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SubjectRe: [PATCH] rave-sp: Remove VLA
On Mon, Apr 23, 2018 at 10:43 PM, Lee Jones <lee.jones@linaro.org> wrote:
> 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))

Oh, whoops, no, this should be:

+ if (unlikely(checksum_lengh > sizeof(crc_calculated))) {

(To validate the VLA max size.)

-Kees

--
Kees Cook
Pixel Security

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