linux-kernel - Re: [PATCH][next] PCI/P2PDMA: Fix undefined behavior bug in struct pci_p2pdma

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Message-ID: <734c7fdf-4c41-2890-dbe7-ddb23fd6bcc7@embeddedor.com>
Date:   Mon, 2 Oct 2023 20:40:31 +0200
From:   "Gustavo A. R. Silva" <gustavo@...eddedor.com>
To:     Logan Gunthorpe <logang@...tatee.com>,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>
Cc:     linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-hardening@...r.kernel.org
Subject: Re: [PATCH][next] PCI/P2PDMA: Fix undefined behavior bug in struct
 pci_p2pdma_pagemap



On 10/2/23 18:07, Logan Gunthorpe wrote:
> 
> 
> On 2023-10-01 15:08, Gustavo A. R. Silva wrote:
>> `struct dev_pagemap` is a flexible structure, which means that it
>> contains a flexible-array member at the bottom. This could potentially
>> lead to an overwrite of the objects following `pgmap` in `struct
>> pci_p2pdma_pagemap`, when `nr_range > 1`.
>>
>> Fix this by placing the declaration of object `pgmap` at the end of
>> `struct pci_p2pdma_pagemap`.
>>
>> -Wflex-array-member-not-at-end is coming in GCC-14, and we are getting
>> ready to enable it globally.
>>
>> Fixes: 0afea3814358 ("PCI/P2PDMA: Add provider's pci_dev to pci_p2pdma_pagemap struct")
>> Fixes: a6e6fe6549f6 ("PCI/P2PDMA: Introduce private pagemap structure")
>> Cc: stable@...r.kernel.org
>> Signed-off-by: Gustavo A. R. Silva <gustavoars@...nel.org>
> 
> 
> Makes sense to me, thanks.
> 
> Although, I'm not sure the fixes tags are appropriate. The
> flexible-array member was introduced in 5.10 (b7b3c01b19) and both the
> "fixed" commits predate that change by a number of releases.

You're right. I'll remove those tags.

> 
> Also, it's probably worth noting in the commit message that the p2pdma
> code hardcodes nr_ranges to 1 (in pci_p2pdma_add_resource); so there is
> no way to actually hit any bug with the current code.

Yep. I mention that in this part "This could potentially lead to an
overwrite of the objects following `pgmap` in `struct pci_p2pdma_pagemap`,
when `nr_range > 1`."

> 
> I totally agree that the patch should be applied to prevent possible
> bugs being introduced in the future:
> 
> Reviewed-by: Logan Gunthorpe <logang@...tatee.com>

Thanks for the RB and the feedback. :)
--
Gustavo