Re: [PATCH] firmware: arm_scmi: Fix possible scmi_linux_errmap buffer overflow

[Cristian Marussi <cristian.marussi@arm.com>]

On Wed, Jul 07, 2021 at 02:50:28PM +0100, Sudeep Holla wrote:
> The scmi_linux_errmap buffer access index is supposed to depend on the
> array size to prevent element out of bounds access. It uses SCMI_ERR_MAX
> to check bounds but that can mismatch with the array size. It also
> changes the success into -EIO though scmi_linux_errmap is never used in
> case of success, it is expected to work for success case too.
> 
> It is slightly confusing code as the negative of the error code
> is used as index to the buffer. Fix it by negating it at the start and
> make it more readable.
> 
> Reported-by: kernel test robot <lkp@intel.com>
> Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
> Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>
> ---
>  drivers/firmware/arm_scmi/driver.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> (Based on https://lore.kernel.org/r/20210707134739.1869481-1-sudeep.holla@arm.com)
> 
> diff --git a/drivers/firmware/arm_scmi/driver.c b/drivers/firmware/arm_scmi/driver.c
> index 66e5e694be7d..2a5c1b3658c4 100644
> --- a/drivers/firmware/arm_scmi/driver.c
> +++ b/drivers/firmware/arm_scmi/driver.c
> @@ -166,8 +166,10 @@ static const int scmi_linux_errmap[] = {
>  
>  static inline int scmi_to_linux_errno(int errno)
>  {
> -	if (errno < SCMI_SUCCESS && errno > SCMI_ERR_MAX)
> -		return scmi_linux_errmap[-errno];
> +	int err_idx = -errno;
> +
> +	if (err_idx >= SCMI_SUCCESS && err_idx < ARRAY_SIZE(scmi_linux_errmap))
> +		return scmi_linux_errmap[err_idx];
>  	return -EIO;
>  }
>  
Hi,

Looks good to me; now SCMI_ERR_MAX is not referenced anymore by anyone
but I suppose is good practice to still keep it as an end-marker for
scmi_error_codes enum.

Reviewed-by: Cristian Marussi <cristian.marussi@arm.com>

Thanks,
Cristian

> -- 
> 2.25.1
> 

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