MLS directory label inheritance rules

MLS directory label inheritance rules

[Nick Kralevich]

When a file is created in a directory, the default label for the file
is based on the label of the enclosing directory (unless something
like setfscreatecon is used). For example:

bullhead:/ # cd /data/misc/zoneinfo/

bullhead:/data/misc/zoneinfo # ls -ladZ .
drwxrwxr-x 2 system system u:object_r:zoneinfo_data_file:s0 4096
1971-06-19 17:07 .
bullhead:/data/misc/zoneinfo # touch asdf
bullhead:/data/misc/zoneinfo # ls -ladZ . asdf

drwxrwxr-x 2 system system u:object_r:zoneinfo_data_file:s0 4096
2017-04-07 18:32 .
-rw-rw-rw- 1 root   root   u:object_r:zoneinfo_data_file:s0    0
2017-04-07 18:32 asdf

note how the label of the "asdf" file matches the label of the
enclosing directory.

However, that's not true when the directory uses categories. In that
case, the newly created file inherits the label, but not the
categories. For example:

bullhead:/data/data # cd /data/data/com.android.chrome
bullhead:/data/data/com.android.chrome # ls -ladZ .
drwx------ 6 u0_a60 u0_a60 u:object_r:app_data_file:s0:c512,c768 4096
1971-07-15 15:31 .
bullhead:/data/data/com.android.chrome # touch asdf
bullhead:/data/data/com.android.chrome # ls -laZd . asdf
drwx------ 6 u0_a60 u0_a60 u:object_r:app_data_file:s0:c512,c768 4096
2017-04-07 18:35 .
-rw-rw-rw- 1 root   root   u:object_r:app_data_file:s0              0
2017-04-07 18:35 asdf

Note how the label is maintained, but the "c512,c768" portion is not
maintained. While this example occurs when I'm running in a permissive
domain, it also occurs in an enforcing domain.

The inconsistency seems weird, and I'm sure there's a good reason why
this occurs that I'm not familiar with. Can someone help me understand
if this is expected, and if so, why?

-- 
Nick Kralevich | Android Security | nnk@google.com | 650.214.4037

Re: MLS directory label inheritance rules

[William Roberts]

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On Apr 7, 2017 11:41, "Nick Kralevich" <nnk@google.com> wrote:

When a file is created in a directory, the default label for the file
is based on the label of the enclosing directory (unless something
like setfscreatecon is used). For example:

bullhead:/ # cd /data/misc/zoneinfo/

bullhead:/data/misc/zoneinfo # ls -ladZ .
drwxrwxr-x 2 system system u:object_r:zoneinfo_data_file:s0 4096
1971-06-19 17:07 .
bullhead:/data/misc/zoneinfo # touch asdf
bullhead:/data/misc/zoneinfo # ls -ladZ . asdf

drwxrwxr-x 2 system system u:object_r:zoneinfo_data_file:s0 4096
2017-04-07 18:32 .
-rw-rw-rw- 1 root   root   u:object_r:zoneinfo_data_file:s0    0
2017-04-07 18:32 asdf

note how the label of the "asdf" file matches the label of the
enclosing directory.

However, that's not true when the directory uses categories. In that
case, the newly created file inherits the label, but not the
categories. For example:

bullhead:/data/data # cd /data/data/com.android.chrome
bullhead:/data/data/com.android.chrome # ls -ladZ .
drwx------ 6 u0_a60 u0_a60 u:object_r:app_data_file:s0:c512,c768 4096
1971-07-15 15:31 .
bullhead:/data/data/com.android.chrome # touch asdf
bullhead:/data/data/com.android.chrome # ls -laZd . asdf
drwx------ 6 u0_a60 u0_a60 u:object_r:app_data_file:s0:c512,c768 4096
2017-04-07 18:35 .
-rw-rw-rw- 1 root   root   u:object_r:app_data_file:s0              0
2017-04-07 18:35 asdf

Note how the label is maintained, but the "c512,c768" portion is not
maintained. While this example occurs when I'm running in a permissive
domain, it also occurs in an enforcing domain.

The inconsistency seems weird, and I'm sure there's a good reason why
this occurs that I'm not familiar with. Can someone help me understand
if this is expected, and if so, why?


If you write top secret data it should stay top secret even if you're
writing to a folder that is normally reserved for secret data, or perhaps
mixed data. Iirc it uses the MLS of the process when creating the file
entry.


