linux-kernel - Re: [PATCH] nilfs2: fix use-after-free bug in nilfs_mdt

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Message-ID: <YvrQ8xO9Lx7rdKq8@ZenIV>
Date:   Tue, 16 Aug 2022 00:04:19 +0100
From:   Al Viro <viro@...iv.linux.org.uk>
To:     Ryusuke Konishi <konishi.ryusuke@...il.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        linux-nilfs <linux-nilfs@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Jiacheng Xu <stitch@....edu.cn>,
        Mudong Liang <mudongliangabcd@...il.com>
Subject: Re: [PATCH] nilfs2: fix use-after-free bug in nilfs_mdt_destroy()

On Tue, Aug 16, 2022 at 05:34:12AM +0900, Ryusuke Konishi wrote:

> Yes, I agree it's better if security_inode_alloc() is moved to the end as
> possible in the sense of avoiding similar issues.
> But, would that vfs change be safe to backport to stable trees?

Yes.

> It looks like the error handling for security_inode_alloc()  is in the
> middle of inode_init_always() for a very long time..

Look at the initializations done after it.  The only thing with effects
outside of inode itself is (since 2010) an increment of nr_inodes.

> If you want to see the impact of the vfs change, I think it's one way
> to apply this one in advance.  Or if you want to fix it in one step,
> I think it's good too.  How do you feel about this ?

IMO that should go into inode_init_always(), with Cc:stable.  If you
(or Dongliang Mu, or anybody else) would post such variant with
reasonable commit message, I'll pick it into vfs.git and feed to Linus
in the next window.  E.g. into #work.inode, with that branch being
made never-rebased, so that you could pull it into your development
branch as soon as it's there...