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From: "Eric W. Biederman" <ebiederm-aS9lmoZGLiVWk0Htik3J/w@public.gmane.org>
To: Linux Containers
	<containers-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org>
Cc: Miklos Szeredi <miklos-sUDqSbJrdHQHWmgEVkV9KA@public.gmane.org>,
	Andy Lutomirski <luto-kltTT9wpgjJwATOyAt5JVQ@public.gmane.org>,
	James Bottomley
	<James.Bottomley-d9PhHud1JfjCXq6kfMZ53/egYHeGw8Jk@public.gmane.org>,
	Seth Forshee
	<seth.forshee-Z7WLFzj8eWMS+FvcfC7Uqw@public.gmane.org>,
	linux-fsdevel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
	Djalal Harouni <tixxdz-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
Subject: [PATCH review 01/13] mnt: Account for MS_RDONLY in fs_fully_visible
Date: Mon, 20 Jun 2016 12:21:18 -0500	[thread overview]
Message-ID: <20160620172130.15712-1-ebiederm@xmission.com> (raw)
In-Reply-To: <87fus77pns.fsf-JOvCrm2gF+uungPnsOpG7nhyD016LWXt@public.gmane.org>

In rare cases it is possible for s_flags & MS_RDONLY to be set but
MNT_READONLY to be clear.  This starting combination can cause
fs_fully_visible to fail to ensure that the new mount is readonly.
Therefore force MNT_LOCK_READONLY in the new mount if MS_RDONLY
is set on the source filesystem of the mount.

In general both MS_RDONLY and MNT_READONLY are set at the same for
mounts so I don't expect any programs to care.  Nor do I expect
MS_RDONLY to be set on proc or sysfs in the initial user namespace,
which further decreases the likelyhood of problems.

Which means this change should only affect system configurations by
paranoid sysadmins who should welcome the additional protection
as it keeps people from wriggling out of their policies.

Cc: stable-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
Fixes: 8c6cf9cc829f ("mnt: Modify fs_fully_visible to deal with locked ro nodev and atime")
Signed-off-by: "Eric W. Biederman" <ebiederm-aS9lmoZGLiVWk0Htik3J/w@public.gmane.org>
---
 fs/namespace.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/fs/namespace.c b/fs/namespace.c
index a7ec92c051f5..783004af5707 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -3247,6 +3247,10 @@ static bool fs_fully_visible(struct file_system_type *type, int *new_mnt_flags)
 		if (mnt->mnt.mnt_sb->s_iflags & SB_I_NOEXEC)
 			mnt_flags &= ~(MNT_LOCK_NOSUID | MNT_LOCK_NOEXEC);
 
+		/* Don't miss readonly hidden in the superblock flags */
+		if (mnt->mnt.mnt_sb->s_flags & MS_RDONLY)
+			mnt_flags |= MNT_LOCK_READONLY;
+
 		/* Verify the mount flags are equal to or more permissive
 		 * than the proposed new mount.
 		 */
-- 
2.8.3

WARNING: multiple messages have this Message-ID (diff)
From: "Eric W. Biederman" <ebiederm@xmission.com>
To: Linux Containers <containers@lists.linux-foundation.org>
Cc: linux-fsdevel@vger.kernel.org, Miklos Szeredi <miklos@szeredi.hu>,
	James Bottomley <James.Bottomley@HansenPartnership.com>,
	Djalal Harouni <tixxdz@gmail.com>,
	Seth Forshee <seth.forshee@canonical.com>,
	"Serge E. Hallyn" <serge@hallyn.com>,
	Andy Lutomirski <luto@amacapital.net>
Subject: [PATCH review 01/13] mnt: Account for MS_RDONLY in fs_fully_visible
Date: Mon, 20 Jun 2016 12:21:18 -0500	[thread overview]
Message-ID: <20160620172130.15712-1-ebiederm@xmission.com> (raw)
In-Reply-To: <87fus77pns.fsf@x220.int.ebiederm.org>

In rare cases it is possible for s_flags & MS_RDONLY to be set but
MNT_READONLY to be clear.  This starting combination can cause
fs_fully_visible to fail to ensure that the new mount is readonly.
Therefore force MNT_LOCK_READONLY in the new mount if MS_RDONLY
is set on the source filesystem of the mount.

