[PATCH v5 00/11] crypto: Remove VLA usage

[PATCH v5 00/11] crypto: Remove VLA usage

[Kees Cook]

v5:
- limit AHASH_REQUEST_ON_STACK size only to non-async hash wrapping.
- sanity-check ahash reqsize only when doing shash wrapping.
- remove frame_warn changes in favor of shash conversions and other fixes.
- send ahash to shash conversion patches and other fixes separately.

v4:
- add back *_REQUEST_ON_STACK patches.
- programmatically find stack sizes for *_REQUEST_ON_STACK patches.
- whitelist some code that trips FRAME_WARN on 32-bit builds.
- fix alignment patches.

v3:
- drop *_REQUEST_ON_STACK patches. The rest of this series is pretty
  straight-forward, and I'd like to get them tested in -next while
  we continue to chip away at the *_REQUEST_ON_STACK VLA removal patches
  separately. "Part 2" will continue with those.

v2:
- use 512 instead of PAGE_SIZE / 8 to avoid bloat on large-page archs.
- swtich xcbc to "16" max universally.
- fix typo in bounds check for dm buffer size.
- examine actual reqsizes for skcipher and ahash instead of guessing.
- improve names and comments for alg maxes


This is nearly the last of the VLA removals[1], but it's one of the
largest because crypto gets used in lots of places. After looking
through code, usage, reading the threads Gustavo started, and comparing
the use-cases to the other VLA removals that have landed in the kernel,
I think this series is likely the best way forward to shut the door on
VLAs forever.

As background, the crypto stack usage is for callers to do an immediate
bit of work that doesn't allocate new memory. This means that other VLA
removal techniques (like just using kmalloc) aren't workable, and the
next common technique is needed: examination of maximum stack usage and
the addition of sanity checks. This series does that, and in several
cases, these maximums were already implicit in the code.

This series is intended to land via the crypto tree for 4.19, though
it touches dm and a few other things as well, since there are dependent
patches (new crypto #defines being used, kbuild, etc).

Thanks!

-Kees

[1] https://lkml.kernel.org/r/CA+55aFzCG-zNmZwX4A2FQpadafLfEzK6CC=qPXydAacU1RqZWA@mail.gmail.com

Kees Cook (11):
  crypto: xcbc: Remove VLA usage
  crypto: cbc: Remove VLA usage
  crypto: shash: Remove VLA usage
  dm integrity: Remove VLA usage
  crypto: ahash: Remove VLA usage
  dm verity fec: Remove VLA usage
  crypto alg: Introduce generic max blocksize and alignmask
  crypto: qat: Remove VLA usage
  crypto: shash: Remove VLA usage in unaligned hashing
  crypto: ahash: Remove VLA usage for AHASH_REQUEST_ON_STACK
  crypto: skcipher: Remove VLA usage for SKCIPHER_REQUEST_ON_STACK

 crypto/ahash.c                           |  4 +--
 crypto/algapi.c                          |  7 +++-
 crypto/algif_hash.c                      |  2 +-
 crypto/shash.c                           | 42 +++++++++++++++---------
 crypto/xcbc.c                            |  9 +++--
 drivers/crypto/qat/qat_common/qat_algs.c |  8 +++--
 drivers/md/dm-integrity.c                | 23 +++++++++----
 drivers/md/dm-verity-fec.c               |  5 ++-
 include/crypto/algapi.h                  |  4 ++-
 include/crypto/cbc.h                     |  4 ++-
 include/crypto/hash.h                    | 19 +++++++++--
 include/crypto/internal/skcipher.h       |  1 +
 include/crypto/skcipher.h                |  4 ++-
 include/linux/compiler-gcc.h             |  1 -
 14 files changed, 97 insertions(+), 36 deletions(-)

-- 
2.17.1

[PATCH v5 01/11] crypto: xcbc: Remove VLA usage

[Kees Cook]

In the quest to remove all stack VLA usage from the kernel[1], this uses
the maximum blocksize and adds a sanity check. For xcbc, the blocksize
must always be 16, so use that, since it's already being enforced during
instantiation.

[1] https://lkml.kernel.org/r/CA+55aFzCG-zNmZwX4A2FQpadafLfEzK6CC=qPXydAacU1RqZWA@mail.gmail.com

Signed-off-by: Kees Cook <keescook@chromium.org>
---
 crypto/xcbc.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/crypto/xcbc.c b/crypto/xcbc.c
index 25c75af50d3f..7aa03beed795 100644
--- a/crypto/xcbc.c
+++ b/crypto/xcbc.c
@@ -57,6 +57,8 @@ struct xcbc_desc_ctx {
 	u8 ctx[];
 };
 
+#define XCBC_BLOCKSIZE	16
+
 static int crypto_xcbc_digest_setkey(struct crypto_shash *parent,
 				     const u8 *inkey, unsigned int keylen)
 {
@@ -65,7 +67,10 @@ 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[XCBC_BLOCKSIZE];
+
+	if (WARN_ON(bs > sizeof(key1)))
+		return -EINVAL;
 
 	if ((err = crypto_cipher_setkey(ctx->child, inkey, keylen)))
 		return err;
@@ -212,7 +217,7 @@ static int xcbc_create(struct crypto_template *tmpl, struct rtattr **tb)
 		return PTR_ERR(alg);
 
 	switch(alg->cra_blocksize) {
-	case 16:
+	case XCBC_BLOCKSIZE:
 		break;
 	default:
 		goto out_put_alg;
-- 
2.17.1

Re: [PATCH v5 01/11] crypto: xcbc: Remove VLA usage

[Herbert Xu]

