On Wed, Jun 20, 2018 at 05:10:04PM -0700, Kees Cook wrote: > On Wed, Jun 20, 2018 at 4:46 PM, Eric Biggers <ebiggers3@xxxxxxxxx> wrote: > > On Wed, Jun 20, 2018 at 12:04:04PM -0700, Kees Cook wrote: > >> In the quest to remove all stack VLA usage from the kernel[1], this uses > >> the maximum blocksize and adds a sanity check. > >> > >> [1] https://lkml.kernel.org/r/CA+55aFzCG-zNmZwX4A2FQpadafLfEzK6CC=qPXydAacU1RqZWA@xxxxxxxxxxxxxx > >> > >> Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx> > >> --- > >> crypto/xcbc.c | 5 ++++- > >> 1 file changed, 4 insertions(+), 1 deletion(-) > >> > >> diff --git a/crypto/xcbc.c b/crypto/xcbc.c > >> index 25c75af50d3f..016481b1f3ba 100644 > >> --- a/crypto/xcbc.c > >> +++ b/crypto/xcbc.c > >> @@ -65,7 +65,10 @@ static int crypto_xcbc_digest_setkey(struct crypto_shash *parent, > >> int bs = crypto_shash_blocksize(parent); > >> u8 *consts = PTR_ALIGN(&ctx->ctx[0], alignmask + 1); > >> int err = 0; > >> - u8 key1[bs]; > >> + u8 key1[CRYPTO_ALG_MAX_BLOCKSIZE]; > >> + > >> + if (WARN_ON(bs > sizeof(key1))) > >> + return -EINVAL; > > > > Similarly, why not MAX_CIPHER_BLOCKSIZE? > > > > Also, xcbc_create() only allows a 16-byte block size, and you made the API > > enforce the maximum for algorithms anyway. So I think the extra check here > > isn't very worthwhile. > > Is the "parent" argument in crypto_xcbc_digest_setkey() always going > to be the "alg" from xcbc_create()? I couldn't convince myself that > was true. If it is, then yes, this VLA can trivially made to be 16, > but it seemed like they were separate instances... Yes, it's guaranteed to be an instance of "xcbc" which was created by xcbc_create(), so it will have 'cra_blocksize == 16'. So until someone actually tests and enables support in the "xcbc" template for other block sizes (if the XCBC specification allows them), it would also be fine to just '#define XCBC_BLOCK_SIZE 16' at the top of the file and use that everywhere that references the block size. Eric
