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 X-Spam-Level: X-Spam-Status: No, score=-9.1 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,INCLUDES_PATCH,LOTS_OF_MONEY,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_PASS,USER_AGENT_GIT autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 0C6CEC43381 for ; Wed, 27 Mar 2019 18:53:04 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D19E2205C9 for ; Wed, 27 Mar 2019 18:53:03 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1553712783; bh=yChwtWAW1xGyqZqsyQ5Exdv9dH+3dE1pv+0qtoBA+gA=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=W8Ntqnd/0oATwntqcZFVf8XbtGQ5PuIQo2e90bCq3+eSqds7SpqlcNeQTRi2l5GMA gVmdilvSCpqz84JQudLt06XZqpqaxDA1wDOiEf9bUqtnPDzy4z2FuHGfd/Iwe+AFJJ 2XQhe+uVlnhNiPANTPlf2AR54KyA0AS1ujAnGrWI= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2390287AbfC0SR1 (ORCPT ); Wed, 27 Mar 2019 14:17:27 -0400 Received: from mail.kernel.org ([198.145.29.99]:33800 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2390284AbfC0SRZ (ORCPT ); Wed, 27 Mar 2019 14:17:25 -0400 Received: from sasha-vm.mshome.net (c-73-47-72-35.hsd1.nh.comcast.net [73.47.72.35]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 866CA20449; Wed, 27 Mar 2019 18:17:23 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1553710644; bh=yChwtWAW1xGyqZqsyQ5Exdv9dH+3dE1pv+0qtoBA+gA=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=QQiWMfFT32U/nzixAsJNwSbyKTXzME/ocRHlCLIgFApel8zsfwSIHtKItesq6f+FF c5isY6n0mHUf4AkjMp/Zui6D8M1i2JAVn2PGNpIdXOBQb3kLmVlPnCJakqkHV6DVHC Bn5snNKUYSnLst4mP54YzikBu6aW8V4gmYEJZz1E= From: Sasha Levin To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Carlos Maiolino , Jens Axboe , Sasha Levin , linux-fsdevel@vger.kernel.org Subject: [PATCH AUTOSEL 4.14 030/123] fs: fix guard_bio_eod to check for real EOD errors Date: Wed, 27 Mar 2019 14:14:54 -0400 Message-Id: <20190327181628.15899-30-sashal@kernel.org> X-Mailer: git-send-email 2.19.1 In-Reply-To: <20190327181628.15899-1-sashal@kernel.org> References: <20190327181628.15899-1-sashal@kernel.org> MIME-Version: 1.0 X-Patchwork-Hint: Ignore Content-Transfer-Encoding: 8bit Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org From: Carlos Maiolino [ Upstream commit dce30ca9e3b676fb288c33c1f4725a0621361185 ] guard_bio_eod() can truncate a segment in bio to allow it to do IO on odd last sectors of a device. It already checks if the IO starts past EOD, but it does not consider the possibility of an IO request starting within device boundaries can contain more than one segment past EOD. In such cases, truncated_bytes can be bigger than PAGE_SIZE, and will underflow bvec->bv_len. Fix this by checking if truncated_bytes is lower than PAGE_SIZE. This situation has been found on filesystems such as isofs and vfat, which doesn't check the device size before mount, if the device is smaller than the filesystem itself, a readahead on such filesystem, which spans EOD, can trigger this situation, leading a call to zero_user() with a wrong size possibly corrupting memory. I didn't see any crash, or didn't let the system run long enough to check if memory corruption will be hit somewhere, but adding instrumentation to guard_bio_end() to check truncated_bytes size, was enough to see the error. The following script can trigger the error. MNT=/mnt IMG=./DISK.img DEV=/dev/loop0 mkfs.vfat $IMG mount $IMG $MNT cp -R /etc $MNT &> /dev/null umount $MNT losetup -D losetup --find --show --sizelimit 16247280 $IMG mount $DEV $MNT find $MNT -type f -exec cat {} + >/dev/null Kudos to Eric Sandeen for coming up with the reproducer above Reviewed-by: Ming Lei Signed-off-by: Carlos Maiolino Signed-off-by: Jens Axboe Signed-off-by: Sasha Levin --- fs/buffer.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/fs/buffer.c b/fs/buffer.c index 8086cc8ff0bc..bdca7b10e239 100644 --- a/fs/buffer.c +++ b/fs/buffer.c @@ -3084,6 +3084,13 @@ void guard_bio_eod(int op, struct bio *bio) /* Uhhuh. We've got a bio that straddles the device size! */ truncated_bytes = bio->bi_iter.bi_size - (maxsector << 9); + /* + * The bio contains more than one segment which spans EOD, just return + * and let IO layer turn it into an EIO + */ + if (truncated_bytes > bvec->bv_len) + return; + /* Truncate the bio.. */ bio->bi_iter.bi_size -= truncated_bytes; bvec->bv_len -= truncated_bytes; -- 2.19.1