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... -Kees -- Kees Cook Pixel Security
