Re: [PATCH] iommu/dmar: fix buffer overflow during PCI bus notification

[Julia Cartwright <julia@ni.com>]

On Wed, Feb 20, 2019 at 10:46:31AM -0600, Julia Cartwright wrote:
> Commit 57384592c433 ("iommu/vt-d: Store bus information in RMRR PCI
> device path") changed the type of the path data, however, the change in
> path type was not reflected in size calculations.  Update to use the
> correct type and prevent a buffer overflow.
> 
> This bug manifests in systems with deep PCI hierarchies, and can lead to
> an overflow of the static allocated buffer (dmar_pci_notify_info_buf),
> or can lead to overflow of slab-allocated data.
> 
>    BUG: KASAN: global-out-of-bounds in dmar_alloc_pci_notify_info+0x1d5/0x2e0
>    Write of size 1 at addr ffffffff90445d80 by task swapper/0/1
>    CPU: 0 PID: 1 Comm: swapper/0 Tainted: G        W       4.14.87-rt49-02406-gd0a0e96 #1
>    Call Trace:
>     ? dump_stack+0x46/0x59
>     ? print_address_description+0x1df/0x290
[..]
>    The buggy address belongs to the variable:
>     dmar_pci_notify_info_buf+0x40/0x60
> 
> Fixes: 57384592c433 ("iommu/vt-d: Store bus information in RMRR PCI device path")
> Signed-off-by: Julia Cartwright <julia@ni.com>
> ---
>  drivers/iommu/dmar.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/iommu/dmar.c b/drivers/iommu/dmar.c
> index 6b7df25e1488..9c49300e9fb7 100644
> --- a/drivers/iommu/dmar.c
> +++ b/drivers/iommu/dmar.c
> @@ -145,7 +145,7 @@ dmar_alloc_pci_notify_info(struct pci_dev *dev, unsigned long event)
>  		for (tmp = dev; tmp; tmp = tmp->bus->self)
>  			level++;
>  
> -	size = sizeof(*info) + level * sizeof(struct acpi_dmar_pci_path);
> +	size = sizeof(*info) + level * sizeof(info->path[0]);

This is probably a candidate for struct_size() instead, if that's what
is preferred.

   Julia