--
Nick Kralevich | Android Security | nnk@google.com | 650.214.4037
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Re: MLS directory label inheritance rules

[Dominick Grift]

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On Fri, Apr 07, 2017 at 11:39:55AM -0700, Nick Kralevich wrote:
> When a file is created in a directory, the default label for the file
> is based on the label of the enclosing directory (unless something
> like setfscreatecon is used). For example:
> 
> bullhead:/ # cd /data/misc/zoneinfo/
> 
> bullhead:/data/misc/zoneinfo # ls -ladZ .
> drwxrwxr-x 2 system system u:object_r:zoneinfo_data_file:s0 4096
> 1971-06-19 17:07 .
> bullhead:/data/misc/zoneinfo # touch asdf
> bullhead:/data/misc/zoneinfo # ls -ladZ . asdf
> 
> drwxrwxr-x 2 system system u:object_r:zoneinfo_data_file:s0 4096
> 2017-04-07 18:32 .
> -rw-rw-rw- 1 root   root   u:object_r:zoneinfo_data_file:s0    0
> 2017-04-07 18:32 asdf
> 
> note how the label of the "asdf" file matches the label of the
> enclosing directory.
> 
> However, that's not true when the directory uses categories. In that
> case, the newly created file inherits the label, but not the
> categories. For example:
> 
> bullhead:/data/data # cd /data/data/com.android.chrome
> bullhead:/data/data/com.android.chrome # ls -ladZ .
> drwx------ 6 u0_a60 u0_a60 u:object_r:app_data_file:s0:c512,c768 4096
> 1971-07-15 15:31 .
> bullhead:/data/data/com.android.chrome # touch asdf
> bullhead:/data/data/com.android.chrome # ls -laZd . asdf
> drwx------ 6 u0_a60 u0_a60 u:object_r:app_data_file:s0:c512,c768 4096
> 2017-04-07 18:35 .
> -rw-rw-rw- 1 root   root   u:object_r:app_data_file:s0              0
> 2017-04-07 18:35 asdf
> 
> Note how the label is maintained, but the "c512,c768" portion is not
> maintained. While this example occurs when I'm running in a permissive
> domain, it also occurs in an enforcing domain.
> 
> The inconsistency seems weird, and I'm sure there's a good reason why
> this occurs that I'm not familiar with. Can someone help me understand
> if this is expected, and if so, why?

I think that is actually a sane default (defaultrange source) as opposed to default range target because if a process associated with s0:c123,c456 creates a file, then i would expect that file to inherit s0:c123,c456 from the source and not s0 from the target for example

RedHat, i think, overrides this default as well and uses defaultrange target and I think that is a strange decision.

If I have qemu instance with s0:c123,c456 that for example creates a pty, then I would want to have that pty constrained by s0:c123,c456 as well

> 
> -- 
> Nick Kralevich | Android Security | nnk@google.com | 650.214.4037
> _______________________________________________
> Selinux mailing list
> Selinux@tycho.nsa.gov
> To unsubscribe, send email to Selinux-leave@tycho.nsa.gov.
> To get help, send an email containing "help" to Selinux-request@tycho.nsa.gov.

-- 
Key fingerprint = 5F4D 3CDB D3F8 3652 FBD8  02D5 3B6C 5F1D 2C7B 6B02
https://sks-keyservers.net/pks/lookup?op=get&search=0x3B6C5F1D2C7B6B02
Dominick Grift

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Re: MLS directory label inheritance rules

[Stephen Smalley]

On Fri, 2017-04-07 at 11:39 -0700, Nick Kralevich wrote:
> When a file is created in a directory, the default label for the file
> is based on the label of the enclosing directory (unless something
> like setfscreatecon is used). For example:
> 
> bullhead:/ # cd /data/misc/zoneinfo/
> 
> bullhead:/data/misc/zoneinfo # ls -ladZ .
> drwxrwxr-x 2 system system u:object_r:zoneinfo_data_file:s0 4096
> 1971-06-19 17:07 .
> bullhead:/data/misc/zoneinfo # touch asdf
> bullhead:/data/misc/zoneinfo # ls -ladZ . asdf
> 
> drwxrwxr-x 2 system system u:object_r:zoneinfo_data_file:s0 4096
> 2017-04-07 18:32 .
> -rw-rw-rw- 1 root   root   u:object_r:zoneinfo_data_file:s0    0
> 2017-04-07 18:32 asdf
> 
> note how the label of the "asdf" file matches the label of the
> enclosing directory.
> 
> However, that's not true when the directory uses categories. In that
> case, the newly created file inherits the label, but not the
> categories. For example:
> 
> bullhead:/data/data # cd /data/data/com.android.chrome
> bullhead:/data/data/com.android.chrome # ls -ladZ .
> drwx------ 6 u0_a60 u0_a60 u:object_r:app_data_file:s0:c512,c768 4096
> 1971-07-15 15:31 .
> bullhead:/data/data/com.android.chrome # touch asdf
> bullhead:/data/data/com.android.chrome # ls -laZd . asdf
> drwx------ 6 u0_a60 u0_a60 u:object_r:app_data_file:s0:c512,c768 4096
> 2017-04-07 18:35 .
> -rw-rw-rw- 1 root   root   u:object_r:app_data_file:s0              0
> 2017-04-07 18:35 asdf
> 
> Note how the label is maintained, but the "c512,c768" portion is not
> maintained. While this example occurs when I'm running in a
> permissive
> domain, it also occurs in an enforcing domain.
> 
> The inconsistency seems weird, and I'm sure there's a good reason why
> this occurs that I'm not familiar with. Can someone help me
> understand
> if this is expected, and if so, why?

