From patchwork Wed Aug 19 16:43:16 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Ross Zwisler X-Patchwork-Id: 255274 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=-17.9 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH, MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING, SIGNED_OFF_BY, SPF_HELO_NONE, SPF_PASS, URIBL_BLOCKED, USER_AGENT_GIT autolearn=unavailable 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 98AF4C433E1 for ; Wed, 19 Aug 2020 16:43:42 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 72B4A208A9 for ; Wed, 19 Aug 2020 16:43:42 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=chromium.org header.i=@chromium.org header.b="oQrKEZqO" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726731AbgHSQnb (ORCPT ); Wed, 19 Aug 2020 12:43:31 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:42944 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726461AbgHSQn0 (ORCPT ); Wed, 19 Aug 2020 12:43:26 -0400 Received: from mail-oo1-xc42.google.com (mail-oo1-xc42.google.com [IPv6:2607:f8b0:4864:20::c42]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 3AFE6C061383 for ; Wed, 19 Aug 2020 09:43:26 -0700 (PDT) Received: by mail-oo1-xc42.google.com with SMTP id j19so5018860oor.2 for ; Wed, 19 Aug 2020 09:43:26 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=chromium.org; s=google; h=from:to:cc:subject:date:message-id:mime-version :content-transfer-encoding; bh=fHtiyHduMLuRLeSYVULskmD3eviA1+GnUpgLjTZc2NY=; b=oQrKEZqORIk9R0UwmTBg5mgKl6sr3zgh18kc6CBOZ1pad8zDks+B4cNffrlmcb4ntD 4Le1Dcva8QTtqOlngwBSywEDFptBbab+gVR/fVdpsU9vpZkhSezMXEGuFNByLWUlgVQn 0ZpYuWEXo//S4rRHtIk3YK4d9iIPtOi9wBj0w= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:date:message-id:mime-version :content-transfer-encoding; bh=fHtiyHduMLuRLeSYVULskmD3eviA1+GnUpgLjTZc2NY=; b=pw1ydI4/V4Pl8NSNGN1vInOZ10EJh1CyF2R2gsqfbMzP8Y+Z85anutlWwCabySxbUy Jdue/eihqUFp88EwPX9q6W58Suq3v8nZs4cgwERpCH1nwebGhy9Uyhked+io/YphFFUw 7UfRKh22yk/VK3XPmeqUhuVkijN2tb0f4JkYERGEqatoH6MNEUIpMCxlwIr+wiYh3R0A A1tKqCZBtXp93GBd1h/atBvfVBHwKXSx2ol1LPHodDCfz70BU5Nifmp6THoQPBUZyEDG s6qHnWHSILppkPhYOkPIYhRB6P4z3rczm9RPfaY8TKLqyg8qqlEwI7kdt+8/sjdNl/j+ dbwA== X-Gm-Message-State: AOAM533twU8Mwv0wkG+jKHFdyR9KwI5X/sSmH+n4XgYkc6/7hVwQnK0Z ZqRm9t3As8MNTbloYxd154bvyQ== X-Google-Smtp-Source: ABdhPJz8CYYAnJTKUGBNqv3snd38wIzCI9/fcynxM2uB7imMbOtN1VEPxzxY5VjIfcsHyE+mD/1Wbg== X-Received: by 2002:a4a:de11:: with SMTP id y17mr18767887oot.29.1597855405443; Wed, 19 Aug 2020 09:43:25 -0700 (PDT) Received: from ravnica.hsd1.co.comcast.net ([2601:285:8380:9270::f2a2]) by smtp.gmail.com with ESMTPSA id z72sm4520036ooa.42.2020.08.19.09.43.23 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 19 Aug 2020 09:43:24 -0700 (PDT) From: Ross Zwisler X-Google-Original-From: Ross Zwisler To: Alexander Viro , linux-kernel@vger.kernel.org Cc: Mattias Nissler , Aleksa Sarai , Andrew Morton , Benjamin Gordon , David Howells , Dmitry Torokhov , Jesse Barnes , linux-fsdevel@vger.kernel.org, linux-kselftest@vger.kernel.org, Matthew Wilcox , Micah Morton , Raul Rangel , Shuah Khan , Ross Zwisler Subject: [PATCH v8 1/2] Add a "nosymfollow" mount option. Date: Wed, 19 Aug 2020 10:43:16 -0600 Message-Id: <20200819164317.637421-1-zwisler@google.com> X-Mailer: git-send-email 2.28.0.220.ged08abb693-goog MIME-Version: 1.0 Sender: linux-kselftest-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kselftest@vger.kernel.org From: Mattias Nissler For mounts that have the new "nosymfollow" option, don't follow symlinks when resolving paths. The new option is similar in spirit to the existing "nodev", "noexec", and "nosuid" options, as well as to the LOOKUP_NO_SYMLINKS resolve flag in the openat2(2) syscall. Various BSD variants have been supporting the "nosymfollow" mount option for a long time with equivalent implementations. Note that symlinks may still be created on file systems mounted with the "nosymfollow" option present. readlink() remains functional, so user space code that is aware of symlinks can still choose to follow them explicitly. Setting the "nosymfollow" mount option helps prevent privileged writers from modifying files unintentionally in case there is an unexpected link along the accessed path. The "nosymfollow" option is thus useful as a defensive measure for systems that need to deal with untrusted file systems in privileged contexts. More information on the history and motivation for this patch can be found here: https://sites.google.com/a/chromium.org/dev/chromium-os/chromiumos-design-docs/hardening-against-malicious-stateful-data#TOC-Restricting-symlink-traversal Signed-off-by: Mattias Nissler Signed-off-by: Ross Zwisler Reviewed-by: Aleksa Sarai --- Changes since v7 [1]: * Rebased onto v5.9-rc1. * Added selftest in second patch. * Added Aleska's Reviewed-By tag. Thank you for the review! After this lands I will upstream changes to util-linux[2] and man-pages [3]. [1]: https://lkml.org/lkml/2020/8/11/896 [2]: https://github.com/rzwisler/util-linux/commit/7f8771acd85edb70d97921c026c55e1e724d4e15 [3]: https://github.com/rzwisler/man-pages/commit/b8fe8079f64b5068940c0144586e580399a71668 --- fs/namei.c | 3 ++- fs/namespace.c | 2 ++ fs/proc_namespace.c | 1 + fs/statfs.c | 2 ++ include/linux/mount.h | 3 ++- include/linux/statfs.h | 1 + include/uapi/linux/mount.h | 1 + 7 files changed, 11 insertions(+), 2 deletions(-) diff --git a/fs/namei.c b/fs/namei.c index e99e2a9da0f7d..12d92af2e2ca7 100644 --- a/fs/namei.c +++ b/fs/namei.c @@ -1626,7 +1626,8 @@ static const char *pick_link(struct nameidata *nd, struct path *link, return ERR_PTR(error); } - if (unlikely(nd->flags & LOOKUP_NO_SYMLINKS)) + if (unlikely(nd->flags & LOOKUP_NO_SYMLINKS) || + unlikely(nd->path.mnt->mnt_flags & MNT_NOSYMFOLLOW)) return ERR_PTR(-ELOOP); if (!