On Mon, Jul 16, 2018 at 09:21:40PM -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. For xcbc, the blocksize
> must always be 16, so use that, since it's already being enforced during
> instantiation.
> 
> [1] https://lkml.kernel.org/r/CA+55aFzCG-zNmZwX4A2FQpadafLfEzK6CC=qPXydAacU1RqZWA@mail.gmail.com
> 
> Signed-off-by: Kees Cook <keescook@chromium.org>
> ---
>  crypto/xcbc.c | 9 +++++++--
>  1 file changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/crypto/xcbc.c b/crypto/xcbc.c
> index 25c75af50d3f..7aa03beed795 100644
> --- a/crypto/xcbc.c
> +++ b/crypto/xcbc.c
> @@ -57,6 +57,8 @@ struct xcbc_desc_ctx {
>  	u8 ctx[];
>  };
>  
> +#define XCBC_BLOCKSIZE	16
> +
>  static int crypto_xcbc_digest_setkey(struct crypto_shash *parent,
>  				     const u8 *inkey, unsigned int keylen)
>  {
> @@ -65,7 +67,10 @@ 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[XCBC_BLOCKSIZE];
> +
> +	if (WARN_ON(bs > sizeof(key1)))
> +		return -EINVAL;

Please remove this.  You already checked it in xcbc_create.

In fact, you should just make bs XCBC_BLOCKSIZE unconditinoally
in this function.

Cheers,
-- 
Email: Herbert Xu <herbert@gondor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt

[PATCH v5 02/11] crypto: cbc: Remove VLA usage

[Kees Cook]

In the quest to remove all stack VLA usage from the kernel[1], this
uses the upper bounds on blocksize. Since this is always a cipher
blocksize, use the existing cipher max blocksize.

[1] https://lkml.kernel.org/r/CA+55aFzCG-zNmZwX4A2FQpadafLfEzK6CC=qPXydAacU1RqZWA@mail.gmail.com

Signed-off-by: Kees Cook <keescook@chromium.org>
---
 include/crypto/cbc.h | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/include/crypto/cbc.h b/include/crypto/cbc.h
index f5b8bfc22e6d..47db0aac2ab9 100644
--- a/include/crypto/cbc.h
+++ b/include/crypto/cbc.h
@@ -113,7 +113,9 @@ static inline int crypto_cbc_decrypt_inplace(
 	unsigned int bsize = crypto_skcipher_blocksize(tfm);
 	unsigned int nbytes = walk->nbytes;
 	u8 *src = walk->src.virt.addr;
-	u8 last_iv[bsize];
+	u8 last_iv[MAX_CIPHER_BLOCKSIZE];
+
+	BUG_ON(bsize > sizeof(last_iv));
 
 	/* Start of the last block. */
 	src += nbytes - (nbytes & (bsize - 1)) - bsize;
-- 
2.17.1

[PATCH v5 03/11] crypto: shash: Remove VLA usage

[Kees Cook]

In the quest to remove all stack VLA usage from the kernel[1], this
removes the VLAs in SHASH_DESC_ON_STACK (via crypto_shash_descsize())
by using the maximum allowable size (which is now more clearly captured
in a macro). Similar limits are turned into macros as well.

A review of existing sizes shows that SHA512_DIGEST_SIZE (64) is the
largest digest size and that sizeof(struct sha3_state) (360) is the
largest descriptor size. The corresponding maximums are reduced.

[1] https://lkml.kernel.org/r/CA+55aFzCG-zNmZwX4A2FQpadafLfEzK6CC=qPXydAacU1RqZWA@mail.gmail.com

Signed-off-by: Kees Cook <keescook@chromium.org>
---
 crypto/shash.c        | 6 +++---
 include/crypto/hash.h | 6 +++++-
 2 files changed, 8 insertions(+), 4 deletions(-)

diff --git a/crypto/shash.c b/crypto/shash.c
index 5d732c6bb4b2..ab6902c6dae7 100644
--- a/crypto/shash.c
+++ b/crypto/shash.c
@@ -458,9 +458,9 @@ static int shash_prepare_alg(struct shash_alg *alg)
 {
 	struct crypto_alg *base = &alg->base;
 
-	if (alg->digestsize > PAGE_SIZE / 8 ||
-	    alg->descsize > PAGE_SIZE / 8 ||
-	    alg->statesize > PAGE_SIZE / 8)
+	if (alg->digestsize > SHASH_MAX_DIGESTSIZE ||
+	    alg->descsize > SHASH_MAX_DESCSIZE ||
+	    alg->statesize > SHASH_MAX_STATESIZE)
 		return -EINVAL;
 
 	base->cra_type = &crypto_shash_type;
diff --git a/include/crypto/hash.h b/include/crypto/hash.h
index 76e432cab75d..ae14cc0e0cdb 100644
--- a/include/crypto/hash.h
+++ b/include/crypto/hash.h
@@ -151,9 +151,13 @@ struct shash_desc {
 	void *__ctx[] CRYPTO_MINALIGN_ATTR;
 };
 
+#define SHASH_MAX_DIGESTSIZE     64
+#define SHASH_MAX_DESCSIZE      360
+#define SHASH_MAX_STATESIZE     512
+
 #define SHASH_DESC_ON_STACK(shash, ctx)				  \
 	char __##shash##_desc[sizeof(struct shash_desc) +	  \
-		crypto_shash_descsize(ctx)] CRYPTO_MINALIGN_ATTR; \
+		SHASH_MAX_DESCSIZE] CRYPTO_MINALIGN_ATTR; \
 	struct shash_desc *shash = (struct shash_desc *)__##shash##_desc
 
 /**
-- 
2.17.1

[PATCH v5 04/11] dm integrity: Remove VLA usage

[Kees Cook]