First, the good news is that you get to specify which behavior you want
for each context field and object class through policy (as long as your
kernel and policy version supports it), see:
https://selinuxproject.org/page/DefaultRules

Second, there are different defaults for each of the fields of the
security contexts based on what is most normative for that particular
security model.  The user identity defaults to that of the creating
process since we typically do not allow a process to create files with
a different user identity and want the file to reflect its creator
(this is defined through constraints on user identity in policies that
define more than one, unlike Android). The role defaults to the fixed
object_r role because originally we didn't envision a use case for
roles on files.  The MLS range defaults to the low/current level of the
process because a process is typically not allowed to create files at a
different level and we want the file to reflect the sensitivity of the
data which originated from the process. The type defaults to a related
object type (in this case that of the parent directory) because process
domains and object types are separate (aside from overlapping use for
/proc/pid) and the relationships among them are explicit through the TE
rules / access matrix rather than through implicit rules.

Of course, in addition to being able to globally configure the default
behavior, you can also customize specific cases through the
role/type/range_transition rules.

With your example above, you wanted the file to inherit the level of
the directory, but consider the situation where a process with
categories (:s0:c512,c768) creates a file in some shared
(mlstrustedobject) directory that is just :s0.  Do you want that file
to end up as just :s0?  In the MLS world, that would be a downgrade /
info leak.

Re: MLS directory label inheritance rules

[Stephen Smalley]

On Fri, 2017-04-07 at 15:41 -0400, Stephen Smalley wrote:
> On Fri, 2017-04-07 at 11:39 -0700, Nick Kralevich wrote:
> > When a file is created in a directory, the default label for the
> > file
> > is based on the label of the enclosing directory (unless something
> > like setfscreatecon is used). For example:
> > 
> > bullhead:/ # cd /data/misc/zoneinfo/
> > 
> > bullhead:/data/misc/zoneinfo # ls -ladZ .
> > drwxrwxr-x 2 system system u:object_r:zoneinfo_data_file:s0 4096
> > 1971-06-19 17:07 .
> > bullhead:/data/misc/zoneinfo # touch asdf
> > bullhead:/data/misc/zoneinfo # ls -ladZ . asdf
> > 
> > drwxrwxr-x 2 system system u:object_r:zoneinfo_data_file:s0 4096
> > 2017-04-07 18:32 .
> > -rw-rw-rw- 1 root   root   u:object_r:zoneinfo_data_file:s0    0
> > 2017-04-07 18:32 asdf
> > 
> > note how the label of the "asdf" file matches the label of the
> > enclosing directory.
> > 
> > However, that's not true when the directory uses categories. In
> > that
> > case, the newly created file inherits the label, but not the
> > categories. For example:
> > 
> > bullhead:/data/data # cd /data/data/com.android.chrome
> > bullhead:/data/data/com.android.chrome # ls -ladZ .
> > drwx------ 6 u0_a60 u0_a60 u:object_r:app_data_file:s0:c512,c768
> > 4096
> > 1971-07-15 15:31 .
> > bullhead:/data/data/com.android.chrome # touch asdf
> > bullhead:/data/data/com.android.chrome # ls -laZd . asdf
> > drwx------ 6 u0_a60 u0_a60 u:object_r:app_data_file:s0:c512,c768
> > 4096
> > 2017-04-07 18:35 .
> > -rw-rw-rw- 1
> > root   root   u:object_r:app_data_file:s0              0
> > 2017-04-07 18:35 asdf
> > 
> > Note how the label is maintained, but the "c512,c768" portion is
> > not
> > maintained. While this example occurs when I'm running in a
> > permissive
> > domain, it also occurs in an enforcing domain.
> > 
> > The inconsistency seems weird, and I'm sure there's a good reason
> > why
> > this occurs that I'm not familiar with. Can someone help me
> > understand
> > if this is expected, and if so, why?
> 
> First, the good news is that you get to specify which behavior you
> want
> for each context field and object class through policy (as long as
> your
> kernel and policy version supports it), see:
> https://selinuxproject.org/page/DefaultRules
> 
> Second, there are different defaults for each of the fields of the
> security contexts based on what is most normative for that particular
> security model.  The user identity defaults to that of the creating
> process since we typically do not allow a process to create files
> with
> a different user identity and want the file to reflect its creator
> (this is defined through constraints on user identity in policies
> that
> define more than one, unlike Android). The role defaults to the fixed
> object_r role because originally we didn't envision a use case for
> roles on files.  The MLS range defaults to the low/current level of
> the
> process because a process is typically not allowed to create files at
> a
> different level and we want the file to reflect the sensitivity of
> the
> data which originated from the process. The type defaults to a
> related
> object type (in this case that of the parent directory) because
> process
> domains and object types are separate (aside from overlapping use for
> /proc/pid) and the relationships among them are explicit through the
> TE
> rules / access matrix rather than through implicit rules.
> 
> Of course, in addition to being able to globally configure the
> default
> behavior, you can also customize specific cases through the
> role/type/range_transition rules.
> 
> With your example above, you wanted the file to inherit the level of
> the directory, but consider the situation where a process with
> categories (:s0:c512,c768) creates a file in some shared
> (mlstrustedobject) directory that is just :s0.  Do you want that file
> to end up as just :s0?  In the MLS world, that would be a downgrade /
> info leak.

