ext3: avoid triggering ext3_error on bad NFS file handle

The inode number out of an NFS file handle gets passed eventually to
ext3_get_inode_block() without any checking.  If ext3_get_inode_block()
allows it to trigger an error, then bad filehandles can have unpleasant
effect - ext3_error() will usually cause a forced read-only remount, or a
panic if `errors=panic' was used.

So remove the call to ext3_error there and put a matching check in
ext3/namei.c where inode numbers are read off storage.

Andrew Morton fixed an off-by-one error.

Dann Frazier ported the patch to 2.6.16.

Signed-off-by: Neil Brown <neilb@suse.de>
Signed-off-by: Adrian Bunk <bunk@stusta.de>

include/linux/ext3_fs.h

@@ -494,6 +494,15 @@ static inline struct ext3_inode_info *EXT3_I(struct inode *inode)
 {
 	return container_of(inode, struct ext3_inode_info, vfs_inode);
 }
+
+static inline int ext3_valid_inum(struct super_block *sb, unsigned long ino)
+{
+	return ino == EXT3_ROOT_INO ||
+		ino == EXT3_JOURNAL_INO ||
+		ino == EXT3_RESIZE_INO ||
+		(ino >= EXT3_FIRST_INO(sb) &&
+		 ino <= le32_to_cpu(EXT3_SB(sb)->s_es->s_inodes_count));
+}
 #else
 /* Assume that user mode programs are passing in an ext3fs superblock, not
  * a kernel struct super_block.  This will allow us to call the feature-test