In the quest to remove all stack VLA usage from the kernel[1], this uses
the new SHASH_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 +++++++++++++++++------
 1 file changed, 17 insertions(+), 6 deletions(-)

diff --git a/drivers/md/dm-integrity.c b/drivers/md/dm-integrity.c
index 86438b2f10dd..85e8ce1625a2 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[SHASH_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[SHASH_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;
@@ -1466,7 +1477,7 @@ static bool __journal_read_write(struct dm_integrity_io *dio, struct bio *bio,
 				} while (++s < ic->sectors_per_block);
 #ifdef INTERNAL_VERIFY
 				if (ic->internal_hash) {
-					char checksums_onstack[max(crypto_shash_digestsize(ic->internal_hash), ic->tag_size)];
+					char checksums_onstack[max(SHASH_MAX_DIGESTSIZE, MAX_TAG_SIZE)];
 
 					integrity_sector_checksum(ic, logical_sector, mem + bv.bv_offset, checksums_onstack);
 					if (unlikely(memcmp(checksums_onstack, journal_entry_tag(ic, je), ic->tag_size))) {
@@ -1516,7 +1527,7 @@ static bool __journal_read_write(struct dm_integrity_io *dio, struct bio *bio,
 				if (ic->internal_hash) {
 					unsigned digest_size = crypto_shash_digestsize(ic->internal_hash);
 					if (unlikely(digest_size > ic->tag_size)) {
-						char checksums_onstack[digest_size];
+						char checksums_onstack[SHASH_MAX_DIGESTSIZE];
 						integrity_sector_checksum(ic, logical_sector, (char *)js, checksums_onstack);
 						memcpy(journal_entry_tag(ic, je), checksums_onstack, ic->tag_size);
 					} else
@@ -1937,7 +1948,7 @@ static void do_journal_write(struct dm_integrity_c *ic, unsigned write_start,
 				    unlikely(from_replay) &&
 #endif
 				    ic->internal_hash) {
-					char test_tag[max(crypto_shash_digestsize(ic->internal_hash), ic->tag_size)];
+					char test_tag[max_t(size_t, SHASH_MAX_DIGESTSIZE, MAX_TAG_SIZE)];
 
 					integrity_sector_checksum(ic, sec + ((l - j) << ic->sb->log2_sectors_per_block),
 								  (char *)access_journal_data(ic, i, l), test_tag);
-- 
2.17.1

[PATCH v5 05/11] crypto: ahash: Remove VLA usage

[Kees Cook]

In the quest to remove all stack VLA usage from the kernel[1], this
introduces max size macros for ahash, as already done for shash, and
adjust the crypto user to max state size.

[1] https://lkml.kernel.org/r/CA+55aFzCG-zNmZwX4A2FQpadafLfEzK6CC=qPXydAacU1RqZWA@mail.gmail.com

Signed-off-by: Kees Cook <keescook@chromium.org>
---
 crypto/ahash.c        | 4 ++--
 crypto/algif_hash.c   | 2 +-
 include/crypto/hash.h | 3 +++
 3 files changed, 6 insertions(+), 3 deletions(-)

diff --git a/crypto/ahash.c b/crypto/ahash.c
index a64c143165b1..6435bdbe42fd 100644
--- a/crypto/ahash.c
+++ b/crypto/ahash.c
@@ -550,8 +550,8 @@ static int ahash_prepare_alg(struct ahash_alg *alg)
 {
 	struct crypto_alg *base = &alg->halg.base;
 
-	if (alg->halg.digestsize > PAGE_SIZE / 8 ||
-	    alg->halg.statesize > PAGE_SIZE / 8 ||
+	if (alg->halg.digestsize > AHASH_MAX_DIGESTSIZE ||
+	    alg->halg.statesize > AHASH_MAX_STATESIZE ||
 	    alg->halg.statesize == 0)
 		return -EINVAL;
 
diff --git a/crypto/algif_hash.c b/crypto/algif_hash.c
index bfcf595fd8f9..8974ee8ebead 100644
--- a/crypto/algif_hash.c
+++ b/crypto/algif_hash.c
@@ -239,7 +239,7 @@ static int hash_accept(struct socket *sock, struct socket *newsock, int flags,
 	struct alg_sock *ask = alg_sk(sk);
 	struct hash_ctx *ctx = ask->private;
 	struct ahash_request *req = &ctx->req;
-	char state[crypto_ahash_statesize(crypto_ahash_reqtfm(req)) ? : 1];
+	char state[AHASH_MAX_STATESIZE];
 	struct sock *sk2;
 	struct alg_sock *ask2;
 	struct hash_ctx *ctx2;
diff --git a/include/crypto/hash.h b/include/crypto/hash.h
index ae14cc0e0cdb..4fcd0e2368cd 100644
--- a/include/crypto/hash.h
+++ b/include/crypto/hash.h
@@ -64,6 +64,9 @@ struct ahash_request {
 	void *__ctx[] CRYPTO_MINALIGN_ATTR;
 };
 
+#define AHASH_MAX_DIGESTSIZE	512
+#define AHASH_MAX_STATESIZE	512
+
 #define AHASH_REQUEST_ON_STACK(name, ahash) \
 	char __##name##_desc[sizeof(struct ahash_request) + \
 		crypto_ahash_reqsize(ahash)] CRYPTO_MINALIGN_ATTR; \
-- 
2.17.1

Re: [dm-devel] [PATCH v5 05/11] crypto: ahash: Remove VLA usage

[Eric Biggers]