I guess that's not a great example since then the file would also end
up with the same type by default and thus would be a mlstrustedobject
and accessible regardless of its level.  So you'd want a type
transition to a derived type for files created in that directory to
avoid that.

Re: MLS directory label inheritance rules

[Dennis Sherrell]

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In a thread ending with Nick Kravelich's contact infirmation, it was
written:

"
If you write top secret data it should stay top secret even if you're
writing to a folder that is normally reserved for secret data, or perhaps
mixed data. Iirc it uses the MLS of the process when creating the file
entry."

I disagree. Top Secret data shoud not be written to a folder which was not
provisioned for such. Allowing persons or processess of lower
classification access to "containers" with higher clearance requirements
could cause a data spill. Any thoughts as to active handling of such?

Dennis Sherrell
Sherrell Consulting
Bakersfield, California Company #136601
Counter-Terrorism
Cybernetic Countermeasure Developer

On Fri, Apr 7, 2017, 12:55 PM Stephen Smalley <sds@tycho.nsa.gov> wrote:

> On Fri, 2017-04-07 at 15:41 -0400, Stephen Smalley wrote:
> > On Fri, 2017-04-07 at 11:39 -0700, Nick Kralevich wrote:
> > > When a file is created in a directory, the default label for the
> > > file
> > > is based on the label of the enclosing directory (unless something
> > > like setfscreatecon is used). For example:
> > >
> > > bullhead:/ # cd /data/misc/zoneinfo/
> > >
> > > bullhead:/data/misc/zoneinfo # ls -ladZ .
> > > drwxrwxr-x 2 system system u:object_r:zoneinfo_data_file:s0 4096
> > > 1971-06-19 17:07 .
> > > bullhead:/data/misc/zoneinfo # touch asdf
> > > bullhead:/data/misc/zoneinfo # ls -ladZ . asdf
> > >
> > > drwxrwxr-x 2 system system u:object_r:zoneinfo_data_file:s0 4096
> > > 2017-04-07 18:32 .
> > > -rw-rw-rw- 1 root   root   u:object_r:zoneinfo_data_file:s0    0
> > > 2017-04-07 18:32 asdf
> > >
> > > note how the label of the "asdf" file matches the label of the
> > > enclosing directory.
> > >
> > > However, that's not true when the directory uses categories. In
> > > that
> > > case, the newly created file inherits the label, but not the
> > > categories. For example:
> > >
> > > bullhead:/data/data # cd /data/data/com.android.chrome
> > > bullhead:/data/data/com.android.chrome # ls -ladZ .
> > > drwx------ 6 u0_a60 u0_a60 u:object_r:app_data_file:s0:c512,c768
> > > 4096
> > > 1971-07-15 15:31 .
> > > bullhead:/data/data/com.android.chrome # touch asdf
> > > bullhead:/data/data/com.android.chrome # ls -laZd . asdf
> > > drwx------ 6 u0_a60 u0_a60 u:object_r:app_data_file:s0:c512,c768
> > > 4096
> > > 2017-04-07 18:35 .
> > > -rw-rw-rw- 1
> > > root   root   u:object_r:app_data_file:s0              0
> > > 2017-04-07 18:35 asdf
> > >
> > > Note how the label is maintained, but the "c512,c768" portion is
> > > not
> > > maintained. While this example occurs when I'm running in a
> > > permissive
> > > domain, it also occurs in an enforcing domain.
> > >
> > > The inconsistency seems weird, and I'm sure there's a good reason
> > > why
> > > this occurs that I'm not familiar with. Can someone help me
> > > understand
> > > if this is expected, and if so, why?
> >
> > First, the good news is that you get to specify which behavior you
> > want
> > for each context field and object class through policy (as long as
> > your
> > kernel and policy version supports it), see:
> > https://selinuxproject.org/page/DefaultRules
> >
> > Second, there are different defaults for each of the fields of the
> > security contexts based on what is most normative for that particular
> > security model.  The user identity defaults to that of the creating
> > process since we typically do not allow a process to create files
> > with
> > a different user identity and want the file to reflect its creator
> > (this is defined through constraints on user identity in policies
> > that
> > define more than one, unlike Android). The role defaults to the fixed
> > object_r role because originally we didn't envision a use case for
> > roles on files.  The MLS range defaults to the low/current level of
> > the
> > process because a process is typically not allowed to create files at
> > a
> > different level and we want the file to reflect the sensitivity of
> > the
> > data which originated from the process. The type defaults to a
> > related
> > object type (in this case that of the parent directory) because
> > process
> > domains and object types are separate (aside from overlapping use for
> > /proc/pid) and the relationships among them are explicit through the
> > TE
> > rules / access matrix rather than through implicit rules.
> >
> > Of course, in addition to being able to globally configure the
> > default
> > behavior, you can also customize specific cases through the
> > role/type/range_transition rules.
> >
> > With your example above, you wanted the file to inherit the level of
> > the directory, but consider the situation where a process with
> > categories (:s0:c512,c768) creates a file in some shared
> > (mlstrustedobject) directory that is just :s0.  Do you want that file
> > to end up as just :s0?  In the MLS world, that would be a downgrade /
> > info leak.
>
> I guess that's not a great example since then the file would also end
> up with the same type by default and thus would be a mlstrustedobject
> and accessible regardless of its level.  So you'd want a type
> transition to a derived type for files created in that directory to
> avoid that.
>
> _______________________________________________
> Selinux mailing list
> Selinux@tycho.nsa.gov
> To unsubscribe, send email to Selinux-leave@tycho.nsa.gov.
> To get help, send an email containing "help" to
> Selinux-request@tycho.nsa.gov.

