On Wed, Jun 20, 2018 at 7:30 PM, Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx> wrote: > On Wed, Jun 20, 2018 at 12:04:01PM -0700, Kees Cook wrote: >> In the quest to remove all stack VLA usage from the kernel[1], this >> uses the newly defined max digest size macro. Also adds a sanity-check >> at use-time. >> >> [1] https://lkml.kernel.org/r/CA+55aFzCG-zNmZwX4A2FQpadafLfEzK6CC=qPXydAacU1RqZWA@xxxxxxxxxxxxxx >> >> Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx> >> --- >> drivers/md/dm-verity-fec.c | 5 ++++- >> 1 file changed, 4 insertions(+), 1 deletion(-) >> >> diff --git a/drivers/md/dm-verity-fec.c b/drivers/md/dm-verity-fec.c >> index 684af08d0747..0dfcc52835bc 100644 >> --- a/drivers/md/dm-verity-fec.c >> +++ b/drivers/md/dm-verity-fec.c >> @@ -212,12 +212,15 @@ static int fec_read_bufs(struct dm_verity *v, struct dm_verity_io *io, >> struct dm_verity_fec_io *fio = fec_io(io); >> u64 block, ileaved; >> u8 *bbuf, *rs_block; >> - u8 want_digest[v->digest_size]; >> + u8 want_digest[AHASH_MAX_DIGESTSIZE]; >> unsigned n, k; >> >> if (neras) >> *neras = 0; >> >> + if (WARN_ON(v->digest_size < sizeof(want_digest))) >> + return -EINVAL; > > How about verifying digest_size in the ahash API when algorithms > are registered? That happens already in ahash_prepare_alg() (and see the tweak in patch 3 "crypto: ahash: Remove VLA usage"), but I wanted to keep these run-time checks to avoid any problems in the future of things change. As it's marked as "unlikely" internal to WARN_ON, this shouldn't have a performance impact. -Kees -- Kees Cook Pixel Security