On Mon, Jul 16, 2018 at 09:21:44PM -0700, Kees Cook wrote:
> In the quest to remove all stack VLA usage from the kernel[1], this
> introduces max size macros for ahash, as already done for shash, and
> adjust the crypto user to max state size.
> 
> [1] https://lkml.kernel.org/r/CA+55aFzCG-zNmZwX4A2FQpadafLfEzK6CC=qPXydAacU1RqZWA@mail.gmail.com
> 
> Signed-off-by: Kees Cook <keescook@chromium.org>
> ---
>  crypto/ahash.c        | 4 ++--
>  crypto/algif_hash.c   | 2 +-
>  include/crypto/hash.h | 3 +++
>  3 files changed, 6 insertions(+), 3 deletions(-)
> 
> diff --git a/crypto/ahash.c b/crypto/ahash.c
> index a64c143165b1..6435bdbe42fd 100644
> --- a/crypto/ahash.c
> +++ b/crypto/ahash.c
> @@ -550,8 +550,8 @@ static int ahash_prepare_alg(struct ahash_alg *alg)
>  {
>  	struct crypto_alg *base = &alg->halg.base;
>  
> -	if (alg->halg.digestsize > PAGE_SIZE / 8 ||
> -	    alg->halg.statesize > PAGE_SIZE / 8 ||
> +	if (alg->halg.digestsize > AHASH_MAX_DIGESTSIZE ||
> +	    alg->halg.statesize > AHASH_MAX_STATESIZE ||
>  	    alg->halg.statesize == 0)
>  		return -EINVAL;
>  
> diff --git a/crypto/algif_hash.c b/crypto/algif_hash.c
> index bfcf595fd8f9..8974ee8ebead 100644
> --- a/crypto/algif_hash.c
> +++ b/crypto/algif_hash.c
> @@ -239,7 +239,7 @@ static int hash_accept(struct socket *sock, struct socket *newsock, int flags,
>  	struct alg_sock *ask = alg_sk(sk);
>  	struct hash_ctx *ctx = ask->private;
>  	struct ahash_request *req = &ctx->req;
> -	char state[crypto_ahash_statesize(crypto_ahash_reqtfm(req)) ? : 1];
> +	char state[AHASH_MAX_STATESIZE];
>  	struct sock *sk2;
>  	struct alg_sock *ask2;
>  	struct hash_ctx *ctx2;
> diff --git a/include/crypto/hash.h b/include/crypto/hash.h
> index ae14cc0e0cdb..4fcd0e2368cd 100644
> --- a/include/crypto/hash.h
> +++ b/include/crypto/hash.h
> @@ -64,6 +64,9 @@ struct ahash_request {
>  	void *__ctx[] CRYPTO_MINALIGN_ATTR;
>  };
>  
> +#define AHASH_MAX_DIGESTSIZE	512
> +#define AHASH_MAX_STATESIZE	512
> +

Why is AHASH_MAX_DIGESTSIZE (512) so much larger than SHASH_MAX_DIGESTSIZE (64)?
I would have expected them to be the same.

- Eric

Re: [dm-devel] [PATCH v5 05/11] crypto: ahash: Remove VLA usage

[Kees Cook]

On Tue, Jul 17, 2018 at 9:39 AM, Eric Biggers <ebiggers3@gmail.com> wrote:
> On Mon, Jul 16, 2018 at 09:21:44PM -0700, Kees Cook wrote:
>> In the quest to remove all stack VLA usage from the kernel[1], this
>> introduces max size macros for ahash, as already done for shash, and
>> adjust the crypto user to max state size.
>>
>> [1] https://lkml.kernel.org/r/CA+55aFzCG-zNmZwX4A2FQpadafLfEzK6CC=qPXydAacU1RqZWA@mail.gmail.com
>>
>> Signed-off-by: Kees Cook <keescook@chromium.org>
>> ---
>>  crypto/ahash.c        | 4 ++--
>>  crypto/algif_hash.c   | 2 +-
>>  include/crypto/hash.h | 3 +++
>>  3 files changed, 6 insertions(+), 3 deletions(-)
>>
>> diff --git a/crypto/ahash.c b/crypto/ahash.c
>> index a64c143165b1..6435bdbe42fd 100644
>> --- a/crypto/ahash.c
>> +++ b/crypto/ahash.c
>> @@ -550,8 +550,8 @@ static int ahash_prepare_alg(struct ahash_alg *alg)
>>  {
>>       struct crypto_alg *base = &alg->halg.base;
>>
>> -     if (alg->halg.digestsize > PAGE_SIZE / 8 ||
>> -         alg->halg.statesize > PAGE_SIZE / 8 ||
>> +     if (alg->halg.digestsize > AHASH_MAX_DIGESTSIZE ||
>> +         alg->halg.statesize > AHASH_MAX_STATESIZE ||
>>           alg->halg.statesize == 0)
>>               return -EINVAL;
>>
>> diff --git a/crypto/algif_hash.c b/crypto/algif_hash.c
>> index bfcf595fd8f9..8974ee8ebead 100644
>> --- a/crypto/algif_hash.c
>> +++ b/crypto/algif_hash.c
>> @@ -239,7 +239,7 @@ static int hash_accept(struct socket *sock, struct socket *newsock, int flags,
>>       struct alg_sock *ask = alg_sk(sk);
>>       struct hash_ctx *ctx = ask->private;
>>       struct ahash_request *req = &ctx->req;
>> -     char state[crypto_ahash_statesize(crypto_ahash_reqtfm(req)) ? : 1];
>> +     char state[AHASH_MAX_STATESIZE];
>>       struct sock *sk2;
>>       struct alg_sock *ask2;
>>       struct hash_ctx *ctx2;
>> diff --git a/include/crypto/hash.h b/include/crypto/hash.h
>> index ae14cc0e0cdb..4fcd0e2368cd 100644
>> --- a/include/crypto/hash.h
>> +++ b/include/crypto/hash.h
>> @@ -64,6 +64,9 @@ struct ahash_request {
>>       void *__ctx[] CRYPTO_MINALIGN_ATTR;
>>  };
>>
>> +#define AHASH_MAX_DIGESTSIZE 512
>> +#define AHASH_MAX_STATESIZE  512
>> +
>
> Why is AHASH_MAX_DIGESTSIZE (512) so much larger than SHASH_MAX_DIGESTSIZE (64)?
> I would have expected them to be the same.

This was a direct replacement of the PAGE_SIZE / 8 original limit.
This this didn't trip any frame size warnings, it seemed like we
didn't need to do the more narrow limitations done elsewhere.

I am, of course, happy to do a manual review and find a lower
alternative if that's desired.

