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SubjectRe: [PATCH v8 5/9] dm: Remove VLA usage from hashes
On Tue, Aug 07 2018 at  5:18pm -0400,
Kees Cook <keescook@chromium.org> wrote:

> In the quest to remove all stack VLA usage from the kernel[1], this uses
> the new HASH_MAX_DIGESTSIZE from the crypto layer to allocate the upper
> bounds on stack usage.
>
> [1] https://lkml.kernel.org/r/CA+55aFzCG-zNmZwX4A2FQpadafLfEzK6CC=qPXydAacU1RqZWA@mail.gmail.com
>
> Signed-off-by: Kees Cook <keescook@chromium.org>
> ---
> drivers/md/dm-integrity.c | 23 +++++++++++++++++------
> drivers/md/dm-verity-fec.c | 5 ++++-
> 2 files changed, 21 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/md/dm-integrity.c b/drivers/md/dm-integrity.c
> index 86438b2f10dd..884edd7cf1d0 100644
> --- a/drivers/md/dm-integrity.c
> +++ b/drivers/md/dm-integrity.c
> @@ -521,7 +521,12 @@ static void section_mac(struct dm_integrity_c *ic, unsigned section, __u8 result
> }
> memset(result + size, 0, JOURNAL_MAC_SIZE - size);
> } else {
> - __u8 digest[size];
> + __u8 digest[HASH_MAX_DIGESTSIZE];
> +
> + if (WARN_ON(size > sizeof(digest))) {
> + dm_integrity_io_error(ic, "digest_size", -EINVAL);
> + goto err;
> + }
> r = crypto_shash_final(desc, digest);
> if (unlikely(r)) {
> dm_integrity_io_error(ic, "crypto_shash_final", r);
> @@ -1244,7 +1249,7 @@ static void integrity_metadata(struct work_struct *w)
> struct bio *bio = dm_bio_from_per_bio_data(dio, sizeof(struct dm_integrity_io));
> char *checksums;
> unsigned extra_space = unlikely(digest_size > ic->tag_size) ? digest_size - ic->tag_size : 0;
> - char checksums_onstack[ic->tag_size + extra_space];
> + char checksums_onstack[HASH_MAX_DIGESTSIZE];
> unsigned sectors_to_process = dio->range.n_sectors;
> sector_t sector = dio->range.logical_sector;
>
> @@ -1253,8 +1258,14 @@ static void integrity_metadata(struct work_struct *w)
>
> checksums = kmalloc((PAGE_SIZE >> SECTOR_SHIFT >> ic->sb->log2_sectors_per_block) * ic->tag_size + extra_space,
> GFP_NOIO | __GFP_NORETRY | __GFP_NOWARN);
> - if (!checksums)
> + if (!checksums) {
> checksums = checksums_onstack;
> + if (WARN_ON(extra_space &&
> + digest_size > sizeof(checksums_onstack))) {
> + r = -EINVAL;
> + goto error;
> + }
> + }
>
> __bio_for_each_segment(bv, bio, iter, dio->orig_bi_iter) {
> unsigned pos;

Given the length of the kmalloc() just prior to this new WARN_ON() line
I'm not seeing why you've elected to split the WARN_ON across multiple
lines.

But that style nit aside:

Acked-by: Mike Snitzer <snitzer@redhat.com>

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