ext4: Do not try to validate extents on special files

The EXTENTS_FL flag should never be set on special files, but if it
is, don't bother trying to validate that the extents tree is valid,
since only files, directories, and non-fast symlinks will ever have an
extent data structure.  We perhaps should flag the filesystem as being
corrupted if we see a special file (named pipes, device nodes, Unix
domain sockets, etc.) with the EXTENTS_FL flag, but e2fsck doesn't
currently check this case, so we'll just ignore this for now, since
it's harmless.

Without this fix, a special device with the extents flag is flagged as
an error by the kernel, so it is impossible to access or delete the
inode, but e2fsck doesn't see it as a problem, leading to
confused/frustrated users.
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

fs/ext4/inode.c

@@ -4407,6 +4407,7 @@ struct inode *ext4_iget(struct super_block *sb, unsigned long ino)
 			(__u64)(le32_to_cpu(raw_inode->i_version_hi)) << 32;
 	}
 
+	ret = 0;
 	if (ei->i_file_acl &&
 	    ((ei->i_file_acl < 
 	      (le32_to_cpu(EXT4_SB(sb)->s_es->s_first_data_block) +
@@ -4418,6 +4419,9 @@ struct inode *ext4_iget(struct super_block *sb, unsigned long ino)
 		ret = -EIO;
 		goto bad_inode;
 	} else if (ei->i_flags & EXT4_EXTENTS_FL) {
+		if (S_ISREG(inode->i_mode) || S_ISDIR(inode->i_mode) ||
+		    (S_ISLNK(inode->i_mode) &&
+		     !ext4_inode_is_fast_symlink(inode)))
 			/* Validate extent which is part of inode */
 			ret = ext4_ext_check_inode(inode);
  	} else if (S_ISREG(inode->i_mode) || S_ISDIR(inode->i_mode) ||