From patchwork Thu Aug 8 00:07:18 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Matthew Garrett X-Patchwork-Id: 11082943 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id A199913B1 for ; Thu, 8 Aug 2019 00:08:53 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 9184F28AB7 for ; Thu, 8 Aug 2019 00:08:53 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 82D9328ACB; Thu, 8 Aug 2019 00:08:53 +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=-14.5 required=2.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,RCVD_IN_DNSWL_HI,USER_IN_DEF_DKIM_WL autolearn=ham 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 CF28F28AB7 for ; Thu, 8 Aug 2019 00:08:52 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2389767AbfHHAIe (ORCPT ); Wed, 7 Aug 2019 20:08:34 -0400 Received: from mail-pf1-f201.google.com ([209.85.210.201]:36984 "EHLO mail-pf1-f201.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2389765AbfHHAIc (ORCPT ); Wed, 7 Aug 2019 20:08:32 -0400 Received: by mail-pf1-f201.google.com with SMTP id x18so57784557pfj.4 for ; Wed, 07 Aug 2019 17:08:32 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=date:in-reply-to:message-id:mime-version:references:subject:from:to :cc; bh=ntXMs3tuU1WJWAT2FcG/TTitDVr73WJt0FGo+YbSY68=; b=CFneMqNiJ9OrjNIQ8spvu4sz6eGRJcgaKvwI1rPo4D9clDhadqGsOSqFRFwjWgirY7 bOq4XK/V0/rZ2T5ARuyQfGXsAW7vFCWdDMAQpZjuAUE5AuZlWTYAV3yl+S0O0LXOS+6X XT41HBcc6UGpNY0tgjZpiQ4V/UDTdkpzSdCxdqB932dUSJFofoHGCBvHMJd8Hyrg6gE/ uufPpvlKKzakljmTKGGS8+3/MjChfN7uSFDLO7oJD2bSwY+m5d9lQtFGu4xkeOyGg17+ RFgJwygZi6doYOuOdaYSmQcNq0PeNPM1xYgBouBoEPk6Vw3JA3HzON9cVr8HIX1Hdfpv 9mBg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:in-reply-to:message-id:mime-version :references:subject:from:to:cc; bh=ntXMs3tuU1WJWAT2FcG/TTitDVr73WJt0FGo+YbSY68=; b=K9arhCZZlGh3OS228JU31VtKJimK9aSyoS/NOnsCEDRzA2wzzeMa+/rbt82mQhC6Y1 6kpbgWYs2o+IJ8vYzVMIXY+Qk0/Zztlya//QIdh1eP9qs49gsrQyhD/DTcZY4HDx7dfh bM+8bmuDh3AhdFoh9+VGST/kofcpyoWTAq7nIxNOq4Kw19MspmoFy8Qj9V8Nfy/1gVA5 FearmiuPWkdFI4MXIJW5WKWLCctC+X/gXp91rvz11KZmJuemikNHBoDAM/R1e+7AsVcz 04tV9d7+ym23rJWeLdBcLbfHsT5iqVGkgd9VEdOK/zMyGx+2/UMHLzgBAoSrVydsNb3U qYMg== X-Gm-Message-State: APjAAAWFyA49KzooHtTT3u6trccpFIjCLPJAEqe0v4pEU7QIStjDuiiO 0Fs2LB8m3EkfS2udbP3jJkOzRIQk2fKWpQV75g2nMQ== X-Google-Smtp-Source: APXvYqxhTw0/9vwmNZBBg2HFtn2EcQgfcCUjP+04jbBIv7nnQKYPA/Dz0cf3aORrMACkdJVlfwK4BWSkChYLpoDxae1bzQ== X-Received: by 2002:a63:7a06:: with SMTP id v6mr10178668pgc.115.1565222911762; Wed, 07 Aug 2019 17:08:31 -0700 (PDT) Date: Wed, 7 Aug 2019 17:07:18 -0700 In-Reply-To: <20190808000721.124691-1-matthewgarrett@google.com> Message-Id: <20190808000721.124691-27-matthewgarrett@google.com> Mime-Version: 1.0 References: <20190808000721.124691-1-matthewgarrett@google.com> X-Mailer: git-send-email 2.22.0.770.g0f2c4a37fd-goog Subject: [PATCH V38 26/29] debugfs: Restrict debugfs when the kernel is locked down From: Matthew Garrett To: jmorris@namei.org Cc: linux-security-module@vger.kernel.org, linux-kernel@vger.kernel.org, linux-api@vger.kernel.org, David Howells , Andy Shevchenko , acpi4asus-user@lists.sourceforge.net, platform-driver-x86@vger.kernel.org, Matthew Garrett , Thomas Gleixner , Greg KH , "Rafael J . Wysocki" , Matthew Garrett Sender: owner-linux-security-module@vger.kernel.org Precedence: bulk List-ID: X-Virus-Scanned: ClamAV