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Date:   Wed, 23 Mar 2022 16:47:39 +0100
From:   Christoph Hellwig <hch@lst.de>
To:     Kees Cook <keescook@chromium.org>
Cc:     Christoph Hellwig <hch@lst.de>,
        kernel test robot <oliver.sang@intel.com>,
        "Martin K. Petersen" <martin.petersen@oracle.com>,
        Bart Van Assche <bvanassche@acm.org>,
        John Garry <john.garry@huawei.com>,
        LKML <linux-kernel@vger.kernel.org>, lkp@lists.01.org,
        lkp@intel.com, "Matthew Wilcox (Oracle)" <willy@infradead.org>,
        linux-mm@kvack.org, linux-hardening@vger.kernel.org
Subject: Re: [scsi]  6aded12b10: kernel_BUG_at_mm/usercopy.c
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References: <20220320143453.GD6208@xsang-OptiPlex-9020> <20220323071409.GA25480@lst.de> <202203230809.D63BF9511@keescook>
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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.

> 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).