ext4: disallow ea_inodes with extended attributes

An ea_inode stores the value of an extended attribute; it can not have
extended attributes itself, or this will cause recursive nightmares.
Add a check in ext4_iget() to make sure this is the case.

Cc: [e-mail]
Reported-by: [e-mail]
Signed-off-by: Theodore Ts'o <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Theodore Ts'o <[e-mail]>

fs/ext4/inode.c

···
 	if (flags & EXT4_IGET_EA_INODE) {
 		if (!(EXT4_I(inode)->i_flags & EXT4_EA_INODE_FL))
 			return "missing EA_INODE flag";
+		if (ext4_test_inode_state(inode, EXT4_STATE_XATTR) ||
+		    EXT4_I(inode)->i_file_acl)
+			return "ea_inode with extended attributes";
 	} else {
 		if ((EXT4_I(inode)->i_flags & EXT4_EA_INODE_FL))
 			return "unexpected EA_INODE flag";