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Message-ID: <e76ff7de-8c42-4393-36e2-b37ffcb58149@deltatee.com> Date: Mon, 2 Oct 2023 12:46:04 -0600 From: Logan Gunthorpe <logang@...tatee.com> To: "Gustavo A. R. Silva" <gustavo@...eddedor.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 2023-10-02 12:40, Gustavo A. R. Silva wrote: > > > 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`." Yes, but the commit message is not clear that nr_range can never be >1 in the code as it currently is. Logan
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