Re: [PATCH] sg, bsg: mitigate read/write abuse, block uaccess in release

From: Jann Horn <jannh@google.com>
To: Christoph Hellwig <hch@infradead.org>
Cc: axboe@kernel.dk, Douglas Gilbert <dgilbert@interlog.com>,
	Al Viro <viro@zeniv.linux.org.uk>,
	fujita.tomonori@lab.ntt.co.jp, jejb@linux.vnet.ibm.com,
	martin.petersen@oracle.com, linux-block@vger.kernel.org,
	linux-scsi@vger.kernel.org,
	kernel list <linux-kernel@vger.kernel.org>,
	Kernel Hardening <kernel-hardening@lists.openwall.com>,
	security@kernel.org
Subject: Re: [PATCH] sg, bsg: mitigate read/write abuse, block uaccess in release
Date: Tue, 10 Jul 2018 13:53:02 -0700	[thread overview]
Message-ID: <CAG48ez0ahgHZAEYHt_J_MAanRNX+PXN+2MwtR-VM=gm8Ym30kg@mail.gmail.com> (raw)
In-Reply-To: <20180708145840.GA22949@infradead.org>

On Sun, Jul 8, 2018 at 7:58 AM Christoph Hellwig <hch@infradead.org> wrote:
>
> On Thu, Jun 21, 2018 at 08:07:23AM -0600, Jens Axboe wrote:
> > I'd be fine with that, if we knew that nobody uses it. But that's
> > really hard to figure out. I did see Jann's source code scan, which
> > even if non-exhaustive, still shows at least one user of it.
>
> One is an example, and the other looks very close to an example,
> as far as I can tell it was Nic doing a bsg read/write WIP for a
> tgt module without anyone every picking up on it.  I did add the tgt
> list to Cc and no one seemed to care about the bsg read/write support.
> Adding the tgt list back, but I doubt anyone ever actually used it.
>
> > How about we just make the write interface sync? Then any copy can
> > happen while the we block the task, and the read side is just
> > copying the header info back, or dumping it if the task didn't
> > read it before it went away.
>
> How is that going to work?  As far as I can tell each I/O using
> bsg read/write needs a write and a read, so they need to pair
> and thus can't be a purely sync interface.
>
> It also doesn't help with the issue that bsg_write may possible
> write to user memory, which is highly unusal and asking for security
> issues itself.
>
> Either way, we should probably at very least apply a respun version
> of the patch from Jann to 4.18-rc and -stable while we keep discussing
> this.
>
> Jann, can you respin the bsg patch with the same changes as the now
> included sg one?

With the error messages like in my sg patch or like with Linus'
proposed patch (https://lore.kernel.org/lkml/CA+55aFwg-2GP4ASTdd1pusmZkF7c8AN9febVDCaioDxzYJSLfw@mail.gmail.com/)
applied?