Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S941129AbcJXOKF (ORCPT ); Mon, 24 Oct 2016 10:10:05 -0400 Received: from mail-ua0-f179.google.com ([209.85.217.179]:36657 "EHLO mail-ua0-f179.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S940767AbcJXOJx (ORCPT ); Mon, 24 Oct 2016 10:09:53 -0400 MIME-Version: 1.0 In-Reply-To: <1476880312-64786-1-git-send-email-mnissler@chromium.org> References: <1476880312-64786-1-git-send-email-mnissler@chromium.org> From: Mattias Nissler Date: Mon, 24 Oct 2016 16:09:31 +0200 X-Google-Sender-Auth: PLN4zsPr2CeuPx08btKgyjBGcIc Message-ID: Subject: Re: [PATCH v2] Add a "nosymlinks" mount option. To: linux-fsdevel@vger.kernel.org Cc: Alexander Viro , linux-kernel@vger.kernel.org, Colin Walters , "Austin S . Hemmelgarn" Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 6065 Lines: 143 Friendly ping - does this version of the patch have any chance on getting included in mainline? On Wed, Oct 19, 2016 at 2:31 PM, Mattias Nissler wrote: > For mounts that have the new "nosymlinks" option, don't follow > symlinks when resolving paths. The new option is similar in spirit to > the existing "nodev", "noexec", and "nosuid" options. > > Note that symlinks may still be created on mounts where the > "nosymlinks" option is present. readlink() remains functional, so user > space code that is aware of symlinks can still choose to follow them > explicitly. > > Setting the "nosymlinks" mount option helps prevent privileged writers > from modifying files unintentionally in case there is an unexpected > link along the accessed path. The "nosymlinks" option is thus useful > as a defensive measure for systems that need to deal with untrusted > file systems in privileged contexts. > > Signed-off-by: Mattias Nissler > --- > fs/namei.c | 3 +++ > fs/namespace.c | 9 ++++++--- > fs/proc_namespace.c | 1 + > fs/statfs.c | 2 ++ > include/linux/mount.h | 3 ++- > include/linux/statfs.h | 1 + > include/uapi/linux/fs.h | 1 + > 7 files changed, 16 insertions(+), 4 deletions(-) > > diff --git a/fs/namei.c b/fs/namei.c > index 5b4eed2..4cddcf3 100644 > --- a/fs/namei.c > +++ b/fs/namei.c > @@ -1021,6 +1021,9 @@ const char *get_link(struct nameidata *nd) > touch_atime(&last->link); > } > > + if (nd->path.mnt->mnt_flags & MNT_NOSYMLINKS) > + return ERR_PTR(-EACCES); > + > error = security_inode_follow_link(dentry, inode, > nd->flags & LOOKUP_RCU); > if (unlikely(error)) > diff --git a/fs/namespace.c b/fs/namespace.c > index e6c234b..deec84e 100644 > --- a/fs/namespace.c > +++ b/fs/namespace.c > @@ -2732,6 +2732,8 @@ long do_mount(const char *dev_name, const char __user *dir_name, > mnt_flags &= ~(MNT_RELATIME | MNT_NOATIME); > if (flags & MS_RDONLY) > mnt_flags |= MNT_READONLY; > + if (flags & MS_NOSYMLINKS) > + mnt_flags |= MNT_NOSYMLINKS; > > /* The default atime for remount is preservation */ > if ((flags & MS_REMOUNT) && > @@ -2741,9 +2743,10 @@ long do_mount(const char *dev_name, const char __user *dir_name, > mnt_flags |= path.mnt->mnt_flags & MNT_ATIME_MASK; > } > > - flags &= ~(MS_NOSUID | MS_NOEXEC | MS_NODEV | MS_ACTIVE | MS_BORN | > - MS_NOATIME | MS_NODIRATIME | MS_RELATIME| MS_KERNMOUNT | > - MS_STRICTATIME | MS_NOREMOTELOCK); > + flags &= ~(MS_NOSUID | MS_NOEXEC | MS_NODEV | MS_NOSYMLINKS | > + MS_ACTIVE | MS_BORN | MS_NOATIME | MS_NODIRATIME | > + MS_RELATIME | MS_KERNMOUNT | MS_STRICTATIME | > + MS_NOREMOTELOCK); > > if (flags & MS_REMOUNT) > retval = do_remount(&path, flags & ~MS_REMOUNT, mnt_flags, > diff --git a/fs/proc_namespace.c b/fs/proc_namespace.c > index 3f1190d..a1949d9 100644 > --- a/fs/proc_namespace.c > +++ b/fs/proc_namespace.c > @@ -67,6 +67,7 @@ static void show_mnt_opts(struct seq_file *m, struct vfsmount *mnt) > { MNT_NOATIME, ",noatime" }, > { MNT_NODIRATIME, ",nodiratime" }, > { MNT_RELATIME, ",relatime" }, > + { MNT_NOSYMLINKS, ",nosymlinks" }, > { 0, NULL } > }; > const struct proc_fs_info *fs_infop; > diff --git a/fs/statfs.c b/fs/statfs.c > index 083dc0a..7ff7c32 100644 > --- a/fs/statfs.c > +++ b/fs/statfs.c > @@ -27,6 +27,8 @@ static int flags_by_mnt(int mnt_flags) > flags |= ST_NODIRATIME; > if (mnt_flags & MNT_RELATIME) > flags |= ST_RELATIME; > + if (mnt_flags & MNT_NOSYMLINKS) > + flags |= ST_NOSYMLINKS; > return flags; > } > > diff --git a/include/linux/mount.h b/include/linux/mount.h > index 1172cce..5e302f4 100644 > --- a/include/linux/mount.h > +++ b/include/linux/mount.h > @@ -28,6 +28,7 @@ struct mnt_namespace; > #define MNT_NODIRATIME 0x10 > #define MNT_RELATIME 0x20 > #define MNT_READONLY 0x40 /* does the user want this to be r/o? */ > +#define MNT_NOSYMLINKS 0x80 > > #define MNT_SHRINKABLE 0x100 > #define MNT_WRITE_HOLD 0x200 > @@ -44,7 +45,7 @@ struct mnt_namespace; > #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_NOSYMLINKS) > #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 0166d32..994b059 100644 > --- a/include/linux/statfs.h > +++ b/include/linux/statfs.h > @@ -39,5 +39,6 @@ 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_NOSYMLINKS 0x2000 /* do not follow symbolic links */ > > #endif > diff --git a/include/uapi/linux/fs.h b/include/uapi/linux/fs.h > index acb2b61..06193d8 100644 > --- a/include/uapi/linux/fs.h > +++ b/include/uapi/linux/fs.h > @@ -130,6 +130,7 @@ struct inodes_stat_t { > #define MS_I_VERSION (1<<23) /* Update inode I_version field */ > #define MS_STRICTATIME (1<<24) /* Always perform atime updates */ > #define MS_LAZYTIME (1<<25) /* Update the on-disk [acm]times lazily */ > +#define MS_NOSYMLINKS (1<<26) /* Do not follow symbolic links */ > > /* These sb flags are internal to the kernel */ > #define MS_NOREMOTELOCK (1<<27) > -- > 2.8.0.rc3.226.g39d4020 >