[PATCH 2/2] ext4: add ext4_iget_normal() which is to be used for dir tree lookups

[Theodore Ts'o <tytso@mit.edu>]

If there is a corrupted file system which has directory entries that
point at reserved, metadata inodes, prohibit them from being used by
treating them the same way we treat Boot Loader inodes --- that is,
mark them to be bad inodes.  This prohibits them from being opened,
deleted, or modified via chmod, chown, utimes, etc.

In particular, this prevents a corrupted file system which has a
directory entry which points at the journal inode from being deleted
and being released, after which point Much Hilarity Ensues.

Reported-by: Sami Liedes <sami.liedes@iki.fi>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
---
 fs/ext4/ext4.h  |  1 +
 fs/ext4/inode.c | 10 ++++++++++
 fs/ext4/namei.c |  4 ++--
 fs/ext4/super.c |  2 +-
 4 files changed, 14 insertions(+), 3 deletions(-)

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 1eb5b7b..012e89b 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -2109,6 +2109,7 @@ int do_journal_get_write_access(handle_t *handle,
 #define CONVERT_INLINE_DATA	 2
 
 extern struct inode *ext4_iget(struct super_block *, unsigned long);
+extern struct inode *ext4_iget_normal(struct super_block *, unsigned long);
 extern int  ext4_write_inode(struct inode *, struct writeback_control *);
 extern int  ext4_setattr(struct dentry *, struct iattr *);
 extern int  ext4_getattr(struct vfsmount *mnt, struct dentry *dentry,
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 59983b2..437622c 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -4104,6 +4104,16 @@ bad_inode:
 	return ERR_PTR(ret);
 }
 
+struct inode *ext4_iget_normal(struct super_block *sb, unsigned long ino)
+{
+	struct inode *ret_inode = ext4_iget(sb, ino);
+
+	if (ret_inode && !IS_ERR(ret_inode) &&
+	    ino < EXT4_FIRST_INO(sb) && ino != EXT4_ROOT_INO)
+		make_bad_inode(ret_inode);
+	return ret_inode;
+}
+
 static int ext4_inode_blocks_set(handle_t *handle,
 				struct ext4_inode *raw_inode,
 				struct ext4_inode_info *ei)
diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c
index a2a9d40..7037ecf 100644
--- a/fs/ext4/namei.c
+++ b/fs/ext4/namei.c
@@ -1417,7 +1417,7 @@ static struct dentry *ext4_lookup(struct inode *dir, struct dentry *dentry, unsi
 					 dentry);
 			return ERR_PTR(-EIO);
 		}
-		inode = ext4_iget(dir->i_sb, ino);
+		inode = ext4_iget_normal(dir->i_sb, ino);
 		if (inode == ERR_PTR(-ESTALE)) {
 			EXT4_ERROR_INODE(dir,
 					 "deleted inode referenced: %u",
@@ -1450,7 +1450,7 @@ struct dentry *ext4_get_parent(struct dentry *child)
 		return ERR_PTR(-EIO);
 	}
 
-	return d_obtain_alias(ext4_iget(child->d_inode->i_sb, ino));
+	return d_obtain_alias(ext4_iget_normal(child->d_inode->i_sb, ino));
 }
 
 /*
diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 1070d6e..a0811cc 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -1001,7 +1001,7 @@ static struct inode *ext4_nfs_get_inode(struct super_block *sb,
 	 * Currently we don't know the generation for parent directory, so
 	 * a generation of 0 means "accept any"
 	 */
-	inode = ext4_iget(sb, ino);
+	inode = ext4_iget_normal(sb, ino);
 	if (IS_ERR(inode))
 		return ERR_CAST(inode);
 	if (generation && inode->i_generation != generation) {
-- 
2.1.0