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Re: MLS directory label inheritance rules

[Joshua Brindle]

Dennis Sherrell wrote:
> In a thread ending with Nick Kravelich's contact infirmation, it was
> written:
>
> "
> If you write top secret data it should stay top secret even if you're
> writing to a folder that is normally reserved for secret data, or perhaps
> mixed data. Iirc it uses the MLS of the process when creating the file
> entry."
>
> I disagree. Top Secret data shoud not be written to a folder which was not
> provisioned for such. Allowing persons or processess of lower
> classification access to "containers" with higher clearance requirements
> could cause a data spill. Any thoughts as to active handling of such?
>

These are just the default labeling rules. The reading or writing would 
still need to be allowed by the TE policy and not removed by the 
constraints. MLS constraints should prevent a write from a TS subject to 
a S object regardless of what the default rule says the label should be.

> Dennis Sherrell
> Sherrell Consulting
> Bakersfield, California Company #136601
> Counter-Terrorism
> Cybernetic Countermeasure Developer
>
> On Fri, Apr 7, 2017, 12:55 PM Stephen Smalley<sds@tycho.nsa.gov>  wrote:
>
>> On Fri, 2017-04-07 at 15:41 -0400, Stephen Smalley wrote:
>>> On Fri, 2017-04-07 at 11:39 -0700, Nick Kralevich wrote:
>>>> When a file is created in a directory, the default label for the
>>>> file
>>>> is based on the label of the enclosing directory (unless something
>>>> like setfscreatecon is used). For example:
>>>>
>>>> bullhead:/ # cd /data/misc/zoneinfo/
>>>>
>>>> bullhead:/data/misc/zoneinfo # ls -ladZ .
>>>> drwxrwxr-x 2 system system u:object_r:zoneinfo_data_file:s0 4096
>>>> 1971-06-19 17:07 .
>>>> bullhead:/data/misc/zoneinfo # touch asdf
>>>> bullhead:/data/misc/zoneinfo # ls -ladZ . asdf
>>>>
>>>> drwxrwxr-x 2 system system u:object_r:zoneinfo_data_file:s0 4096
>>>> 2017-04-07 18:32 .
>>>> -rw-rw-rw- 1 root   root   u:object_r:zoneinfo_data_file:s0    0
>>>> 2017-04-07 18:32 asdf
>>>>
>>>> note how the label of the "asdf" file matches the label of the
>>>> enclosing directory.
>>>>
>>>> However, that's not true when the directory uses categories. In
>>>> that
>>>> case, the newly created file inherits the label, but not the
>>>> categories. For example:
>>>>
>>>> bullhead:/data/data # cd /data/data/com.android.chrome
>>>> bullhead:/data/data/com.android.chrome # ls -ladZ .
>>>> drwx------ 6 u0_a60 u0_a60 u:object_r:app_data_file:s0:c512,c768
>>>> 4096
>>>> 1971-07-15 15:31 .
>>>> bullhead:/data/data/com.android.chrome # touch asdf
>>>> bullhead:/data/data/com.android.chrome # ls -laZd . asdf
>>>> drwx------ 6 u0_a60 u0_a60 u:object_r:app_data_file:s0:c512,c768
>>>> 4096
>>>> 2017-04-07 18:35 .
>>>> -rw-rw-rw- 1
>>>> root   root   u:object_r:app_data_file:s0              0
>>>> 2017-04-07 18:35 asdf
>>>>
>>>> Note how the label is maintained, but the "c512,c768" portion is
>>>> not
>>>> maintained. While this example occurs when I'm running in a
>>>> permissive
>>>> domain, it also occurs in an enforcing domain.
>>>>
>>>> The inconsistency seems weird, and I'm sure there's a good reason
>>>> why
>>>> this occurs that I'm not familiar with. Can someone help me
>>>> understand
>>>> if this is expected, and if so, why?
>>> First, the good news is that you get to specify which behavior you
>>> want
>>> for each context field and object class through policy (as long as
>>> your
>>> kernel and policy version supports it), see:
>>> https://selinuxproject.org/page/DefaultRules
>>>
>>> Second, there are different defaults for each of the fields of the
>>> security contexts based on what is most normative for that particular