In general both MS_RDONLY and MNT_READONLY are set at the same for
mounts so I don't expect any programs to care.  Nor do I expect
MS_RDONLY to be set on proc or sysfs in the initial user namespace,
which further decreases the likelyhood of problems.

Which means this change should only affect system configurations by
paranoid sysadmins who should welcome the additional protection
as it keeps people from wriggling out of their policies.

Cc: stable@vger.kernel.org
Fixes: 8c6cf9cc829f ("mnt: Modify fs_fully_visible to deal with locked ro nodev and atime")
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
---
 fs/namespace.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/fs/namespace.c b/fs/namespace.c
index a7ec92c051f5..783004af5707 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -3247,6 +3247,10 @@ static bool fs_fully_visible(struct file_system_type *type, int *new_mnt_flags)
 		if (mnt->mnt.mnt_sb->s_iflags & SB_I_NOEXEC)
 			mnt_flags &= ~(MNT_LOCK_NOSUID | MNT_LOCK_NOEXEC);
 
+		/* Don't miss readonly hidden in the superblock flags */
+		if (mnt->mnt.mnt_sb->s_flags & MS_RDONLY)
+			mnt_flags |= MNT_LOCK_READONLY;
+
 		/* Verify the mount flags are equal to or more permissive
 		 * than the proposed new mount.
 		 */
-- 
2.8.3


  parent reply	other threads:[~2016-06-20 17:21 UTC|newest]

