linux-kernel - Re: [PATCH] jffs2:freely allocate memory when parameters are invalid

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Message-ID: <20190920124532.GN1131@ZenIV.linux.org.uk>
Date:   Fri, 20 Sep 2019 13:45:32 +0100
From:   Al Viro <viro@...iv.linux.org.uk>
To:     Xiaoming Ni <nixiaoming@...wei.com>
Cc:     dwmw2@...radead.org, dilinger@...ued.net, richard@....at,
        houtao1@...wei.com, bbrezillon@...nel.org, daniel.santos@...ox.com,
        linux-mtd@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] jffs2:freely allocate memory when parameters are invalid

On Fri, Sep 20, 2019 at 08:21:53PM +0800, Xiaoming Ni wrote:
> 
> 
> On 2019/9/20 19:43, Al Viro wrote:
> > On Fri, Sep 20, 2019 at 02:54:38PM +0800, Xiaoming Ni wrote:
> >> Use kzalloc() to allocate memory in jffs2_fill_super().
> >> Freeing memory when jffs2_parse_options() fails will cause
> >> use-after-free and double-free in jffs2_kill_sb()
> > 
> > ... so we are not freeing it there.  What's the problem?
> 
> No code logic issues, no memory leaks
> 
> But there is too much code logic between memory allocation and free,
> which is difficult to understand.

Er?  An instance of jffs2 superblock might have a related object
attached to it; it is created in jffs2 superblock constructor and
freed in destructor.

> The modified code is easier to understand.

You are making the cleanup logics harder to follow.