From patchwork Tue Feb 27 20:49:48 2018 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Waiman Long X-Patchwork-Id: 10246037 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork.web.codeaurora.org (Postfix) with ESMTP id 681B3602DC for ; Tue, 27 Feb 2018 20:50:52 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 564E528AD0 for ; Tue, 27 Feb 2018 20:50:52 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 26DF828AF4; Tue, 27 Feb 2018 20:50:52 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.9 required=2.0 tests=BAYES_00,RCVD_IN_DNSWL_HI autolearn=unavailable version=3.3.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id E52D928AB8 for ; Tue, 27 Feb 2018 20:50:30 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751845AbeB0UuD (ORCPT ); Tue, 27 Feb 2018 15:50:03 -0500 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:54326 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751831AbeB0UuB (ORCPT ); Tue, 27 Feb 2018 15:50:01 -0500 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.rdu2.redhat.com [10.11.54.6]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id E8420814DE8B; Tue, 27 Feb 2018 20:50:00 +0000 (UTC) Received: from llong.com (dhcp-17-5.bos.redhat.com [10.18.17.5]) by smtp.corp.redhat.com (Postfix) with ESMTP id B78D22166BC7; Tue, 27 Feb 2018 20:50:00 +0000 (UTC) From: Waiman Long To: "Luis R. Rodriguez" , Kees Cook Cc: linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, Andrew Morton , Al Viro , Waiman Long Subject: [PATCH v2 2/5] sysctl: Add flags to support min/max range clamping Date: Tue, 27 Feb 2018 15:49:48 -0500 Message-Id: <1519764591-27456-3-git-send-email-longman@redhat.com> In-Reply-To: <1519764591-27456-1-git-send-email-longman@redhat.com> References: <1519764591-27456-1-git-send-email-longman@redhat.com> X-Scanned-By: MIMEDefang 2.78 on 10.11.54.6 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.11.55.8]); Tue, 27 Feb 2018 20:50:01 +0000 (UTC) X-Greylist: inspected by milter-greylist-4.5.16 (mx1.redhat.com [10.11.55.8]); Tue, 27 Feb 2018 20:50:01 +0000 (UTC) for IP:'10.11.54.6' DOMAIN:'int-mx06.intmail.prod.int.rdu2.redhat.com' HELO:'smtp.corp.redhat.com' FROM:'longman@redhat.com' RCPT:'' Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP When minimum/maximum values are specified for a sysctl parameter in the ctl_table structure with proc_dointvec_minmax() handler, update to that parameter will fail with error if the given value is outside of the required range. There are use cases where it may be better to clamp the value of the sysctl parameter to the given range without failing the update, especially if the users are not aware of the actual range limits. Reading the value back after the update will now be a good practice to see if the provided value exceeds the range limits. To provide this less restrictive form of range checking, a new flags field is added to the ctl_table structure. The new field is a 16-bit value that just fits into the hole left by the 16-bit umode_t field without increasing the size of the structure. When the CTL_FLAGS_CLAMP_RANGE flag is set in the ctl_table entry, any update from the userspace will be clamped to the given range without error. Signed-off-by: Waiman Long --- include/linux/sysctl.h | 6 ++++++ kernel/sysctl.c | 58 ++++++++++++++++++++++++++++++++++++++++---------- 2 files changed, 53 insertions(+), 11 deletions(-) diff --git a/include/linux/sysctl.h b/include/linux/sysctl.h index b769ecf..eceeaee 100644 --- a/include/linux/sysctl.h +++ b/include/linux/sysctl.h @@ -116,6 +116,7 @@ struct ctl_table void *data; int maxlen; umode_t mode; + uint16_t flags; struct ctl_table *child; /* Deprecated */ proc_handler *proc_handler; /* Callback for text formatting */ struct ctl_table_poll *poll; @@ -123,6 +124,11 @@ struct ctl_table void *extra2; } __randomize_layout; +/* + * ctl_table flags (16 different flags, at most) + */ +#define CTL_FLAGS_CLAMP_RANGE (1 << 0) /* Clamp to min/max range */ + struct ctl_node { struct rb_node node; struct ctl_table_header *header; diff --git a/kernel/sysctl.c b/kernel/sysctl.c index 52b647a..2b2b30c 100644 --- a/kernel/sysctl.c +++ b/kernel/sysctl.c @@ -2505,15 +2505,21 @@ static int proc_dointvec_minmax_sysadmin(struct ctl_table *table, int write, * * The do_proc_dointvec_minmax_conv_param structure provides the * minimum and maximum values for doing range checking for those sysctl - * parameters that use the proc_dointvec_minmax() handler. The error - * code -EINVAL will be returned if the range check fails. + * parameters that use the proc_dointvec_minmax() handler. + * + * The error code -EINVAL will be returned if the range check fails + * and the CTL_FLAGS_CLAMP_RANGE bit is not set in the given flags. + * If that flag is set, the new sysctl value will be clamped to the + * given range without returning any error. * * min: ptr to minimum allowable value * max: ptr to maximum allowable value + * flags: ptr to flags */ struct do_proc_dointvec_minmax_conv_param { int *min; int *max; + uint16_t *flags; }; static int do_proc_dointvec_minmax_conv(bool *negp, unsigned long *lvalp, @@ -2523,9 +2529,21 @@ static int do_proc_dointvec_minmax_conv(bool *negp, unsigned long *lvalp, struct do_proc_dointvec_minmax_conv_param *param = data; if (write) { int val = *negp ? -*lvalp : *lvalp; - if ((param->min && *param->min > val) || - (param->max && *param->max < val)) - return -EINVAL; + bool clamp = param->flags && + (*param->flags & CTL_FLAGS_CLAMP_RANGE); + + if (param->min && *param->min > val) { + if (clamp) + val = *param->min; + else + return -EINVAL; + } + if (param->max && *param->max < val) { + if (clamp) + val = *param->max; + else + return -EINVAL; + } *valp = val; } else { int val = *valp; @@ -2562,6 +2580,7 @@ int proc_dointvec_minmax(struct ctl_table *table, int write, struct do_proc_dointvec_minmax_conv_param param = { .min = (int *) table->extra1, .max = (int *) table->extra2, + .flags = &table->flags, }; return do_proc_dointvec(table, write, buffer, lenp, ppos, do_proc_dointvec_minmax_conv, ¶m); @@ -2572,15 +2591,21 @@ int proc_dointvec_minmax(struct ctl_table *table, int write, * * The do_proc_dointvec_minmax_conv_param structure provides the * minimum and maximum values for doing range checking for those sysctl - * parameters that use the proc_douintvec_minmax() handler. The error - * code -ERANGE will be returned if the range check fails. + * parameters that use the proc_douintvec_minmax() handler. + * + * The error code -ERANGE will be returned if the range check fails + * and the CTL_FLAGS_CLAMP_RANGE bit is not set in the given flags. + * If that flag is set, the new sysctl value will be clamped to the + * given range without returning any error. * * min: ptr to minimum allowable value * max: ptr to maximum allowable value + * flags: ptr to flags */ struct do_proc_douintvec_minmax_conv_param { unsigned int *min; unsigned int *max; + uint16_t *flags; }; static int do_proc_douintvec_minmax_conv(unsigned long *lvalp, @@ -2591,14 +2616,24 @@ static int do_proc_douintvec_minmax_conv(unsigned long *lvalp, if (write) { unsigned int val = *lvalp; + bool clamp = param->flags && + (*param->flags & CTL_FLAGS_CLAMP_RANGE); if (*lvalp > UINT_MAX) return -EINVAL; - if ((param->min && *param->min > val) || - (param->max && *param->max < val)) - return -ERANGE; - + if (param->min && *param->min > val) { + if (clamp) + val = *param->min; + else + return -ERANGE; + } + if (param->max && *param->max < val) { + if (clamp) + val = *param->max; + else + return -ERANGE; + } *valp = val; } else { unsigned int val = *valp; @@ -2633,6 +2668,7 @@ int proc_douintvec_minmax(struct ctl_table *table, int write, struct do_proc_douintvec_minmax_conv_param param = { .min = (unsigned int *) table->extra1, .max = (unsigned int *) table->extra2, + .flags = &table->flags, }; return do_proc_douintvec(table, write, buffer, lenp, ppos, do_proc_douintvec_minmax_conv, ¶m);