linux-hardening - Re: [scsi] 6aded12b10: kernel_BUG_at

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Date:   Wed, 23 Mar 2022 15:33:30 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Christoph Hellwig <hch@....de>
Cc:     kernel test robot <oliver.sang@...el.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        Bart Van Assche <bvanassche@....org>,
        John Garry <john.garry@...wei.com>,
        LKML <linux-kernel@...r.kernel.org>, lkp@...ts.01.org,
        lkp@...el.com, "Matthew Wilcox (Oracle)" <willy@...radead.org>,
        linux-mm@...ck.org, linux-hardening@...r.kernel.org
Subject: Re: [scsi]  6aded12b10: kernel_BUG_at_mm/usercopy.c

On Wed, Mar 23, 2022 at 04:47:39PM +0100, Christoph Hellwig wrote:
> On Wed, Mar 23, 2022 at 08:40:30AM -0700, Kees Cook wrote:
> > Regardless, I'm concerned that disabling PAGESPAN will just uncover
> > further checks, though. Where is allocation happening? The check is here:
> 
> blk_mq_alloc_rqs, using alloc_pages_node.  This hasn't actually changed
> with this comment.  Just the size of the allocation shrunk, probably
> leading to the span of pages.

Okay, the page allocator _should_ be fine for that. In the mean time,
lkp should probably just disable PAGESPAN.

> > I *think* the allocation is happening in scsi_ioctl_reset()? But that's
> > a plain kmalloc(), so I'm not sure why PAGESPAN would have tripped...
> > are there other allocation paths?
> 
> scsi_ioctl_reset is the odd one out and does also allocate a request,
> but that request is never used for user copies (and that whole hacky
> side path needs to go away, there is a huge series that needs to be
> finished to sort this out).

Gotcha!

-- 
Kees Cook