crypto: shash - Remove VLA usage in unaligned hashing

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

1 files changed, 16 insertions, 11 deletions

diff --git a/crypto/shash.c b/crypto/shash.c
index 86d76b5c626c..d21f04d70dce 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 + HASH_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;