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SubjectRe: [PATCH] rave-sp: Remove VLA
On Mon, 23 Apr 2018, Kyle Spiers wrote:

> As part of the effort to remove VLAs from the kernel[1], this creates
> constants for the checksum lengths of CCITT and 8B2C and changes
> crc_calculated to be the maximum size of a checksum.
>
> https://lkml.org/lkml/2018/3/7/621
>
> Signed-off-by: Kyle Spiers <ksspiers@google.com>
> ---
> drivers/mfd/rave-sp.c | 11 +++++++++--
> 1 file changed, 9 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/mfd/rave-sp.c b/drivers/mfd/rave-sp.c
> index 5c858e784a89..99fa482419f9 100644
> --- a/drivers/mfd/rave-sp.c
> +++ b/drivers/mfd/rave-sp.c
> @@ -45,7 +45,9 @@
> #define RAVE_SP_DLE 0x10
>
> #define RAVE_SP_MAX_DATA_SIZE 64
> -#define RAVE_SP_CHECKSUM_SIZE 2 /* Worst case scenario on RDU2 */
> +#define RAVE_SP_CHECKSUM_8B2C 1
> +#define RAVE_SP_CHECKSUM_CCITT 2
> +#define RAVE_SP_CHECKSUM_SIZE RAVE_SP_CHECKSUM_CCITT
> /*
> * We don't store STX, ETX and unescaped bytes, so Rx is only
> * DATA + CSUM
> @@ -415,7 +417,12 @@ static void rave_sp_receive_frame(struct rave_sp *sp,
> const size_t payload_length = length - checksum_length;
> const u8 *crc_reported = &data[payload_length];
> struct device *dev = &sp->serdev->dev;
> - u8 crc_calculated[checksum_length];
> + u8 crc_calculated[RAVE_SP_CHECKSUM_SIZE];
> +
> + if (unlikely(length > sizeof(crc_calculated))) {

Forgive me if I have this wrong (it's still very early here), but this
doesn't leave any room for the payload?

<-- length -->
<ck len><- payload length ->
[CK][CK][D][A][T][A] .. [64]

It is my hope that length would always be larger than the size of the
checksum, or else there would never be any data?

Should this not be:

if (unlikely(length > RAVE_SP_MAX_DATA_SIZE))

Nit: Adding the check is also an unrelated change, so would require a
separate patch.

> + dev_warn(dev, "Dropping oversized frame\n");
> + return;
> + }
>
> print_hex_dump(KERN_DEBUG, "rave-sp rx: ", DUMP_PREFIX_NONE,
> 16, 1, data, length, false);

--
Lee Jones [李琼斯]
Linaro Services Technical Lead
Linaro.org │ Open source software for ARM SoCs
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