static int md4_update(struct shash_desc *desc, const u8 *data, unsigned int len)
{
	struct md4_ctx *mctx = shash_desc_ctx(desc);
	const u32 avail = sizeof(mctx->block) - (mctx->byte_count & 0x3f);

	mctx->byte_count += len;

	if (avail > len) {
		memcpy((char *)mctx->block + (sizeof(mctx->block) - avail),
		       data, len);
		return 0;
	}

	memcpy((char *)mctx->block + (sizeof(mctx->block) - avail),
	       data, avail);

	md4_transform_helper(mctx);
	data += avail;
	len -= avail;

	while (len >= sizeof(mctx->block)) {
		memcpy(mctx->block, data, sizeof(mctx->block));
		md4_transform_helper(mctx);
		data += sizeof(mctx->block);
		len -= sizeof(mctx->block);
	}

	memcpy(mctx->block, data, len);

	return 0;
}

This category addresses vulnerabilities caused by flawed access control mechanisms, where incorrect permission settings allow unauthorized users to access restricted resources.