>>> security model.  The user identity defaults to that of the creating
>>> process since we typically do not allow a process to create files
>>> with
>>> a different user identity and want the file to reflect its creator
>>> (this is defined through constraints on user identity in policies
>>> that
>>> define more than one, unlike Android). The role defaults to the fixed
>>> object_r role because originally we didn't envision a use case for
>>> roles on files.  The MLS range defaults to the low/current level of
>>> the
>>> process because a process is typically not allowed to create files at
>>> a
>>> different level and we want the file to reflect the sensitivity of
>>> the
>>> data which originated from the process. The type defaults to a
>>> related
>>> object type (in this case that of the parent directory) because
>>> process
>>> domains and object types are separate (aside from overlapping use for
>>> /proc/pid) and the relationships among them are explicit through the
>>> TE
>>> rules / access matrix rather than through implicit rules.
>>>
>>> Of course, in addition to being able to globally configure the
>>> default
>>> behavior, you can also customize specific cases through the
>>> role/type/range_transition rules.
>>>
>>> With your example above, you wanted the file to inherit the level of
>>> the directory, but consider the situation where a process with
>>> categories (:s0:c512,c768) creates a file in some shared
>>> (mlstrustedobject) directory that is just :s0.  Do you want that file
>>> to end up as just :s0?  In the MLS world, that would be a downgrade /
>>> info leak.
>> I guess that's not a great example since then the file would also end
>> up with the same type by default and thus would be a mlstrustedobject
>> and accessible regardless of its level.  So you'd want a type
>> transition to a derived type for files created in that directory to
>> avoid that.
>>
>> _______________________________________________
>> Selinux mailing list
>> Selinux@tycho.nsa.gov
>> To unsubscribe, send email to Selinux-leave@tycho.nsa.gov.
>> To get help, send an email containing "help" to
>> Selinux-request@tycho.nsa.gov.
>
> _______________________________________________
> Selinux mailing list
> Selinux@tycho.nsa.gov
> To unsubscribe, send email to Selinux-leave@tycho.nsa.gov.
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Re: MLS directory label inheritance rules

[Casey Schaufler]

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On 4/7/2017 1:15 PM, Dennis Sherrell wrote:
>
> In a thread ending with Nick Kravelich's contact infirmation, it was written:
>
> "
> If you write top secret data it should stay top secret even if you're writing to a folder that is normally reserved for secret data, or perhaps mixed data. Iirc it uses the MLS of the process when creating the file entry."
>
> I disagree. Top Secret data shoud not be written to a folder which was not provisioned for such. Allowing persons or processess of lower classification access to "containers" with higher clearance requirements could cause a data spill. Any thoughts as to active handling of such?
>
If you can only put TS objects in TS directories where
do you put the first TS directory? While it is generally
true that you don't want to put TS things in places that
uncleared subjects can't see them, you have to allow for
the exception of a TS directory in a less than TS directory.
Otherwise you can only have single-level filesystems.

We ran into this question way back in the Orange Book era.
Although there were several "clever" ideas put forth, the
model of allowing higher level objects to be created in
lower level directories *under controlled circumstances*
was gradually adopted as the only viable option.