(nd->flags & LOOKUP_RCU)) { diff --git a/fs/namespace.c b/fs/namespace.c index bae0e95b3713a..6408788a649e1 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -3160,6 +3160,8 @@ int path_mount(const char *dev_name, struct path *path, mnt_flags &= ~(MNT_RELATIME | MNT_NOATIME); if (flags & MS_RDONLY) mnt_flags |= MNT_READONLY; + if (flags & MS_NOSYMFOLLOW) + mnt_flags |= MNT_NOSYMFOLLOW; /* The default atime for remount is preservation */ if ((flags & MS_REMOUNT) && diff --git a/fs/proc_namespace.c b/fs/proc_namespace.c index 3059a9394c2d6..e59d4bb3a89e4 100644 --- a/fs/proc_namespace.c +++ b/fs/proc_namespace.c @@ -70,6 +70,7 @@ static void show_mnt_opts(struct seq_file *m, struct vfsmount *mnt) { MNT_NOATIME, ",noatime" }, { MNT_NODIRATIME, ",nodiratime" }, { MNT_RELATIME, ",relatime" }, + { MNT_NOSYMFOLLOW, ",nosymfollow" }, { 0, NULL } }; const struct proc_fs_opts *fs_infop; diff --git a/fs/statfs.c b/fs/statfs.c index 2616424012ea7..59f33752c1311 100644 --- a/fs/statfs.c +++ b/fs/statfs.c @@ -29,6 +29,8 @@ static int flags_by_mnt(int mnt_flags) flags |= ST_NODIRATIME; if (mnt_flags & MNT_RELATIME) flags |= ST_RELATIME; + if (mnt_flags & MNT_NOSYMFOLLOW) + flags |= ST_NOSYMFOLLOW; return flags; } diff --git a/include/linux/mount.h b/include/linux/mount.h index de657bd211fa6..aaf343b38671c 100644 --- a/include/linux/mount.h +++ b/include/linux/mount.h @@ -30,6 +30,7 @@ struct fs_context; #define MNT_NODIRATIME 0x10 #define MNT_RELATIME 0x20 #define MNT_READONLY 0x40 /* does the user want this to be r/o? */ +#define MNT_NOSYMFOLLOW 0x80 #define MNT_SHRINKABLE 0x100 #define MNT_WRITE_HOLD 0x200 @@ -46,7 +47,7 @@ struct fs_context; #define MNT_SHARED_MASK (MNT_UNBINDABLE) #define MNT_USER_SETTABLE_MASK (MNT_NOSUID | MNT_NODEV | MNT_NOEXEC \ | MNT_NOATIME | MNT_NODIRATIME | MNT_RELATIME \ - | MNT_READONLY) + | MNT_READONLY | MNT_NOSYMFOLLOW) #define MNT_ATIME_MASK (MNT_NOATIME | MNT_NODIRATIME | MNT_RELATIME ) #define MNT_INTERNAL_FLAGS (MNT_SHARED | MNT_WRITE_HOLD | MNT_INTERNAL | \ diff --git a/include/linux/statfs.h b/include/linux/statfs.h index 9bc69edb8f188..fac4356ea1bfc 100644 --- a/include/linux/statfs.h +++ b/include/linux/statfs.h @@ -40,6 +40,7 @@ struct kstatfs { #define ST_NOATIME 0x0400 /* do not update access times */ #define ST_NODIRATIME 0x0800 /* do not update directory access times */ #define ST_RELATIME 0x1000 /* update atime relative to mtime/ctime */ +#define ST_NOSYMFOLLOW 0x2000 /* do not follow symlinks */ struct dentry; extern int vfs_get_fsid(struct dentry *dentry, __kernel_fsid_t *fsid); diff --git a/include/uapi/linux/mount.h b/include/uapi/linux/mount.h index 96a0240f23fed..dd8306ea336c1 100644 --- a/include/uapi/linux/mount.h +++ b/include/uapi/linux/mount.h @@ -16,6 +16,7 @@ #define MS_REMOUNT 32 /* Alter flags of a mounted FS */ #define MS_MANDLOCK 64 /* Allow mandatory locks on an FS */ #define MS_DIRSYNC 128 /* Directory modifications are synchronous */ +#define MS_NOSYMFOLLOW 256 /* Do not follow symlinks */ #define MS_NOATIME 1024 /* Do not update access times. */ #define MS_NODIRATIME 2048 /* Do not update directory access times */ #define MS_BIND 4096