linux-kernel - Re: [syzbot] KASAN: null-ptr-deref Read in __free

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Date:   Mon, 21 Mar 2022 09:50:05 +0100
From:   "Fabio M. De Francesco" <fmdefrancesco@...il.com>
To:     syzbot <syzbot+d55757faa9b80590767b@...kaller.appspotmail.com>,
        syzkaller-bugs@...glegroups.com
Cc:     dhowells@...hat.com, christophe.jaillet@...adoo.fr,
        linux-kernel@...r.kernel.org, syzkaller-bugs@...glegroups.com,
        David Howells <dhowells@...hat.com>
Subject: Re: [syzbot] KASAN: null-ptr-deref Read in __free_pages

On lunedì 21 marzo 2022 09:24:22 CET David Howells wrote:
> It should be possible to just test for the pointer being NULL in the loop
> before calling __free_pages() since the list was allocated with kcalloc().
> 
> David
> 
> #syz test: git://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs.git 6d39b096627f0a1eb6e14f049d8ae3c93e0290f2
> 
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> 
This way you are doing two test for each iteration of the loop that calls
__free_pages(). One for the index "i" to stay less that an unnecessary 
high limit, the other for pages[i] being NULL.

However, since you are the Maintainer, yours are the rules :)

Regards,

Fabio M. De Francesco