> Dennis Sherrell
> Sherrell Consulting
> Bakersfield, California Company #136601
> Counter-Terrorism
> Cybernetic Countermeasure Developer
>
>
> On Fri, Apr 7, 2017, 12:55 PM Stephen Smalley <sds@tycho.nsa.gov <mailto:sds@tycho.nsa.gov>> wrote:
>
>     On Fri, 2017-04-07 at 15:41 -0400, Stephen Smalley wrote:
>     > On Fri, 2017-04-07 at 11:39 -0700, Nick Kralevich wrote:
>     > > When a file is created in a directory, the default label for the
>     > > file
>     > > is based on the label of the enclosing directory (unless something
>     > > like setfscreatecon is used). For example:
>     > >
>     > > bullhead:/ # cd /data/misc/zoneinfo/
>     > >
>     > > bullhead:/data/misc/zoneinfo # ls -ladZ .
>     > > drwxrwxr-x 2 system system u:object_r:zoneinfo_data_file:s0 4096
>     > > 1971-06-19 17:07 .
>     > > bullhead:/data/misc/zoneinfo # touch asdf
>     > > bullhead:/data/misc/zoneinfo # ls -ladZ . asdf
>     > >
>     > > drwxrwxr-x 2 system system u:object_r:zoneinfo_data_file:s0 4096
>     > > 2017-04-07 18:32 .
>     > > -rw-rw-rw- 1 root   root   u:object_r:zoneinfo_data_file:s0    0
>     > > 2017-04-07 18:32 asdf
>     > >
>     > > note how the label of the "asdf" file matches the label of the
>     > > enclosing directory.
>     > >
>     > > However, that's not true when the directory uses categories. In
>     > > that
>     > > case, the newly created file inherits the label, but not the
>     > > categories. For example:
>     > >
>     > > bullhead:/data/data # cd /data/data/com.android.chrome
>     > > bullhead:/data/data/com.android.chrome # ls -ladZ .
>     > > drwx------ 6 u0_a60 u0_a60 u:object_r:app_data_file:s0:c512,c768
>     > > 4096
>     > > 1971-07-15 15:31 .
>     > > bullhead:/data/data/com.android.chrome # touch asdf
>     > > bullhead:/data/data/com.android.chrome # ls -laZd . asdf
>     > > drwx------ 6 u0_a60 u0_a60 u:object_r:app_data_file:s0:c512,c768
>     > > 4096
>     > > 2017-04-07 18:35 .
>     > > -rw-rw-rw- 1
>     > > root   root   u:object_r:app_data_file:s0              0
>     > > 2017-04-07 18:35 asdf
>     > >
>     > > Note how the label is maintained, but the "c512,c768" portion is
>     > > not
>     > > maintained. While this example occurs when I'm running in a
>     > > permissive
>     > > domain, it also occurs in an enforcing domain.
>     > >
>     > > The inconsistency seems weird, and I'm sure there's a good reason
>     > > why
>     > > this occurs that I'm not familiar with. Can someone help me
>     > > understand
>     > > if this is expected, and if so, why?
>     >
>     > First, the good news is that you get to specify which behavior you
>     > want
>     > for each context field and object class through policy (as long as
>     > your
>     > kernel and policy version supports it), see:
>     > https://selinuxproject.org/page/DefaultRules
>     >
>     > Second, there are different defaults for each of the fields of the
>     > security contexts based on what is most normative for that particular
>     > security model.  The user identity defaults to that of the creating
>     > process since we typically do not allow a process to create files
>     > with
>     > a different user identity and want the file to reflect its creator
>     > (this is defined through constraints on user identity in policies
>     > that
>     > define more than one, unlike Android). The role defaults to the fixed
>     > object_r role because originally we didn't envision a use case for
>     > roles on files.  The MLS range defaults to the low/current level of
>     > the
>     > process because a process is typically not allowed to create files at
>     > a
>     > different level and we want the file to reflect the sensitivity of
>     > the
>     > data which originated from the process. The type defaults to a
>     > related
>     > object type (in this case that of the parent directory) because
>     > process
>     > domains and object types are separate (aside from overlapping use for
>     > /proc/pid) and the relationships among them are explicit through the
>     > TE
>     > rules / access matrix rather than through implicit rules.
>     >
>     > Of course, in addition to being able to globally configure the
>     > default
>     > behavior, you can also customize specific cases through the
>     > role/type/range_transition rules.
>     >
>     > With your example above, you wanted the file to inherit the level of
>     > the directory, but consider the situation where a process with
>     > categories (:s0:c512,c768) creates a file in some shared
>     > (mlstrustedobject) directory that is just :s0.  Do you want that file
>     > to end up as just :s0?  In the MLS world, that would be a downgrade /
>     > info leak.
>
>     I guess that's not a great example since then the file would also end
>     up with the same type by default and thus would be a mlstrustedobject
>     and accessible regardless of its level.  So you'd want a type
>     transition to a derived type for files created in that directory to
>     avoid that.
>
>     _______________________________________________
>     Selinux mailing list
>     Selinux@tycho.nsa.gov <mailto:Selinux@tycho.nsa.gov>
>     To unsubscribe, send email to Selinux-leave@tycho.nsa.gov <mailto:Selinux-leave@tycho.nsa.gov>.
>     To get help, send an email containing "help" to Selinux-request@tycho.nsa.gov <mailto:Selinux-request@tycho.nsa.gov>.
>
>
>
> _______________________________________________
> Selinux mailing list
> Selinux@tycho.nsa.gov
> To unsubscribe, send email to Selinux-leave@tycho.nsa.gov.
> To get help, send an email containing "help" to Selinux-request@tycho.nsa.gov.


