linux-kernel - Re: [PATCH] fs: ocfs2: move_extents.c: Fix to remove null pointer checks that could never happen

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20140529212308.GA16353@redhat.com>
Date:	Thu, 29 May 2014 17:23:08 -0400
From:	Dave Jones <davej@...hat.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Rickard Strandqvist <rickard_strandqvist@...ctrumdigital.se>,
	Mark Fasheh <mfasheh@...e.com>,
	Joel Becker <jlbec@...lplan.org>, ocfs2-devel@....oracle.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] fs: ocfs2: move_extents.c:  Fix to remove null pointer
 checks that could never happen

On Thu, May 29, 2014 at 02:03:37PM -0700, Andrew Morton wrote:
 > On Tue, 27 May 2014 22:23:51 +0200 Rickard Strandqvist <rickard_strandqvist@...ctrumdigital.se> wrote:
 > 
 > > Removal of null pointer checks that could never happen
 > 
 > How do you know it never happens?
 > 
 > > --- a/fs/ocfs2/move_extents.c
 > > +++ b/fs/ocfs2/move_extents.c
 > > @@ -904,9 +904,6 @@ static int ocfs2_move_extents(struct ocfs2_move_extents_context *context)
 > >  	struct buffer_head *di_bh = NULL;
 > >  	struct ocfs2_super *osb = OCFS2_SB(inode->i_sb);
 > >  
 > > -	if (!inode)
 > > -		return -ENOENT;
 > > -
 > 
 > If it's due to assuming that the previous statement would have oopsed
 > then that is mistaken.  Is is sometimes the case that gcc will move the
 > evaluation of inode->i_sb to after the test, so this function can be
 > passed NULL and it will not oops.

'sometimes' ?

You have a lot more faith in gcc than I do. What happens if we decide to
switch to llvm one day ? Can we guarantee every compiler will implement
the same magic ?  This seems fragile as hell to me.

	Dave

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/