From nobody Wed Sep 3 06:42:33 2025 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id AFD96ECAAA1 for ; Mon, 24 Oct 2022 12:16:47 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233146AbiJXMQq (ORCPT ); Mon, 24 Oct 2022 08:16:46 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:41154 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233383AbiJXMO7 (ORCPT ); Mon, 24 Oct 2022 08:14:59 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 9F4BD7963A; Mon, 24 Oct 2022 04:55:47 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 2F6BA612FE; Mon, 24 Oct 2022 11:55:40 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 45502C433D7; Mon, 24 Oct 2022 11:55:39 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1666612539; bh=AtPuK4+6wjQ0bpEyIlTUi6fm79RRmk4Cm/SAy7YgL4w=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=zKSG+gyFPC1GvqnUUe0SgPNnyrP5UrcMMRF/liRRU1sgP7IzXbUWhx8yZ4D5JASY1 PBuifkj6Og4st26s9lVfJP4AkNA2K9zXH9DS48/BPu4W8/fDhgjW8FppoQchrH6ZXA zGWzLmAk/jv600ClA/IfGzmt8fis2PgzKgFUyMxQ= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Guozihua , Zhongguohua , Al Viro , Theodore Tso , Andrew Lutomirski , "Jason A. Donenfeld" Subject: [PATCH 4.19 026/229] random: restore O_NONBLOCK support Date: Mon, 24 Oct 2022 13:29:05 +0200 Message-Id: <20221024112959.982158381@linuxfoundation.org> X-Mailer: git-send-email 2.38.1 In-Reply-To: <20221024112959.085534368@linuxfoundation.org> References: <20221024112959.085534368@linuxfoundation.org> User-Agent: quilt/0.67 MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" From: Jason A. Donenfeld commit cd4f24ae9404fd31fc461066e57889be3b68641b upstream. Prior to 5.6, when /dev/random was opened with O_NONBLOCK, it would return -EAGAIN if there was no entropy. When the pools were unified in 5.6, this was lost. The post 5.6 behavior of blocking until the pool is initialized, and ignoring O_NONBLOCK in the process, went unnoticed, with no reports about the regression received for two and a half years. However, eventually this indeed did break somebody's userspace. So we restore the old behavior, by returning -EAGAIN if the pool is not initialized. Unlike the old /dev/random, this can only occur during early boot, after which it never blocks again. In order to make this O_NONBLOCK behavior consistent with other expectations, also respect users reading with preadv2(RWF_NOWAIT) and similar. Fixes: 30c08efec888 ("random: make /dev/random be almost like /dev/urandom") Reported-by: Guozihua Reported-by: Zhongguohua Cc: Al Viro Cc: Theodore Ts'o Cc: Andrew Lutomirski Cc: stable@vger.kernel.org Signed-off-by: Jason A. Donenfeld Signed-off-by: Greg Kroah-Hartman --- drivers/char/mem.c | 4 ++-- drivers/char/random.c | 5 +++++ 2 files changed, 7 insertions(+), 2 deletions(-) --- a/drivers/char/mem.c +++ b/drivers/char/mem.c @@ -893,8 +893,8 @@ static const struct memdev { #endif [5] =3D { "zero", 0666, &zero_fops, 0 }, [7] =3D { "full", 0666, &full_fops, 0 }, - [8] =3D { "random", 0666, &random_fops, 0 }, - [9] =3D { "urandom", 0666, &urandom_fops, 0 }, + [8] =3D { "random", 0666, &random_fops, FMODE_NOWAIT }, + [9] =3D { "urandom", 0666, &urandom_fops, FMODE_NOWAIT }, #ifdef CONFIG_PRINTK [11] =3D { "kmsg", 0644, &kmsg_fops, 0 }, #endif --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -1294,6 +1294,11 @@ static ssize_t random_read_iter(struct k { int ret; =20 + if (!crng_ready() && + ((kiocb->ki_flags & IOCB_NOWAIT) || + (kiocb->ki_filp->f_flags & O_NONBLOCK))) + return -EAGAIN; + ret =3D wait_for_random_bytes(); if (ret !=3D 0) return ret;