udf: Fix bogus checksum computation in udf_rename()

[ Upstream commit 27ab33854873e6fb958cb074681a0107cc2ecc4c ]

Syzbot reports uninitialized memory access in udf_rename() when updating
checksum of '..' directory entry of a moved directory. This is indeed
true as we pass on-stack diriter.fi to the udf_update_tag() and because
that has only struct fileIdentDesc included in it and not the impUse or
name fields, the checksumming function is going to checksum random stack
contents beyond the end of the structure. This is actually harmless
because the following udf_fiiter_write_fi() will recompute the checksum
from on-disk buffers where everything is properly included. So all that
is needed is just removing the bogus calculation.

Fixes: e9109a92d2a9 ("udf: Convert udf_rename() to new directory iteration code")
Link: https://lore.kernel.org/all/000000000000cf405f060d8f75a9@google.com/T/
Link: https://patch.msgid.link/20240617154201.29512-1-jack@suse.cz
Reported-by: syzbot+d31185aa54170f7fc1f5@syzkaller.appspotmail.com
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Sasha Levin <sashal@kernel.org>

fs/udf/namei.c

@@ -876,8 +876,6 @@ static int udf_rename(struct mnt_idmap *idmap, struct inode *old_dir,
 	if (has_diriter) {
 		diriter.fi.icb.extLocation =
 					cpu_to_lelb(UDF_I(new_dir)->i_location);
-		udf_update_tag((char *)&diriter.fi,
-			       udf_dir_entry_len(&diriter.fi));
 		udf_fiiter_write_fi(&diriter, NULL);
 		udf_fiiter_release(&diriter);
 	}