Re: [PATCH] iommu/omap: fix buffer overflow in debugfs

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

Hi Dan,

Thank you for the patch.

On Thu, Aug 04, 2022 at 05:32:39PM +0300, Dan Carpenter wrote:
> There are two issues here:
> 
> 1) The "len" variable needs to be checked before the very first write.
>    Otherwise if omap2_iommu_dump_ctx() with "bytes" less than 32 it is a
>    buffer overflow.
> 2) The snprintf() function returns the number of bytes that *would* have
>    been copied if there were enough space.  But we want to know the
>    number of bytes which were *actually* copied so use scnprintf()
>    instead.
> 
> Fixes: bd4396f09a4a ("iommu/omap: Consolidate OMAP IOMMU modules")
> Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
> ---
>  drivers/iommu/omap-iommu-debug.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/iommu/omap-iommu-debug.c b/drivers/iommu/omap-iommu-debug.c
> index a99afb5d9011..259f65291d90 100644
> --- a/drivers/iommu/omap-iommu-debug.c
> +++ b/drivers/iommu/omap-iommu-debug.c
> @@ -32,12 +32,12 @@ static inline bool is_omap_iommu_detached(struct omap_iommu *obj)
>  		ssize_t bytes;						\
>  		const char *str = "%20s: %08x\n";			\
>  		const int maxcol = 32;					\
> -		bytes = snprintf(p, maxcol, str, __stringify(name),	\
> +		if (len < maxcol)					\
> +			goto out;					\
> +		bytes = scnprintf(p, maxcol, str, __stringify(name),	\
>  				 iommu_read_reg(obj, MMU_##name));	\
>  		p += bytes;						\
>  		len -= bytes;						\
> -		if (len < maxcol)					\
> -			goto out;					\
>  	} while (0)

This could would really benefit from being rewritten using a static
table of register name and offset and a loop that iterates over it.
Still, this is a valid bug fix, so

Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

>  static ssize_t

-- 
Regards,

Laurent Pinchart