linux-kernel - Re: [PATCH] ubifs: Fix a potential space leak problem while linking tmpfile

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Date:   Tue, 7 Jul 2020 14:09:01 +0200 (CEST)
From:   Richard Weinberger <richard@....at>
To:     chengzhihao1 <chengzhihao1@...wei.com>
Cc:     Richard Weinberger <richard.weinberger@...il.com>,
        linux-mtd <linux-mtd@...ts.infradead.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        yi zhang <yi.zhang@...wei.com>
Subject: Re: [PATCH] ubifs: Fix a potential space leak problem while linking
 tmpfile

----- Ursprüngliche Mail -----
> Perhaps I misunderstood what commit 32fe905c17f001 ("ubifs: Fix
> O_TMPFILE corner case in ubifs_link()") wanted to fix.
> I think orphan area is used to remind filesystem don't forget to delete
> inodes (whose nlink is 0) in next unclean rebooting. Generally, the file
> system is not corrupted caused by replaying orphan nodes.
> Ralph reported a filesystem corruption in combination with overlayfs.
> Can you tell me the details about that problem? Thanks.

On my test bed I didn't see a fs corruption, what I saw was a failing orphan
self test while playing with O_TMPFILE and linkat().

When you create a tmpfile it has a link count of 0 and an orphan is
installed. Such that the tmpfile is gone after a reboot but you can
still use it prior to that.
By using linkat() you can raise the link counter to 1 again.
Thus, the orphan needs to be removed.
This is pattern overlayfs uses a lot.

Since UBIFS never supported raising the link counter from 0 to 1
we have many corner cases and fixing all these turned out into a nightmare.
...as you can see from the amount broken patches from me :-(.

Thanks,
//richard