-Kees

-- 
Kees Cook
Pixel Security

Re: [dm-devel] [PATCH v5 05/11] crypto: ahash: Remove VLA usage

[Eric Biggers]

On Tue, Jul 17, 2018 at 01:07:50PM -0700, Kees Cook wrote:
> On Tue, Jul 17, 2018 at 9:39 AM, Eric Biggers <ebiggers3@gmail.com> wrote:
> > On Mon, Jul 16, 2018 at 09:21:44PM -0700, Kees Cook wrote:
> >> In the quest to remove all stack VLA usage from the kernel[1], this
> >> introduces max size macros for ahash, as already done for shash, and
> >> adjust the crypto user to max state size.
> >>
> >> [1] https://lkml.kernel.org/r/CA+55aFzCG-zNmZwX4A2FQpadafLfEzK6CC=qPXydAacU1RqZWA@mail.gmail.com
> >>
> >> Signed-off-by: Kees Cook <keescook@chromium.org>
> >> ---
> >>  crypto/ahash.c        | 4 ++--
> >>  crypto/algif_hash.c   | 2 +-
> >>  include/crypto/hash.h | 3 +++
> >>  3 files changed, 6 insertions(+), 3 deletions(-)
> >>
> >> diff --git a/crypto/ahash.c b/crypto/ahash.c
> >> index a64c143165b1..6435bdbe42fd 100644
> >> --- a/crypto/ahash.c
> >> +++ b/crypto/ahash.c
> >> @@ -550,8 +550,8 @@ static int ahash_prepare_alg(struct ahash_alg *alg)
> >>  {
> >>       struct crypto_alg *base = &alg->halg.base;
> >>
> >> -     if (alg->halg.digestsize > PAGE_SIZE / 8 ||
> >> -         alg->halg.statesize > PAGE_SIZE / 8 ||
> >> +     if (alg->halg.digestsize > AHASH_MAX_DIGESTSIZE ||
> >> +         alg->halg.statesize > AHASH_MAX_STATESIZE ||
> >>           alg->halg.statesize == 0)
> >>               return -EINVAL;
> >>
> >> diff --git a/crypto/algif_hash.c b/crypto/algif_hash.c
> >> index bfcf595fd8f9..8974ee8ebead 100644
> >> --- a/crypto/algif_hash.c
> >> +++ b/crypto/algif_hash.c
> >> @@ -239,7 +239,7 @@ static int hash_accept(struct socket *sock, struct socket *newsock, int flags,
> >>       struct alg_sock *ask = alg_sk(sk);
> >>       struct hash_ctx *ctx = ask->private;
> >>       struct ahash_request *req = &ctx->req;
> >> -     char state[crypto_ahash_statesize(crypto_ahash_reqtfm(req)) ? : 1];
> >> +     char state[AHASH_MAX_STATESIZE];
> >>       struct sock *sk2;
> >>       struct alg_sock *ask2;
> >>       struct hash_ctx *ctx2;
> >> diff --git a/include/crypto/hash.h b/include/crypto/hash.h
> >> index ae14cc0e0cdb..4fcd0e2368cd 100644
> >> --- a/include/crypto/hash.h
> >> +++ b/include/crypto/hash.h
> >> @@ -64,6 +64,9 @@ struct ahash_request {
> >>       void *__ctx[] CRYPTO_MINALIGN_ATTR;
> >>  };
> >>
> >> +#define AHASH_MAX_DIGESTSIZE 512
> >> +#define AHASH_MAX_STATESIZE  512
> >> +
> >
> > Why is AHASH_MAX_DIGESTSIZE (512) so much larger than SHASH_MAX_DIGESTSIZE (64)?
> > I would have expected them to be the same.
> 
> This was a direct replacement of the PAGE_SIZE / 8 original limit.
> This this didn't trip any frame size warnings, it seemed like we
> didn't need to do the more narrow limitations done elsewhere.
> 
> I am, of course, happy to do a manual review and find a lower
> alternative if that's desired.
> 

I just don't see why ahash algorithms would need such a huge maximum digest
size.  Don't the 'ahash' algorithms all have 'shash' equivalents too?  Is there
actually any hash algorithm, either shash or ahash, in the Linux kernel that has
a digest size greater than 64 bytes (512 bits)?  Note that for a real
cryptographic hash there isn't really any need for a digest size larger than
that, since that already gives you 256-bit collision resistance; that's why
SHA-2 and SHA-3 max out at that size.

- Eric

Re: [dm-devel] [PATCH v5 05/11] crypto: ahash: Remove VLA usage

[Kees Cook]

On Tue, Jul 17, 2018 at 4:12 PM, Eric Biggers <ebiggers3@gmail.com> wrote:
> I just don't see why ahash algorithms would need such a huge maximum digest
> size.  Don't the 'ahash' algorithms all have 'shash' equivalents too?  Is there
> actually any hash algorithm, either shash or ahash, in the Linux kernel that has
> a digest size greater than 64 bytes (512 bits)?  Note that for a real
> cryptographic hash there isn't really any need for a digest size larger than
> that, since that already gives you 256-bit collision resistance; that's why
> SHA-2 and SHA-3 max out at that size.

Yup, it certainly looks that way on investigation. I'll adjust both
ahash and shash to use the same #define.

-Kees

-- 
Kees Cook
Pixel Security

[PATCH v5 06/11] dm verity fec: Remove VLA usage

[Kees Cook]

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@mail.gmail.com

Signed-off-by: Kees Cook <keescook@chromium.org>
---
 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..fe5cfd1a5fa5 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;
+
 	/*
 	 * read each of the rsn data blocks that are part of the RS block, and
 	 * interleave contents to available bufs
-- 
2.17.1

[PATCH v5 07/11] crypto alg: Introduce generic max blocksize and alignmask

[Kees Cook]

In the quest to remove all stack VLA usage from the kernel[1], this
exposes a new general upper bound on crypto blocksize and alignmask
(higher than for the existing cipher limits) for VLA removal,
and introduces new checks.

At present, the highest cra_alignmask in the kernel is 63. The highest
cra_blocksize is 144 (SHA3_224_BLOCK_SIZE, 18 8-byte words). For the
new blocksize limit, I went with 160 (20 8-byte words).

