From mboxrd@z Thu Jan 1 00:00:00 1970 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 9A1FCCCA489 for ; Mon, 20 Jun 2022 14:01:29 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1350076AbiFTOBH (ORCPT ); Mon, 20 Jun 2022 10:01:07 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44198 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1350741AbiFTNxt (ORCPT ); Mon, 20 Jun 2022 09:53:49 -0400 Received: from ams.source.kernel.org (ams.source.kernel.org [145.40.68.75]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 56B6B1AF37; Mon, 20 Jun 2022 06:20:16 -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 ams.source.kernel.org (Postfix) with ESMTPS id 9D176B811C2; Mon, 20 Jun 2022 13:19:11 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 10405C3411B; Mon, 20 Jun 2022 13:19:09 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1655731150; bh=OxBmzqVqX1mREF4WkljC/7yQplxzyWhFgFPRZ33k3wY=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=mnqh5EN3Nb7PqS4qvqDmasDmSr8UA8K3hBq5WSTxs5dL5M5FSv32ajf1RC2HOZtN7 gHI5JsE1N5A7NUrt0CmAM/6W1gjU9Rr3UuM4BQSZEaHzvmvgLsA5OkW4Ye6leocmKi WXubHdLR9B/p33c0/ukvDmHWY+uKls1+CIKeIA5E= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Dominik Brodowski , "Jason A. Donenfeld" Subject: [PATCH 5.4 170/240] random: check for signals after page of pool writes Date: Mon, 20 Jun 2022 14:51:11 +0200 Message-Id: <20220620124743.925904797@linuxfoundation.org> X-Mailer: git-send-email 2.36.1 In-Reply-To: <20220620124737.799371052@linuxfoundation.org> References: <20220620124737.799371052@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: "Jason A. Donenfeld" commit 1ce6c8d68f8ac587f54d0a271ac594d3d51f3efb upstream. get_random_bytes_user() checks for signals after producing a PAGE_SIZE worth of output, just like /dev/zero does. write_pool() is doing basically the same work (actually, slightly more expensive), and so should stop to check for signals in the same way. Let's also name it write_pool_user() to match get_random_bytes_user(), so this won't be misused in the future. Before this patch, massive writes to /dev/urandom would tie up the process for an extremely long time and make it unterminatable. After, it can be successfully interrupted. The following test program can be used to see this works as intended: #include #include #include #include static unsigned char x[~0U]; static void handle(int) { } int main(int argc, char *argv[]) { pid_t pid = getpid(), child; int fd; signal(SIGUSR1, handle); if (!(child = fork())) { for (;;) kill(pid, SIGUSR1); } fd = open("/dev/urandom", O_WRONLY); pause(); printf("interrupted after writing %zd bytes\n", write(fd, x, sizeof(x))); close(fd); kill(child, SIGTERM); return 0; } Result before: "interrupted after writing 2147479552 bytes" Result after: "interrupted after writing 4096 bytes" Cc: Dominik Brodowski Signed-off-by: Jason A. Donenfeld Signed-off-by: Greg Kroah-Hartman --- drivers/char/random.c | 14 ++++++++++---- 1 file changed, 10 insertions(+), 4 deletions(-) --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -1251,7 +1251,7 @@ static __poll_t random_poll(struct file return crng_ready() ? EPOLLIN | EPOLLRDNORM : EPOLLOUT | EPOLLWRNORM; } -static ssize_t write_pool(struct iov_iter *iter) +static ssize_t write_pool_user(struct iov_iter *iter) { u8 block[BLAKE2S_BLOCK_SIZE]; ssize_t ret = 0; @@ -1266,7 +1266,13 @@ static ssize_t write_pool(struct iov_ite mix_pool_bytes(block, copied); if (!iov_iter_count(iter) || copied != sizeof(block)) break; - cond_resched(); + + BUILD_BUG_ON(PAGE_SIZE % sizeof(block) != 0); + if (ret % PAGE_SIZE == 0) { + if (signal_pending(current)) + break; + cond_resched(); + } } memzero_explicit(block, sizeof(block)); @@ -1275,7 +1281,7 @@ static ssize_t write_pool(struct iov_ite static ssize_t random_write_iter(struct kiocb *kiocb, struct iov_iter *iter) { - return write_pool(iter); + return write_pool_user(iter); } static ssize_t urandom_read_iter(struct kiocb *kiocb, struct iov_iter *iter) @@ -1342,7 +1348,7 @@ static long random_ioctl(struct file *f, ret = import_single_range(WRITE, p, len, &iov, &iter); if (unlikely(ret)) return ret; - ret = write_pool(&iter); + ret = write_pool_user(&iter); if (unlikely(ret < 0)) return ret; /* Since we're crediting, enforce that it was all written into the pool. */