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Re: [PATCH] xfs: fix possible NULL dereference

To: Eric Sandeen <sandeen@xxxxxxxxxxx>, Dave Chinner <david@xxxxxxxxxxxxx>
Subject: Re: [PATCH] xfs: fix possible NULL dereference
From: Ben Myers <bpm@xxxxxxx>
Date: Mon, 21 Oct 2013 18:18:49 -0500
Cc: Alex Elder <elder@xxxxxxxxxx>, open list <linux-kernel@xxxxxxxxxxxxxxx>, XFS FILESYSTEM <xfs@xxxxxxxxxxx>, "Geyslan G. Bem" <geyslan@xxxxxxxxx>, kernel-br@xxxxxxxxxxxxxxxx
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <5265B4D2.3000907@xxxxxxxxxxx>
References: <1382380366-26540-1-git-send-email-geyslan@xxxxxxxxx> <5265956F.4010700@xxxxxxxxxxx> <20131021224459.GE16161@dastard> <5265B4D2.3000907@xxxxxxxxxxx>
User-agent: Mutt/1.5.20 (2009-06-14)
Hey,

On Mon, Oct 21, 2013 at 06:12:18PM -0500, Eric Sandeen wrote:
> On 10/21/13 5:44 PM, Dave Chinner wrote:
> > On Mon, Oct 21, 2013 at 03:58:23PM -0500, Eric Sandeen wrote:
> >> On 10/21/13 1:32 PM, Geyslan G. Bem wrote:
> >>> This patch puts a 'break' in the true branch, avoiding the 
> >>> 'icptr->ic_next'
> >>> dereferencing.
> >>
> >> Reviewed-by: Eric Sandeen <sandeen@xxxxxxxxxx>
> > 
> > Actually, NACK.
> 
> I felt that one coming ;)
> 
> >> Hm, yeah - cmn_err(CE_PANIC, " " ); used to BUG_ON, but the newer
> >> xfs_emerg() doesn't.
> >>
> >> Dave, was that intentional?
> > 
> > Of course it was. ;) xfs_emerg() is only called from the debug code
> > in xlog_verify_iclog(), xlog_verify_tail_lsn and assfail().
> > 
> > In the case of assfail(), it has it's own BUG() call, so it does
> > everything just fine.
> > 
> > In the case of xlog_verify_iclog() when icptr is NULL, it will
> > panic immediately after the message is printed, just like the old
> > code. i.e. this patch isn't fixing anything we need fixed. 
> 
> A BUG() is probably warranted, then.

I tend to agree with Eric on this point.  If we want to crash, I'd rather our
intent be very clear, rather than just see a null ptr deref.  ;)

Regards,
        Ben

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