static int crypto_ccm_auth(struct aead_request *req, struct scatterlist *plain,
			   unsigned int cryptlen)
{
	struct crypto_ccm_req_priv_ctx *pctx = crypto_ccm_reqctx(req);
	struct crypto_aead *aead = crypto_aead_reqtfm(req);
	struct crypto_ccm_ctx *ctx = crypto_aead_ctx(aead);
	AHASH_REQUEST_ON_STACK(ahreq, ctx->mac);
	unsigned int assoclen = req->assoclen;
	struct scatterlist sg[3];
	u8 odata[16];
	u8 idata[16];
	int ilen, err;

	/* format control data for input */
	err = format_input(odata, req, cryptlen);
	if (err)
		goto out;

	sg_init_table(sg, 3);
	sg_set_buf(&sg[0], odata, 16);

	/* format associated data and compute into mac */
	if (assoclen) {
		ilen = format_adata(idata, assoclen);
		sg_set_buf(&sg[1], idata, ilen);
		sg_chain(sg, 3, req->src);
	} else {
		ilen = 0;
		sg_chain(sg, 2, req->src);
	}

	ahash_request_set_tfm(ahreq, ctx->mac);
	ahash_request_set_callback(ahreq, pctx->flags, NULL, NULL);
	ahash_request_set_crypt(ahreq, sg, NULL, assoclen + ilen + 16);
	err = crypto_ahash_init(ahreq);
	if (err)
		goto out;
	err = crypto_ahash_update(ahreq);
	if (err)
		goto out;

	/* we need to pad the MAC input to a round multiple of the block size */
	ilen = 16 - (assoclen + ilen) % 16;
	if (ilen < 16) {
		memset(idata, 0, ilen);
		sg_init_table(sg, 2);
		sg_set_buf(&sg[0], idata, ilen);
		if (plain)
			sg_chain(sg, 2, plain);
		plain = sg;
		cryptlen += ilen;
	}

	ahash_request_set_crypt(ahreq, plain, pctx->odata, cryptlen);
	err = crypto_ahash_finup(ahreq);
out:
	return err;
}
The software performs operations on a memory buffer, but it can read from or write to a memory location that is outside of the intended boundary of the buffer.