[1] https://lkml.kernel.org/r/CA+55aFzCG-zNmZwX4A2FQpadafLfEzK6CC=qPXydAacU1RqZWA@mail.gmail.com

Signed-off-by: Kees Cook <keescook@chromium.org>
---
 crypto/algapi.c         | 7 ++++++-
 include/crypto/algapi.h | 4 +++-
 2 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/crypto/algapi.c b/crypto/algapi.c
index c0755cf4f53f..496fc51bf215 100644
--- a/crypto/algapi.c
+++ b/crypto/algapi.c
@@ -57,9 +57,14 @@ static int crypto_check_alg(struct crypto_alg *alg)
 	if (alg->cra_alignmask & (alg->cra_alignmask + 1))
 		return -EINVAL;
 
-	if (alg->cra_blocksize > PAGE_SIZE / 8)
+	/* General maximums for all algs. */
+	if (alg->cra_alignmask > MAX_ALGAPI_ALIGNMASK)
 		return -EINVAL;
 
+	if (alg->cra_blocksize > MAX_ALGAPI_BLOCKSIZE)
+		return -EINVAL;
+
+	/* Lower maximums for specific alg types. */
 	if (!alg->cra_type && (alg->cra_flags & CRYPTO_ALG_TYPE_MASK) ==
 			       CRYPTO_ALG_TYPE_CIPHER) {
 		if (alg->cra_alignmask > MAX_CIPHER_ALIGNMASK)
diff --git a/include/crypto/algapi.h b/include/crypto/algapi.h
index bd5e8ccf1687..21371ac8f355 100644
--- a/include/crypto/algapi.h
+++ b/include/crypto/algapi.h
@@ -20,8 +20,10 @@
 /*
  * Maximum values for blocksize and alignmask, used to allocate
  * static buffers that are big enough for any combination of
- * ciphers and architectures.
+ * algs and architectures. Ciphers have a lower maximum size.
  */
+#define MAX_ALGAPI_BLOCKSIZE		160
+#define MAX_ALGAPI_ALIGNMASK		63
 #define MAX_CIPHER_BLOCKSIZE		16
 #define MAX_CIPHER_ALIGNMASK		15
 
-- 
2.17.1

[PATCH v5 08/11] crypto: qat: Remove VLA usage

[Kees Cook]

In the quest to remove all stack VLA usage from the kernel[1], this uses
the new upper bound for the stack buffer. Also adds a sanity check.

[1] https://lkml.kernel.org/r/CA+55aFzCG-zNmZwX4A2FQpadafLfEzK6CC=qPXydAacU1RqZWA@mail.gmail.com

Signed-off-by: Kees Cook <keescook@chromium.org>
---
 drivers/crypto/qat/qat_common/qat_algs.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/drivers/crypto/qat/qat_common/qat_algs.c b/drivers/crypto/qat/qat_common/qat_algs.c
index 1138e41d6805..a28edf7b792f 100644
--- a/drivers/crypto/qat/qat_common/qat_algs.c
+++ b/drivers/crypto/qat/qat_common/qat_algs.c
@@ -153,8 +153,8 @@ static int qat_alg_do_precomputes(struct icp_qat_hw_auth_algo_blk *hash,
 	struct sha512_state sha512;
 	int block_size = crypto_shash_blocksize(ctx->hash_tfm);
 	int digest_size = crypto_shash_digestsize(ctx->hash_tfm);
-	char ipad[block_size];
-	char opad[block_size];
+	char ipad[MAX_ALGAPI_BLOCKSIZE];
+	char opad[MAX_ALGAPI_BLOCKSIZE];
 	__be32 *hash_state_out;
 	__be64 *hash512_state_out;
 	int i, offset;
@@ -164,6 +164,10 @@ static int qat_alg_do_precomputes(struct icp_qat_hw_auth_algo_blk *hash,
 	shash->tfm = ctx->hash_tfm;
 	shash->flags = 0x0;
 
+	if (WARN_ON(block_size > sizeof(ipad) ||
+		    sizeof(ipad) != sizeof(opad)))
+		return -EINVAL;
+
 	if (auth_keylen > block_size) {
 		int ret = crypto_shash_digest(shash, auth_key,
 					      auth_keylen, ipad);
-- 
2.17.1

[PATCH v5 09/11] crypto: shash: Remove VLA usage in unaligned hashing

[Kees Cook]

In the quest to remove all stack VLA usage from the kernel[1], this uses
the newly defined max alignment to perform unaligned hashing to avoid
VLAs, and drops the helper function while adding sanity checks on the
resulting buffer sizes. Additionally, the __aligned_largest macro is
removed since this helper was the only user.

[1] https://lkml.kernel.org/r/CA+55aFzCG-zNmZwX4A2FQpadafLfEzK6CC=qPXydAacU1RqZWA@mail.gmail.com

Signed-off-by: Kees Cook <keescook@chromium.org>
---
 crypto/shash.c               | 27 ++++++++++++++++-----------
 include/linux/compiler-gcc.h |  1 -
 2 files changed, 16 insertions(+), 12 deletions(-)

diff --git a/crypto/shash.c b/crypto/shash.c
index ab6902c6dae7..8d4746b14dd5 100644
--- a/crypto/shash.c
+++ b/crypto/shash.c
@@ -73,13 +73,6 @@ int crypto_shash_setkey(struct crypto_shash *tfm, const u8 *key,
 }
 EXPORT_SYMBOL_GPL(crypto_shash_setkey);
 
