Messages in this thread | | | From | Kees Cook <> | Date | Tue, 24 Apr 2018 09:07:16 -0700 | Subject | Re: [PATCH] rave-sp: Remove VLA |
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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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