From: Stefan Berger <stefanb@linux.vnet.ibm.com>
To: Stephen Smalley <sds@tycho.nsa.gov>,
ebiederm@xmission.com, containers@lists.linux-foundation.org
Cc: lkp@01.org, xiaolong.ye@intel.com, linux-kernel@vger.kernel.org,
zohar@linux.vnet.ibm.com, serge@hallyn.com, tycho@docker.com,
James.Bottomley@HansenPartnership.com,
christian.brauner@mailbox.org, vgoyal@redhat.com,
amir73il@gmail.com, linux-security-module@vger.kernel.org,
Paul Moore <paul@paul-moore.com>,
selinux@tycho.nsa.gov
Subject: Re: [PATCH 3/3] Enable security.selinux in user namespaces
Date: Fri, 23 Jun 2017 19:41:52 -0400 [thread overview]
Message-ID: <f477e588-a557-65ae-13db-8e8a87955b7f@linux.vnet.ibm.com> (raw)
In-Reply-To: <1498249800.2063.9.camel@tycho.nsa.gov>
On 06/23/2017 04:30 PM, Stephen Smalley wrote:
> On Thu, 2017-06-22 at 14:59 -0400, Stefan Berger wrote:
>> Before the current modifications, SELinux extended attributes were
>> visible inside the user namespace but changes in patch 1 hid them.
>> This patch enables security.selinux in user namespaces and allows
>> them to be written to in the same way as security.capability.
>>
>> Signed-off-by: Stefan Berger <stefanb@linux.vnet.ibm.com>
>> ---
>> fs/xattr.c | 1 +
>> 1 file changed, 1 insertion(+)
>>
>> diff --git a/fs/xattr.c b/fs/xattr.c
>> index 045be85..37686ee 100644
>> --- a/fs/xattr.c
>> +++ b/fs/xattr.c
>> @@ -138,6 +138,7 @@ xattr_permission(struct inode *inode, const char
>> *name, int mask)
>> */
>> static const char *const userns_xattrs[] = {
>> XATTR_NAME_CAPS,
>> + XATTR_NAME_SELINUX,
>> NULL
>> };
>>
> (cc SELinux maintainers, curiously omitted from these patches)
>
> I don't think this works for SELinux. You don't deal with actually
> supporting multiple security.selinux attributes within SELinux itself
> (and I'm not asking you to do so), and without such support, this can't
> operate as intended. With these patches applied, IIUC, a setxattr() of
> security.selinux within a userns will end up setting only security.seli
> nux@uid=1000 on disk, but will then tell SELinux to update its in-core
> security label to the new value (via security_inode_post_setxattr).
> Meanwhile, on a subsequent getxattr(), you'll call
> security_inode_getsecurity() with the security.selinux@uid=1000 name,
> which will always fail because SELinux doesn't know anything about your
> new scheme, and then you'll call the filesystem handler and returns its
> value, which is no longer connected in any way to the actual label
> being used by SELinux. Also, SELinux itself makes calls to
> __vfs_getxattr() and __vfs_setxattr_noperm(), and I don't think your
> name remapping is correct in those cases.
>
> You also can't hide security.selinux within user namespaces. Today
> userspace can get and set security.selinux attributes within user
> namespaces (if allowed by policy), and further can specify the label to
> use for new files via /proc/self/attr/fscreate, which unsurprisingly
> isn't addressed by your changes. Changing that would be a userspace
> break.
I modified the 1st patch now in such a way that only security.capability
is rewritten, security.selinux and all other ones remain untouched.
https://github.com/stefanberger/linux/commits/xattr_for_userns.v2
Stefan
next prev parent reply other threads:[~2017-06-23 23:42 UTC|newest]
Thread overview: 47+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-06-22 18:59 [PATCH 0/3] Enable namespaced file capabilities Stefan Berger
2017-06-22 18:59 ` [PATCH 1/3] xattr: Enable security.capability in user namespaces Stefan Berger
2017-06-24 21:02 ` kbuild test robot
2017-06-24 21:02 ` [PATCH] xattr: fix kstrdup.cocci warnings kbuild test robot
2017-06-22 18:59 ` [PATCH 2/3] Enable capabilities of files from shared filesystem Stefan Berger
2017-06-22 18:59 ` [PATCH 3/3] Enable security.selinux in user namespaces Stefan Berger
2017-06-23 20:30 ` Stephen Smalley
2017-06-23 23:41 ` Stefan Berger [this message]
2017-06-22 19:59 ` [PATCH 0/3] Enable namespaced file capabilities Casey Schaufler
2017-06-22 20:12 ` Stefan Berger
2017-06-22 20:33 ` Casey Schaufler
2017-06-22 21:03 ` Stefan Berger
2017-06-22 21:09 ` Serge E. Hallyn
2017-06-22 22:40 ` Casey Schaufler
2017-06-22 23:07 ` Serge E. Hallyn
2017-06-22 23:29 ` James Bottomley
2017-06-22 23:32 ` Serge E. Hallyn
2017-06-22 23:36 ` Serge E. Hallyn
2017-06-23 0:13 ` James Bottomley
2017-06-23 1:19 ` Serge E. Hallyn
2017-06-23 17:37 ` Eric W. Biederman
2017-06-23 18:39 ` Serge E. Hallyn
2017-06-23 7:01 ` Amir Goldstein
2017-06-23 16:00 ` Serge E. Hallyn
2017-06-23 16:16 ` Casey Schaufler
2017-06-23 16:30 ` Serge E. Hallyn
2017-06-23 16:53 ` Casey Schaufler
2017-06-23 17:01 ` Serge E. Hallyn
2017-06-23 17:49 ` Eric W. Biederman
2017-06-23 18:32 ` Serge E. Hallyn
2017-06-23 17:07 ` James Bottomley
2017-06-23 17:20 ` Serge E. Hallyn
2017-06-23 17:38 ` Stefan Berger
2017-06-23 18:34 ` Serge E. Hallyn
2017-06-23 18:08 ` Stefan Berger
2017-06-23 18:35 ` Serge E. Hallyn
2017-06-23 20:30 ` Casey Schaufler
2017-06-23 23:09 ` Stefan Berger
2017-06-23 23:51 ` Casey Schaufler
2017-06-28 5:41 ` Serge E. Hallyn
2017-06-28 7:18 ` Amir Goldstein
2017-06-28 14:04 ` Stefan Berger
2017-06-28 14:28 ` Serge E. Hallyn
2017-06-23 20:09 ` Vivek Goyal
2017-06-23 20:17 ` Serge E. Hallyn
2017-06-23 20:36 ` Vivek Goyal
2017-06-23 20:51 ` Serge E. Hallyn
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