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=-17.4 required=3.0 tests=DKIMWL_WL_MED,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT, USER_IN_DEF_DKIM_WL 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 1203AC76195 for ; Thu, 18 Jul 2019 19:45:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C6194208C0 for ; Thu, 18 Jul 2019 19:45:52 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="pRCV+LiX" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2404194AbfGRTpv (ORCPT ); Thu, 18 Jul 2019 15:45:51 -0400 Received: from mail-pf1-f201.google.com ([209.85.210.201]:36180 "EHLO mail-pf1-f201.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2404036AbfGRTp1 (ORCPT ); Thu, 18 Jul 2019 15:45:27 -0400 Received: by mail-pf1-f201.google.com with SMTP id e20so17216172pfd.3 for ; Thu, 18 Jul 2019 12:45:26 -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=Qw1hNK3wCX6R4vY8e/8vxPZ6PP8rjnDd+LyVPgBCDkE=; b=pRCV+LiX3uIS6rBZnORlhMPl5flvnryxw9pzdNLnV4RsRiGtXL2vV9B5QRq36fKmZx P+mU/VTMjbfM0ZFiLUdVYr015iychyJ5Mt2SgXuE4WtVg9cLb2kkW+IEdqvZgCHP/HlQ LGFeBS/DvyMIPsFn4NjkYH4bPJlDajjAOtzXkU6uyGcs3wylHTewNonrNZ4fjHlDswgO vHTCu4yzV8YKkmiwXAVvhB+k3ZTVUbbuRpEW3K1V7F8onGzAsUIcrrztKJapBJLGHQLr 0RgVi7zW7oU4uEgd9K9pmjt3pADBRYunWWsKq79demanmkwoOM0CN5YkvoslFXxxdhXh +6sg== 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=Qw1hNK3wCX6R4vY8e/8vxPZ6PP8rjnDd+LyVPgBCDkE=; b=MUhkTG+MquqcGkHKf3/P4KR3mIJBioGh0iM2kuWnj7FqnwrGCwAiV3VhD3Z/TxGG9M ekHcaFr96yUG0ov0zp7HQw887gwXgEOu8I9hJYHD1wHcefN1o6i0+BMRH1si98NvQh5j gIgKpAneJ+5ONNn+DI+UfctdLQ5obh0ljhb5ngVeT7N06AYERNIAGlpwGSmJfgR3SXgz 1/Dmi4Yvxy+XVOQy1tUq4R0GXzxYdl9mVD5FglbuYEyIxOJii8f84YS7HcWyt9EAIxA9 Rp9pRoEikW2iPiGRLpx62HiNCf0gDM3d6BPk8Haga+tUssj8KH1P6ng0DJf7NIHIwhrj TrLA== X-Gm-Message-State: APjAAAUlReBLp7kU5l9Umnh0Ae0zQEh4+EvS7aq7GlXsNtimZO//zsO+ Xn44IfgANt1O66jDfA3128jNMGUBJfyX+rR3NnZGOg== X-Google-Smtp-Source: APXvYqw0b3MspFrMrkYngmKsccdvoswjMjLjdWD+7diBBpS6rTe6CSkRrqT9WJALAnmMCF8TE9+Dud/nR24DK1i9snQlGw== X-Received: by 2002:a65:584f:: with SMTP id s15mr33387767pgr.175.1563479125753; Thu, 18 Jul 2019 12:45:25 -0700 (PDT) Date: Thu, 18 Jul 2019 12:44:12 -0700 In-Reply-To: <20190718194415.108476-1-matthewgarrett@google.com> Message-Id: <20190718194415.108476-27-matthewgarrett@google.com> Mime-Version: 1.0 References: <20190718194415.108476-1-matthewgarrett@google.com> X-Mailer: git-send-email 2.22.0.510.g264f2c817a-goog Subject: [PATCH V36 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 Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 042b688ed124..7b975dbb2bb4 100644 --- a/fs/debugfs/inode.c +++ b/fs/debugfs/inode.c @@ -26,6 +26,7 @@ #include #include #include +#include #include "internal.h" @@ -35,6 +36,32 @@ 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); @@ -369,6 +396,7 @@ 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); @@ -532,7 +560,7 @@ 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) */ @@ -632,7 +660,7 @@ 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", -- 2.22.0.510.g264f2c817a-goog