Thread overview: 56+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-06-20 17:09 [PATCH review 0/13] Adding a userns owner to struct super_block Eric W. Biederman
2016-06-20 17:09 ` Eric W. Biederman
     [not found] ` <87fus77pns.fsf-JOvCrm2gF+uungPnsOpG7nhyD016LWXt@public.gmane.org>
2016-06-20 17:21   ` Eric W. Biederman [this message]
2016-06-20 17:21     ` [PATCH review 01/13] mnt: Account for MS_RDONLY in fs_fully_visible Eric W. Biederman
     [not found]     ` <20160620172130.15712-1-ebiederm-aS9lmoZGLiVWk0Htik3J/w@public.gmane.org>
2016-06-20 17:21       ` [PATCH review 02/13] mnt: Refactor fs_fully_visible into mount_too_revealing Eric W. Biederman
2016-06-20 17:21         ` Eric W. Biederman
     [not found]         ` <20160620172130.15712-2-ebiederm-aS9lmoZGLiVWk0Htik3J/w@public.gmane.org>
2016-06-20 22:53           ` Andy Lutomirski
2016-06-20 22:53             ` Andy Lutomirski
     [not found]             ` <CALCETrXv2aeP38AmUaRVMC+O-oeWKwDcy8fPfsOCu1f8mncZEA-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2016-06-21 18:54               ` Eric W. Biederman
2016-06-21 18:54                 ` Eric W. Biederman
     [not found]                 ` <874m8m4bky.fsf-JOvCrm2gF+uungPnsOpG7nhyD016LWXt@public.gmane.org>
2016-06-23 21:23                   ` Djalal Harouni
2016-06-23 21:23                     ` Djalal Harouni
2016-06-24  6:56                   ` Serge E. Hallyn
2016-06-24  6:56                 ` Serge E. Hallyn
2016-06-22 19:40           ` Seth Forshee
2016-06-22 19:40             ` Seth Forshee
2016-06-20 17:21       ` [PATCH review 03/13] ipc: Initialize ipc_namespace->user_ns early Eric W. Biederman
2016-06-20 17:21         ` Eric W. Biederman
     [not found]         ` <20160620172130.15712-3-ebiederm-aS9lmoZGLiVWk0Htik3J/w@public.gmane.org>
2016-06-24 14:34           ` Djalal Harouni
2016-06-24 14:34             ` Djalal Harouni
2016-06-20 17:21       ` [PATCH review 04/13] vfs: Pass data, ns, and ns->userns to mount_ns Eric W. Biederman
2016-06-20 17:21         ` Eric W. Biederman
2016-06-20 17:21       ` [PATCH review 05/13] proc: Convert proc_mount to use mount_ns Eric W. Biederman
2016-06-20 17:21         ` Eric W. Biederman
     [not found]         ` <20160620172130.15712-5-ebiederm-aS9lmoZGLiVWk0Htik3J/w@public.gmane.org>
2016-06-23 11:50           ` Djalal Harouni
2016-06-23 11:50         ` Djalal Harouni
2016-06-20 17:21       ` [PATCH review 06/13] fs: Add user namespace member to struct super_block Eric W. Biederman
2016-06-20 17:21         ` Eric W. Biederman
2016-06-20 17:21       ` [PATCH review 07/13] mnt: Move the FS_USERNS_MOUNT check into sget_userns Eric W. Biederman
2016-06-20 17:21         ` Eric W. Biederman
     [not found]         ` <20160620172130.15712-7-ebiederm-aS9lmoZGLiVWk0Htik3J/w@public.gmane.org>
2016-06-22 19:43           ` Seth Forshee
2016-06-22 19:43             ` Seth Forshee
2016-06-20 17:21       ` [PATCH review 08/13] kernfs: The cgroup filesystem also benefits from SB_I_NOEXEC Eric W. Biederman
2016-06-20 17:21         ` Eric W. Biederman
2016-06-20 17:21       ` [PATCH review 09/13] ipc/mqueue: The mqueue filesystem should never contain executables Eric W. Biederman
2016-06-20 17:21         ` Eric W. Biederman
2016-06-20 17:21       ` [PATCH review 10/13] vfs: Generalize filesystem nodev handling Eric W. Biederman
2016-06-20 17:21         ` Eric W. Biederman
     [not found]         ` <20160620172130.15712-10-ebiederm-aS9lmoZGLiVWk0Htik3J/w@public.gmane.org>
2016-06-20 22:57           ` Andy Lutomirski
2016-06-20 22:57             ` Andy Lutomirski
     [not found]             ` <CALCETrUWsnRgjyRyb+_0u0PYubx9gg=hUAso=073yjJY+m205g-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2016-06-21 19:09               ` Eric W. Biederman
2016-06-21 19:09                 ` Eric W. Biederman
2016-06-20 17:21       ` [PATCH review 11/13] mnt: Simplify mount_too_revealing Eric W. Biederman
2016-06-20 17:21         ` Eric W. Biederman
     [not found]         ` <20160620172130.15712-11-ebiederm-aS9lmoZGLiVWk0Htik3J/w@public.gmane.org>
2016-06-22 19:48           ` Seth Forshee
2016-06-22 19:48             ` Seth Forshee
2016-06-20 17:21       ` [PATCH review 12/13] userns: Remove implicit MNT_NODEV fragility Eric W. Biederman
2016-06-20 17:21         ` Eric W. Biederman
2016-06-22 19:49         ` Seth Forshee
     [not found]         ` <20160620172130.15712-12-ebiederm-aS9lmoZGLiVWk0Htik3J/w@public.gmane.org>
2016-06-20 22:58           ` Andy Lutomirski
2016-06-20 22:58             ` Andy Lutomirski
2016-06-22 19:49           ` Seth Forshee
2016-06-20 17:21       ` [PATCH review 13/13] userns: Remove the now unnecessary FS_USERNS_DEV_MOUNT flag Eric W. Biederman
2016-06-20 17:21         ` Eric W. Biederman
2016-06-22 19:50         ` Seth Forshee
     [not found]         ` <20160620172130.15712-13-ebiederm-aS9lmoZGLiVWk0Htik3J/w@public.gmane.org>
2016-06-22 19:50           ` Seth Forshee

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