using ClamSMTP From: David Howells Disallow opening of debugfs files that might be used to muck around when the kernel is locked down as various drivers give raw access to hardware through debugfs. Given the effort of auditing all 2000 or so files and manually fixing each one as necessary, I've chosen to apply a heuristic instead. The following changes are made: (1) chmod and chown are disallowed on debugfs objects (though the root dir can be modified by mount and remount, but I'm not worried about that). (2) When the kernel is locked down, only files with the following criteria are permitted to be opened: - The file must have mode 00444 - The file must not have ioctl methods - The file must not have mmap (3) When the kernel is locked down, files may only be opened for reading. Normal device interaction should be done through configfs, sysfs or a miscdev, not debugfs. Note that this makes it unnecessary to specifically lock down show_dsts(), show_devs() and show_call() in the asus-wmi driver. I would actually prefer to lock down all files by default and have the the files unlocked by the creator. This is tricky to manage correctly, though, as there are 19 creation functions and ~1600 call sites (some of them in loops scanning tables). Signed-off-by: David Howells cc: Andy Shevchenko cc: acpi4asus-user@lists.sourceforge.net cc: platform-driver-x86@vger.kernel.org cc: Matthew Garrett cc: Thomas Gleixner Cc: Greg KH Cc: Rafael J. Wysocki Signed-off-by: Matthew Garrett --- fs/debugfs/file.c | 30 ++++++++++++++++++++++++++++++ fs/debugfs/inode.c | 32 ++++++++++++++++++++++++++++++-- include/linux/security.h | 1 + security/lockdown/lockdown.c | 1 + 4 files changed, 62 insertions(+), 2 deletions(-) diff --git a/fs/debugfs/file.c b/fs/debugfs/file.c index 93e4ca6b2ad7..87846aad594b 100644 --- a/fs/debugfs/file.c +++ b/fs/debugfs/file.c @@ -19,6 +19,7 @@ #include #include #include +#include #include "internal.h" @@ -136,6 +137,25 @@ void debugfs_file_put(struct dentry *dentry) } EXPORT_SYMBOL_GPL(debugfs_file_put); +/* + * Only permit access to world-readable files when the kernel is locked down. + * We also need to exclude any file that has ways to write or alter it as root + * can bypass the permissions check. + */ +static bool debugfs_is_locked_down(struct inode *inode, + struct file *filp, + const struct file_operations *real_fops) +{ + if ((inode->i_mode & 07777) == 0444 && + !(filp->f_mode & FMODE_WRITE) && + !real_fops->unlocked_ioctl && + !real_fops->compat_ioctl && + !real_fops->mmap) + return false; + + return security_locked_down(LOCKDOWN_DEBUGFS); +} + static int open_proxy_open(struct inode *inode, struct file *filp) { struct dentry *dentry = F_DENTRY(filp); @@ -147,6 +167,11 @@ static int open_proxy_open(struct inode *inode, struct file *filp) return r == -EIO ? -ENOENT : r; real_fops = debugfs_real_fops(filp); + + r = debugfs_is_locked_down(inode, filp, real_fops); + if (r) + goto out; + real_fops = fops_get(real_fops); if (!real_fops) { /* Huh? Module did not clean up after itself at exit? */ @@ -272,6 +297,11 @@ static int full_proxy_open(struct inode *inode, struct file *filp) return r == -EIO ? -ENOENT : r; real_fops = debugfs_real_fops(filp); + + r = debugfs_is_locked_down(inode, filp, real_fops); + if (r) + goto out; + real_fops = fops_get(real_fops); if (!real_fops) { /* Huh? Module did not cleanup after itself at exit? */ diff --git a/fs/debugfs/inode.c b/fs/debugfs/inode.c index ec5c197985ec..51ced4ae9280 100644 --- a/fs/debugfs/inode.c +++ b/fs/debugfs/inode.c @@ -27,6 +27,7 @@ #include #include #include +#include #include "internal.h" @@ -36,6 +37,32 @@ static struct vfsmount *debugfs_mount; static int debugfs_mount_count; static bool debugfs_registered; +/* + * Don't allow access attributes to be changed whilst the kernel is locked down + * so that we can use the file mode as part of a heuristic to determine whether + * to lock down individual files. + */ +static int debugfs_setattr(struct dentry *dentry, struct iattr *ia) +{ + int ret = security_locked_down(LOCKDOWN_DEBUGFS); + + if (ret && (ia->ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID))) + return ret; + return simple_setattr(dentry, ia); +} + +static const struct inode_operations debugfs_file_inode_operations = { + .setattr = debugfs_setattr, +}; +static const struct inode_operations debugfs_dir_inode_operations = { + .lookup = simple_lookup, + .setattr = debugfs_setattr, +}; +static const struct inode_operations debugfs_symlink_inode_operations = { + .get_link = simple_get_link, + .setattr = debugfs_setattr, +}; + static struct inode *debugfs_get_inode(struct super_block *sb) { struct inode *inode = new_inode(sb); @@ -353,6 +380,7 @@ static struct dentry *__debugfs_create_file(const char *name, umode_t mode, inode->i_mode = mode; inode->i_private = data; + inode->i_op = &debugfs_file_inode_operations; inode->i_fop = proxy_fops; dentry->d_fsdata = (void *)((unsigned long)real_fops | DEBUGFS_FSDATA_IS_REAL_FOPS_BIT); @@ -516,7 +544,7 @@ struct dentry *debugfs_create_dir(const char *name, struct dentry *parent) } inode->i_mode = S_IFDIR | S_IRWXU | S_IRUGO | S_IXUGO; - inode->i_op = &simple_dir_inode_operations; + inode->i_op = &debugfs_dir_inode_operations; inode->i_fop = &simple_dir_operations; /* directory inodes start off with i_nlink == 2 (for "." entry) */ @@ -616,7 +644,7 @@ struct dentry *debugfs_create_symlink(const char *name, struct dentry *parent, return failed_creating(dentry); } inode->i_mode = S_IFLNK | S_IRWXUGO; - inode->i_op = &simple_symlink_inode_operations; + inode->i_op = &debugfs_symlink_inode_operations; inode->i_link = link; d_instantiate(dentry, inode); return end_creating(dentry); diff --git a/include/linux/security.h b/include/linux/security.h index 8ef366de70b0..d92323b44a3f 100644 --- a/include/linux/security.h +++ b/include/linux/security.h @@ -115,6 +115,7 @@ enum lockdown_reason { LOCKDOWN_TIOCSSERIAL, LOCKDOWN_MODULE_PARAMETERS, LOCKDOWN_MMIOTRACE, + LOCKDOWN_DEBUGFS, LOCKDOWN_INTEGRITY_MAX, LOCKDOWN_KCORE, LOCKDOWN_KPROBES, diff --git a/security/lockdown/lockdown.c b/security/lockdown/lockdown.c index fb437a7ef5f2..88064ce1c844 100644 --- a/security/lockdown/lockdown.c +++ b/security/lockdown/lockdown.c @@ -30,6 +30,7 @@ static char *lockdown_reasons[LOCKDOWN_CONFIDENTIALITY_MAX+1] = { [LOCKDOWN_TIOCSSERIAL] = "reconfiguration of serial port IO", [LOCKDOWN_MODULE_PARAMETERS] = "unsafe module parameters", [LOCKDOWN_MMIOTRACE] = "unsafe mmio", + [LOCKDOWN_DEBUGFS] = "debugfs access", [LOCKDOWN_INTEGRITY_MAX] = "integrity", [LOCKDOWN_KCORE] = "/proc/kcore access", [LOCKDOWN_KPROBES] = "use of kprobes",