[CRYPTO] digest: Store temporary digest in tfm

When the final result location is unaligned, we store the digest in a
temporary buffer before copying it to the final location.  Currently
that buffer sits on the stack.  This patch moves it to an area in the
tfm, just like the CBC IV buffer.
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

crypto/digest.c

@@ -66,14 +66,18 @@ static void update(struct crypto_tfm *tfm,
 static void final(struct crypto_tfm *tfm, u8 *out)
 {
 	unsigned long alignmask = crypto_tfm_alg_alignmask(tfm);
+	struct digest_alg *digest = &tfm->__crt_alg->cra_digest;
+
 	if (unlikely((unsigned long)out & alignmask)) {
-		unsigned int size = crypto_tfm_alg_digestsize(tfm);
-		u8 buffer[size + alignmask];
-		u8 *dst = (u8 *)ALIGN((unsigned long)buffer, alignmask + 1);
-		tfm->__crt_alg->cra_digest.dia_final(tfm, dst);
-		memcpy(out, dst, size);
+		unsigned long align = alignmask + 1;
+		unsigned long addr = (unsigned long)crypto_tfm_ctx(tfm);
+		u8 *dst = (u8 *)ALIGN(addr, align) +
+			  ALIGN(tfm->__crt_alg->cra_ctxsize, align);
+
+		digest->dia_final(tfm, dst);
+		memcpy(out, dst, digest->dia_digestsize);
 	} else
-		tfm->__crt_alg->cra_digest.dia_final(tfm, out);
+		digest->dia_final(tfm, out);
 }
 
 static int nosetkey(struct crypto_tfm *tfm, const u8 *key, unsigned int keylen)

crypto/internal.h

@@ -99,7 +99,14 @@ static inline void crypto_exit_proc(void)
 static inline unsigned int crypto_digest_ctxsize(struct crypto_alg *alg,
 						 int flags)
 {
-	return alg->cra_ctxsize;
+	unsigned int len = alg->cra_ctxsize;
+
+	if (alg->cra_alignmask) {
+		len = ALIGN(len, (unsigned long)alg->cra_alignmask + 1);
+		len += alg->cra_digest.dia_digestsize;
+	}
+
+	return len;
 }
 
 static inline unsigned int crypto_cipher_ctxsize(struct crypto_alg *alg,