From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757040AbbLBUxW (ORCPT ); Wed, 2 Dec 2015 15:53:22 -0500 Received: from smtp.outflux.net ([198.145.64.163]:36363 "EHLO smtp.outflux.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757008AbbLBUxT (ORCPT ); Wed, 2 Dec 2015 15:53:19 -0500 Date: Wed, 2 Dec 2015 12:53:16 -0800 From: Kees Cook To: Andrew Morton Cc: linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH] sysctl: enable strict writes Message-ID: <20151202205316.GA1331@www.outflux.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline X-HELO: www.outflux.net Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org SYSCTL_WRITES_WARN was added in f4aacea2f5d1a ("sysctl: allow for strict write position handling"), and released in v3.16 in August of 2014. Since then I can find only 1 instance of non-zero offset writing[1], and it was fixed immediately in CRIU[2]. As such, it appears safe to flip this to the strict state now. [1] https://www.google.com/search?q="when%20file%20position%20was%20not%200" [2] http://lists.openvz.org/pipermail/criu/2015-April/019819.html Signed-off-by: Kees Cook --- Documentation/sysctl/kernel.txt | 15 +++++++-------- kernel/sysctl.c | 2 +- 2 files changed, 8 insertions(+), 9 deletions(-) diff --git a/Documentation/sysctl/kernel.txt b/Documentation/sysctl/kernel.txt index af70d1541d3a..be61d53e997f 100644 --- a/Documentation/sysctl/kernel.txt +++ b/Documentation/sysctl/kernel.txt @@ -810,14 +810,13 @@ via the /proc/sys interface: Each write syscall must fully contain the sysctl value to be written, and multiple writes on the same sysctl file descriptor will rewrite the sysctl value, regardless of file position. - 0 - (default) Same behavior as above, but warn about processes that - perform writes to a sysctl file descriptor when the file position - is not 0. - 1 - Respect file position when writing sysctl strings. Multiple writes - will append to the sysctl value buffer. Anything past the max length - of the sysctl value buffer will be ignored. Writes to numeric sysctl - entries must always be at file position 0 and the value must be - fully contained in the buffer sent in the write syscall. + 0 - Same behavior as above, but warn about processes that perform writes + to a sysctl file descriptor when the file position is not 0. + 1 - (default) Respect file position when writing sysctl strings. Multiple + writes will append to the sysctl value buffer. Anything past the max + length of the sysctl value buffer will be ignored. Writes to numeric + sysctl entries must always be at file position 0 and the value must + be fully contained in the buffer sent in the write syscall. ============================================================== diff --git a/kernel/sysctl.c b/kernel/sysctl.c index dc6858d6639e..081873afba6b 100644 --- a/kernel/sysctl.c +++ b/kernel/sysctl.c @@ -173,7 +173,7 @@ extern int no_unaligned_warning; #define SYSCTL_WRITES_WARN 0 #define SYSCTL_WRITES_STRICT 1 -static int sysctl_writes_strict = SYSCTL_WRITES_WARN; +static int sysctl_writes_strict = SYSCTL_WRITES_STRICT; static int proc_do_cad_pid(struct ctl_table *table, int write, void __user *buffer, size_t *lenp, loff_t *ppos); -- 1.9.1 -- Kees Cook Chrome OS & Brillo Security