-static inline unsigned int shash_align_buffer_size(unsigned len,
-						   unsigned long mask)
-{
-	typedef u8 __aligned_largest u8_aligned;
-	return len + (mask & ~(__alignof__(u8_aligned) - 1));
-}
-
 static int shash_update_unaligned(struct shash_desc *desc, const u8 *data,
 				  unsigned int len)
 {
@@ -88,11 +81,17 @@ static int shash_update_unaligned(struct shash_desc *desc, const u8 *data,
 	unsigned long alignmask = crypto_shash_alignmask(tfm);
 	unsigned int unaligned_len = alignmask + 1 -
 				     ((unsigned long)data & alignmask);
-	u8 ubuf[shash_align_buffer_size(unaligned_len, alignmask)]
-		__aligned_largest;
+	/*
+	 * We cannot count on __aligned() working for large values:
+	 * https://patchwork.kernel.org/patch/9507697/
+	 */
+	u8 ubuf[MAX_ALGAPI_ALIGNMASK * 2];
 	u8 *buf = PTR_ALIGN(&ubuf[0], alignmask + 1);
 	int err;
 
+	if (WARN_ON(buf + unaligned_len > ubuf + sizeof(ubuf)))
+		return -EINVAL;
+
 	if (unaligned_len > len)
 		unaligned_len = len;
 
@@ -124,11 +123,17 @@ static int shash_final_unaligned(struct shash_desc *desc, u8 *out)
 	unsigned long alignmask = crypto_shash_alignmask(tfm);
 	struct shash_alg *shash = crypto_shash_alg(tfm);
 	unsigned int ds = crypto_shash_digestsize(tfm);
-	u8 ubuf[shash_align_buffer_size(ds, alignmask)]
-		__aligned_largest;
+	/*
+	 * We cannot count on __aligned() working for large values:
+	 * https://patchwork.kernel.org/patch/9507697/
+	 */
+	u8 ubuf[MAX_ALGAPI_ALIGNMASK + SHASH_MAX_DIGESTSIZE];
 	u8 *buf = PTR_ALIGN(&ubuf[0], alignmask + 1);
 	int err;
 
+	if (WARN_ON(buf + ds > ubuf + sizeof(ubuf)))
+		return -EINVAL;
+
 	err = shash->final(desc, buf);
 	if (err)
 		goto out;
diff --git a/include/linux/compiler-gcc.h b/include/linux/compiler-gcc.h
index f1a7492a5cc8..1f1cdef36a82 100644
--- a/include/linux/compiler-gcc.h
+++ b/include/linux/compiler-gcc.h
@@ -125,7 +125,6 @@
  */
 #define __pure			__attribute__((pure))
 #define __aligned(x)		__attribute__((aligned(x)))
-#define __aligned_largest	__attribute__((aligned))
 #define __printf(a, b)		__attribute__((format(printf, a, b)))
 #define __scanf(a, b)		__attribute__((format(scanf, a, b)))
 #define __attribute_const__	__attribute__((__const__))
-- 
2.17.1

[PATCH v5 10/11] crypto: ahash: Remove VLA usage for AHASH_REQUEST_ON_STACK

[Kees Cook]

In the quest to remove all stack VLA usage from the kernel[1], this caps
the ahash request size similar to the other limits and adds a sanity
check at initialization. AHASH_REQUEST_ON_STACK is special, though: it
is only ever used for shash-wrapped ahash, so its size is bounded only
by non-async hashes. A manual inspection of this shows the largest to be:
sizeof(struct shash_desc) + SHASH_MAX_DESCSIZE

[1] https://lkml.kernel.org/r/CA+55aFzCG-zNmZwX4A2FQpadafLfEzK6CC=qPXydAacU1RqZWA@mail.gmail.com

Signed-off-by: Kees Cook <keescook@chromium.org>
---
 crypto/shash.c        |  9 ++++++++-
 include/crypto/hash.h | 10 +++++++++-
 2 files changed, 17 insertions(+), 2 deletions(-)

diff --git a/crypto/shash.c b/crypto/shash.c
index 8d4746b14dd5..e344560458cb 100644
--- a/crypto/shash.c
+++ b/crypto/shash.c
@@ -355,6 +355,7 @@ int crypto_init_shash_ops_async(struct crypto_tfm *tfm)
 	struct crypto_ahash *crt = __crypto_ahash_cast(tfm);
 	struct crypto_shash **ctx = crypto_tfm_ctx(tfm);
 	struct crypto_shash *shash;
+	size_t reqsize;
 
 	if (!crypto_mod_get(calg))
 		return -EAGAIN;
@@ -365,6 +366,12 @@ int crypto_init_shash_ops_async(struct crypto_tfm *tfm)
 		return PTR_ERR(shash);
 	}
 
+	reqsize = sizeof(struct shash_desc) + crypto_shash_descsize(shash);
+	if (WARN_ON(reqsize > AHASH_MAX_REQSIZE)) {
+		crypto_mod_put(calg);
+		return -EINVAL;
+	}
+
 	*ctx = shash;
 	tfm->exit = crypto_exit_shash_ops_async;
 
@@ -383,7 +390,7 @@ int crypto_init_shash_ops_async(struct crypto_tfm *tfm)
 	if (alg->import)
 		crt->import = shash_async_import;
 
-	crt->reqsize = sizeof(struct shash_desc) + crypto_shash_descsize(shash);
+	crt->reqsize = reqsize;
 
 	return 0;
 }
diff --git a/include/crypto/hash.h b/include/crypto/hash.h
index 4fcd0e2368cd..2181fb38eab9 100644
--- a/include/crypto/hash.h
+++ b/include/crypto/hash.h
@@ -67,9 +67,17 @@ struct ahash_request {
 #define AHASH_MAX_DIGESTSIZE	512
 #define AHASH_MAX_STATESIZE	512
 
+/*
+ * HASH_REQUEST_ON_STACK must only be used when wrapping shash (i.e.
+ * allocated with a CRYPTO_ALG_ASYNC mask), and is generally discouraged
+ * (just use shash directly). This is really only ever needed when using
+ * scatter/gather input sources.
+ */
+#define AHASH_MAX_REQSIZE	(sizeof(struct shash_desc) + \
+				 SHASH_MAX_DESCSIZE)
 #define AHASH_REQUEST_ON_STACK(name, ahash) \
 	char __##name##_desc[sizeof(struct ahash_request) + \
-		crypto_ahash_reqsize(ahash)] CRYPTO_MINALIGN_ATTR; \
+		AHASH_MAX_REQSIZE] CRYPTO_MINALIGN_ATTR; \
 	struct ahash_request *name = (void *)__##name##_desc
 
