if (EXT4_HAS_INCOMPAT_FEATURE(sb, EXT4_FEATURE_INCOMPAT_MMP) &&
+            !(sb->s_flags & MS_RDONLY))
+                if (ext4_multi_mount_protect(sb, le64_to_cpu(es->s_mmp_block)))
+                        goto failed_mount3;
+
         /*
          * The first inode we look at is the journal inode.  Don't try
          * root first: it may be modified in the journal!
@@ -3733,6 +3740,8 @@ failed_mount3:
         percpu_counter_destroy(&sbi->s_freeinodes_counter);
         percpu_counter_destroy(&sbi->s_dirs_counter);
         percpu_counter_destroy(&sbi->s_dirtyblocks_counter);
+        if (sbi->s_mmp_tsk)
+                kthread_stop(sbi->s_mmp_tsk);
 failed_mount2:
         for (i = 0; i < db_count; i++)
                 brelse(sbi->s_group_desc[i]);
@@ -4268,7 +4277,7 @@ static int ext4_remount(struct super_block *sb, int *flags, char *data)
         int enable_quota = 0;
         ext4_group_t g;
         unsigned int journal_ioprio = DEFAULT_JOURNAL_IOPRIO;
-        int err;
+        int err = 0;
 #ifdef CONFIG_QUOTA
         int i;
 #endif
@@ -4394,6 +4403,13 @@ static int ext4_remount(struct super_block *sb, int *flags, char *data)
                                 goto restore_opts;
                         if (!ext4_setup_super(sb, es, 0))
                                 sb->s_flags &= ~MS_RDONLY;
+                        if (EXT4_HAS_INCOMPAT_FEATURE(sb,
+                                                     EXT4_FEATURE_INCOMPAT_MMP))
+                                if (ext4_multi_mount_protect(sb,
+                                                le64_to_cpu(es->s_mmp_block))) {
+                                        err = -EROFS;
+                                        goto restore_opts;
+                                }
                         enable_quota = 1;
                 }
         }