From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755928AbcBWVzl (ORCPT ); Tue, 23 Feb 2016 16:55:41 -0500 Received: from shadbolt.e.decadent.org.uk ([88.96.1.126]:41685 "EHLO shadbolt.e.decadent.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755590AbcBWVo4 (ORCPT ); Tue, 23 Feb 2016 16:44:56 -0500 Content-Type: text/plain; charset="UTF-8" Content-Disposition: inline Content-Transfer-Encoding: 8bit MIME-Version: 1.0 From: Ben Hutchings To: linux-kernel@vger.kernel.org, stable@vger.kernel.org CC: akpm@linux-foundation.org Date: Tue, 23 Feb 2016 21:42:03 +0000 Message-ID: X-Mailer: LinuxStableQueue (scripts by bwh) Subject: [PATCH 3.2 66/67] pipe: Fix buffer offset after partially failed read In-Reply-To: X-SA-Exim-Connect-IP: 92.40.248.141 X-SA-Exim-Mail-From: ben@decadent.org.uk X-SA-Exim-Scanned: No (on shadbolt.decadent.org.uk); SAEximRunCond expanded to false Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 3.2.78-rc1 review patch. If anyone has any objections, please let me know. ------------------ From: Ben Hutchings Quoting the RHEL advisory: > It was found that the fix for CVE-2015-1805 incorrectly kept buffer > offset and buffer length in sync on a failed atomic read, potentially > resulting in a pipe buffer state corruption. A local, unprivileged user > could use this flaw to crash the system or leak kernel memory to user > space. (CVE-2016-0774, Moderate) The same flawed fix was applied to stable branches from 2.6.32.y to 3.14.y inclusive, and I was able to reproduce the issue on 3.2.y. We need to give pipe_iov_copy_to_user() a separate offset variable and only update the buffer offset if it succeeds. References: https://rhn.redhat.com/errata/RHSA-2016-0103.html Signed-off-by: Ben Hutchings --- --- a/fs/pipe.c +++ b/fs/pipe.c @@ -395,6 +395,7 @@ pipe_read(struct kiocb *iocb, const stru void *addr; size_t chars = buf->len, remaining; int error, atomic; + int offset; if (chars > total_len) chars = total_len; @@ -408,9 +409,10 @@ pipe_read(struct kiocb *iocb, const stru atomic = !iov_fault_in_pages_write(iov, chars); remaining = chars; + offset = buf->offset; redo: addr = ops->map(pipe, buf, atomic); - error = pipe_iov_copy_to_user(iov, addr, &buf->offset, + error = pipe_iov_copy_to_user(iov, addr, &offset, &remaining, atomic); ops->unmap(pipe, buf, addr); if (unlikely(error)) { @@ -426,6 +428,7 @@ redo: break; } ret += chars; + buf->offset += chars; buf->len -= chars; /* Was it a packet buffer? Clean up and exit */