 /**
-- 
2.17.1

Re: [dm-devel] [PATCH v5 10/11] crypto: ahash: Remove VLA usage for AHASH_REQUEST_ON_STACK

[Eric Biggers]

On Mon, Jul 16, 2018 at 09:21:49PM -0700, Kees Cook wrote:
> In the quest to remove all stack VLA usage from the kernel[1], this caps
> the ahash request size similar to the other limits and adds a sanity
> check at initialization. AHASH_REQUEST_ON_STACK is special, though: it
> is only ever used for shash-wrapped ahash, so its size is bounded only
> by non-async hashes. A manual inspection of this shows the largest to be:
> sizeof(struct shash_desc) + SHASH_MAX_DESCSIZE
> 
> [1] https://lkml.kernel.org/r/CA+55aFzCG-zNmZwX4A2FQpadafLfEzK6CC=qPXydAacU1RqZWA@mail.gmail.com
> 
> Signed-off-by: Kees Cook <keescook@chromium.org>
> ---
>  crypto/shash.c        |  9 ++++++++-
>  include/crypto/hash.h | 10 +++++++++-
>  2 files changed, 17 insertions(+), 2 deletions(-)
> 
> diff --git a/crypto/shash.c b/crypto/shash.c
> index 8d4746b14dd5..e344560458cb 100644
> --- a/crypto/shash.c
> +++ b/crypto/shash.c
> @@ -355,6 +355,7 @@ int crypto_init_shash_ops_async(struct crypto_tfm *tfm)
>  	struct crypto_ahash *crt = __crypto_ahash_cast(tfm);
>  	struct crypto_shash **ctx = crypto_tfm_ctx(tfm);
>  	struct crypto_shash *shash;
> +	size_t reqsize;
>  
>  	if (!crypto_mod_get(calg))
>  		return -EAGAIN;
> @@ -365,6 +366,12 @@ int crypto_init_shash_ops_async(struct crypto_tfm *tfm)
>  		return PTR_ERR(shash);
>  	}
>  
> +	reqsize = sizeof(struct shash_desc) + crypto_shash_descsize(shash);
> +	if (WARN_ON(reqsize > AHASH_MAX_REQSIZE)) {
> +		crypto_mod_put(calg);
> +		return -EINVAL;
> +	}

'crypto_free_shash(shash);' instead of 'crypto_mod_put(calg);'

- Eric

Re: [dm-devel] [PATCH v5 10/11] crypto: ahash: Remove VLA usage for AHASH_REQUEST_ON_STACK

[Kees Cook]

On Tue, Jul 17, 2018 at 9:43 AM, Eric Biggers <ebiggers3@gmail.com> wrote:
> On Mon, Jul 16, 2018 at 09:21:49PM -0700, Kees Cook wrote:
>> +     reqsize = sizeof(struct shash_desc) + crypto_shash_descsize(shash);
>> +     if (WARN_ON(reqsize > AHASH_MAX_REQSIZE)) {
>> +             crypto_mod_put(calg);
>> +             return -EINVAL;
>> +     }
>
> 'crypto_free_shash(shash);' instead of 'crypto_mod_put(calg);'

Oops! Yes, thanks; I have fixed it now in the next version.

-Kees

-- 
Kees Cook
Pixel Security

[PATCH v5 11/11] crypto: skcipher: Remove VLA usage for SKCIPHER_REQUEST_ON_STACK

[Kees Cook]

In the quest to remove all stack VLA usage from the kernel[1], this
caps the skcipher request size similar to other limits and adds a sanity
check at registration. Looking at instrumented tcrypt output, the largest
is for lrw:

	crypt: testing lrw(aes)
	crypto_skcipher_set_reqsize: 8
	crypto_skcipher_set_reqsize: 88
	crypto_skcipher_set_reqsize: 472

[1] https://lkml.kernel.org/r/CA+55aFzCG-zNmZwX4A2FQpadafLfEzK6CC=qPXydAacU1RqZWA@mail.gmail.com

Signed-off-by: Kees Cook <keescook@chromium.org>
---
 include/crypto/internal/skcipher.h | 1 +
 include/crypto/skcipher.h          | 4 +++-
 2 files changed, 4 insertions(+), 1 deletion(-)

diff --git a/include/crypto/internal/skcipher.h b/include/crypto/internal/skcipher.h
index e42f7063f245..5035482cbe68 100644
--- a/include/crypto/internal/skcipher.h
+++ b/include/crypto/internal/skcipher.h
@@ -130,6 +130,7 @@ static inline struct crypto_skcipher *crypto_spawn_skcipher(
 static inline void crypto_skcipher_set_reqsize(
 	struct crypto_skcipher *skcipher, unsigned int reqsize)
 {
+	BUG_ON(reqsize > SKCIPHER_MAX_REQSIZE);
 	skcipher->reqsize = reqsize;
 }
 
diff --git a/include/crypto/skcipher.h b/include/crypto/skcipher.h
index 2f327f090c3e..c48e194438cf 100644
--- a/include/crypto/skcipher.h
+++ b/include/crypto/skcipher.h
@@ -139,9 +139,11 @@ struct skcipher_alg {
 	struct crypto_alg base;
 };
 
+#define SKCIPHER_MAX_REQSIZE	472
+
 #define SKCIPHER_REQUEST_ON_STACK(name, tfm) \
 	char __##name##_desc[sizeof(struct skcipher_request) + \
-		crypto_skcipher_reqsize(tfm)] CRYPTO_MINALIGN_ATTR; \
+		SKCIPHER_MAX_REQSIZE] CRYPTO_MINALIGN_ATTR; \
 	struct skcipher_request *name = (void *)__##name##_desc
 
 /**
-- 
2.17.1