crypto: api - Introduce generic max blocksize and alignmask

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>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

diff --git a/crypto/algapi.c b/crypto/algapi.c
index c0755cf4f53f8b5eb518cd96d77a70fc3f837367..496fc51bf215c230b201658e7411942822a2b474 100644 (file)
--- 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 bd5e8ccf168790359603347374ff6de1a93de7b0..21371ac8f355d5dddc0e00a4652b573641f4d394 100644 (file)
--- 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