ext4: filesystems without casefold feature cannot be mounted with siphash

When mounting the ext4 filesystem, if the default hash version is set to
DX_HASH_SIPHASH but the casefold feature is not set, exit the mounting.

Reported-by: syzbot+340581ba9dceb7e06fb3@syzkaller.appspotmail.com
Signed-off-by: Lizhi Xu <lizhi.xu@windriver.com>
Link: https://patch.msgid.link/20240605012335.44086-1-lizhi.xu@windriver.comSigned-off-by: Theodore Ts'o <tytso@mit.edu>

fs/ext4/super.c

@@ -3582,6 +3582,13 @@ int ext4_feature_set_ok(struct super_block *sb, int readonly)
 			 "mounted without CONFIG_UNICODE");
 		return 0;
 	}
+	if (EXT4_SB(sb)->s_es->s_def_hash_version == DX_HASH_SIPHASH &&
+	    !ext4_has_feature_casefold(sb)) {
+		ext4_msg(sb, KERN_ERR,
+			 "Filesystem without casefold feature cannot be "
+			 "mounted with siphash");
+		return 0;
+	}
 
 	if (readonly)
 		return 1;