linux-kernel - Re: null-ptr-deref due to "ext4: fix potential race between online resizing and write operations"

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Message-ID: <20200222003354.GB873427@mit.edu>
Date:   Fri, 21 Feb 2020 19:33:54 -0500
From:   "Theodore Y. Ts'o" <tytso@....edu>
To:     "Jitindar SIngh, Suraj" <surajjs@...zon.com>
Cc:     "cai@....pw" <cai@....pw>,
        "adilger.kernel@...ger.ca" <adilger.kernel@...ger.ca>,
        "linux-ext4@...r.kernel.org" <linux-ext4@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "paulmck@...nel.org" <paulmck@...nel.org>
Subject: Re: null-ptr-deref due to "ext4: fix potential race between online
 resizing and write operations"

On Fri, Feb 21, 2020 at 07:58:01PM +0000, Jitindar SIngh, Suraj wrote:
> On Fri, 2020-02-21 at 09:02 -0500, Qian Cai wrote:
> > Reverted the linux-next commit c20bac9bf82c ("ext4: fix potential
> > race between
> > s_flex_groups online resizing and access") fixed the crash below
> > (with line
> > numbers),
> 
> Good catch, this is a bug where the dereference of the array
> s_flex_groups needs to happen after the "if (flex_size > 1)" if
> statement in fs/ext4/ialloc.c:373

Cai, thanks for noting the problem!  Suraj, I've fixed up the patch on
the ext4.git tree.

						- Ted