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=-8.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=ham 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 63937C43331 for ; Tue, 12 Nov 2019 23:22:47 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 37C7F21925 for ; Tue, 12 Nov 2019 23:22:47 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727046AbfKLXWq (ORCPT ); Tue, 12 Nov 2019 18:22:46 -0500 Received: from youngberry.canonical.com ([91.189.89.112]:40934 "EHLO youngberry.canonical.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726932AbfKLXWq (ORCPT ); Tue, 12 Nov 2019 18:22:46 -0500 Received: from [213.220.153.21] (helo=wittgenstein) by youngberry.canonical.com with esmtpsa (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.86_2) (envelope-from ) id 1iUfUe-0005iB-VZ; Tue, 12 Nov 2019 23:22:41 +0000 Date: Wed, 13 Nov 2019 00:22:40 +0100 From: Christian Brauner To: Topi Miettinen Cc: Luis Chamberlain , Kees Cook , Alexey Dobriyan , "linux-kernel@vger.kernel.org" , "open list:FILESYSTEMS (VFS and infrastructure)" , linux-api@vger.kernel.org Subject: Re: [PATCH] Allow restricting permissions in /proc/sys Message-ID: <20191112232239.yevpeemgxz4wy32b@wittgenstein> References: <74a91362-247c-c749-5200-7bdce704ed9e@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <74a91362-247c-c749-5200-7bdce704ed9e@gmail.com> User-Agent: NeoMutt/20180716 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org [Cc+ linux-api@vger.kernel.org] since that's potentially relevant to quite a few people. On Sun, Nov 03, 2019 at 04:55:48PM +0200, Topi Miettinen wrote: > Several items in /proc/sys need not be accessible to unprivileged > tasks. Let the system administrator change the permissions, but only > to more restrictive modes than what the sysctl tables allow. > > Signed-off-by: Topi Miettinen > --- > fs/proc/proc_sysctl.c | 41 +++++++++++++++++++++++++++++++---------- > 1 file changed, 31 insertions(+), 10 deletions(-) > > diff --git a/fs/proc/proc_sysctl.c b/fs/proc/proc_sysctl.c > index d80989b6c344..88c4ca7d2782 100644 > --- a/fs/proc/proc_sysctl.c > +++ b/fs/proc/proc_sysctl.c > @@ -818,6 +818,10 @@ static int proc_sys_permission(struct inode *inode, int > mask) > if ((mask & MAY_EXEC) && S_ISREG(inode->i_mode)) > return -EACCES; > > + error = generic_permission(inode, mask); > + if (error) > + return error; > + > head = grab_header(inode); > if (IS_ERR(head)) > return PTR_ERR(head); > @@ -837,9 +841,35 @@ static int proc_sys_setattr(struct dentry *dentry, > struct iattr *attr) > struct inode *inode = d_inode(dentry); > int error; > > - if (attr->ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID)) > + if (attr->ia_valid & (ATTR_UID | ATTR_GID)) > return -EPERM; > > + if (attr->ia_valid & ATTR_MODE) { > + struct ctl_table_header *head = grab_header(inode); > + struct ctl_table *table = PROC_I(inode)->sysctl_entry; > + umode_t max_mode = 0777; /* Only these bits may change */ > + > + if (IS_ERR(head)) > + return PTR_ERR(head); > + > + if (!table) /* global root - r-xr-xr-x */ > + max_mode &= ~0222; > + else /* > + * Don't allow permissions to become less > + * restrictive than the sysctl table entry > + */ > + max_mode &= table->mode; > + > + sysctl_head_finish(head); > + > + /* Execute bits only allowed for directories */ > + if (!S_ISDIR(inode->i_mode)) > + max_mode &= ~0111; > + > + if (attr->ia_mode & ~S_IFMT & ~max_mode) > + return -EPERM; > + } > + > error = setattr_prepare(dentry, attr); > if (error) > return error; > @@ -853,17 +883,8 @@ static int proc_sys_getattr(const struct path *path, > struct kstat *stat, > u32 request_mask, unsigned int query_flags) > { > struct inode *inode = d_inode(path->dentry); > - struct ctl_table_header *head = grab_header(inode); > - struct ctl_table *table = PROC_I(inode)->sysctl_entry; > - > - if (IS_ERR(head)) > - return PTR_ERR(head); > > generic_fillattr(inode, stat); > - if (table) > - stat->mode = (stat->mode & S_IFMT) | table->mode; > - > - sysctl_head_finish(head); > return 0; > } > > -- > 2.24.0.rc1 >