Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933508AbeALAzr (ORCPT + 1 other); Thu, 11 Jan 2018 19:55:47 -0500 Received: from mga04.intel.com ([192.55.52.120]:8576 "EHLO mga04.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933411AbeALAzp (ORCPT ); Thu, 11 Jan 2018 19:55:45 -0500 X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.46,346,1511856000"; d="scan'208";a="9761357" Subject: [PATCH v2 12/19] userns: prevent bounds-check bypass via speculative execution From: Dan Williams To: linux-kernel@vger.kernel.org Cc: linux-arch@vger.kernel.org, kernel-hardening@lists.openwall.com, "Eric W. Biederman" , akpm@linux-foundation.org, torvalds@linux-foundation.org, tglx@linutronix.de, Elena Reshetova , alan@linux.intel.com Date: Thu, 11 Jan 2018 16:47:29 -0800 Message-ID: <151571804955.27429.6378685761369089453.stgit@dwillia2-desk3.amr.corp.intel.com> In-Reply-To: <151571798296.27429.7166552848688034184.stgit@dwillia2-desk3.amr.corp.intel.com> References: <151571798296.27429.7166552848688034184.stgit@dwillia2-desk3.amr.corp.intel.com> User-Agent: StGit/0.17.1-9-g687f MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Return-Path: Static analysis reports that 'pos' may be a user controlled value that is used as a data dependency determining which extent to return out of 'map'. In order to avoid potential leaks of kernel memory values, block speculative execution of the instruction stream that could issue further reads based on an invalid speculative result from 'm_start()'. Based on an original patch by Elena Reshetova. Cc: "Eric W. Biederman" Signed-off-by: Elena Reshetova Signed-off-by: Dan Williams --- kernel/user_namespace.c | 11 +++++------ 1 file changed, 5 insertions(+), 6 deletions(-) diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c index 246d4d4ce5c7..8c803eae186f 100644 --- a/kernel/user_namespace.c +++ b/kernel/user_namespace.c @@ -20,6 +20,7 @@ #include #include #include +#include #include #include #include @@ -648,15 +649,13 @@ static void *m_start(struct seq_file *seq, loff_t *ppos, { loff_t pos = *ppos; unsigned extents = map->nr_extents; - smp_rmb(); - if (pos >= extents) - return NULL; + /* paired with smp_wmb in map_write */ + smp_rmb(); if (extents <= UID_GID_MAP_MAX_BASE_EXTENTS) - return &map->extent[pos]; - - return &map->forward[pos]; + return array_ptr(map->extent, pos, extents); + return array_ptr(map->forward, pos, extents); } static void *uid_m_start(struct seq_file *seq, loff_t *ppos)