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

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Message-ID: <29da763d-1570-7197-2d5a-03c5659b8b52@deltatee.com>
Date:   Mon, 2 Oct 2023 10:07:21 -0600
From:   Logan Gunthorpe <logang@...tatee.com>
To:     "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 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.

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.

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>

Logan