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Re: MLS directory label inheritance rules

[William Roberts]

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On Apr 7, 2017 13:16, "Dennis Sherrell" <sherrellconsulting@gmail.com>
wrote:

In a thread ending with Nick Kravelich's contact infirmation, it was
written:

"
If you write top secret data it should stay top secret even if you're
writing to a folder that is normally reserved for secret data, or perhaps
mixed data. Iirc it uses the MLS of the process when creating the file
entry."

I disagree. Top Secret data shoud not be written to a folder which was not
provisioned for such.

You guys are too nuanced at times, it was meant to be a very simple
contrived answer without typing a long diatribe. In general Stephens shared
tmp example is in essence what I was going for.



Allowing persons or processess of lower classification access to
"containers" with higher clearance requirements could cause a data spill.
Any thoughts as to active handling of such?

Dennis Sherrell
Sherrell Consulting
Bakersfield, California Company #136601
Counter-Terrorism
Cybernetic Countermeasure Developer

On Fri, Apr 7, 2017, 12:55 PM Stephen Smalley <sds@tycho.nsa.gov> wrote:

> On Fri, 2017-04-07 at 15:41 -0400, Stephen Smalley wrote:
> > On Fri, 2017-04-07 at 11:39 -0700, Nick Kralevich wrote:
> > > When a file is created in a directory, the default label for the
> > > file
> > > is based on the label of the enclosing directory (unless something
> > > like setfscreatecon is used). For example:
> > >
> > > bullhead:/ # cd /data/misc/zoneinfo/
> > >
> > > bullhead:/data/misc/zoneinfo # ls -ladZ .
> > > drwxrwxr-x 2 system system u:object_r:zoneinfo_data_file:s0 4096
> > > 1971-06-19 17:07 .
> > > bullhead:/data/misc/zoneinfo # touch asdf
> > > bullhead:/data/misc/zoneinfo # ls -ladZ . asdf
> > >
> > > drwxrwxr-x 2 system system u:object_r:zoneinfo_data_file:s0 4096
> > > 2017-04-07 18:32 .
> > > -rw-rw-rw- 1 root   root   u:object_r:zoneinfo_data_file:s0    0
> > > 2017-04-07 18:32 asdf
> > >
> > > note how the label of the "asdf" file matches the label of the
> > > enclosing directory.
> > >
> > > However, that's not true when the directory uses categories. In
> > > that
> > > case, the newly created file inherits the label, but not the
> > > categories. For example:
> > >
> > > bullhead:/data/data # cd /data/data/com.android.chrome
> > > bullhead:/data/data/com.android.chrome # ls -ladZ .
> > > drwx------ 6 u0_a60 u0_a60 u:object_r:app_data_file:s0:c512,c768
> > > 4096
> > > 1971-07-15 15:31 .
> > > bullhead:/data/data/com.android.chrome # touch asdf
> > > bullhead:/data/data/com.android.chrome # ls -laZd . asdf
> > > drwx------ 6 u0_a60 u0_a60 u:object_r:app_data_file:s0:c512,c768
> > > 4096
> > > 2017-04-07 18:35 .
> > > -rw-rw-rw- 1
> > > root   root   u:object_r:app_data_file:s0              0
> > > 2017-04-07 18:35 asdf
> > >
> > > Note how the label is maintained, but the "c512,c768" portion is
> > > not
> > > maintained. While this example occurs when I'm running in a
> > > permissive
> > > domain, it also occurs in an enforcing domain.
> > >
> > > The inconsistency seems weird, and I'm sure there's a good reason
> > > why
> > > this occurs that I'm not familiar with. Can someone help me
> > > understand
> > > if this is expected, and if so, why?
> >
> > First, the good news is that you get to specify which behavior you
> > want
> > for each context field and object class through policy (as long as
> > your
> > kernel and policy version supports it), see:
> > https://selinuxproject.org/page/DefaultRules
> >
> > Second, there are different defaults for each of the fields of the
> > security contexts based on what is most normative for that particular
> > security model.  The user identity defaults to that of the creating
> > process since we typically do not allow a process to create files
> > with
> > a different user identity and want the file to reflect its creator
> > (this is defined through constraints on user identity in policies
> > that
> > define more than one, unlike Android). The role defaults to the fixed
> > object_r role because originally we didn't envision a use case for
> > roles on files.  The MLS range defaults to the low/current level of
> > the
> > process because a process is typically not allowed to create files at
> > a
> > different level and we want the file to reflect the sensitivity of
> > the
> > data which originated from the process. The type defaults to a
> > related
> > object type (in this case that of the parent directory) because
> > process
> > domains and object types are separate (aside from overlapping use for
> > /proc/pid) and the relationships among them are explicit through the
> > TE
> > rules / access matrix rather than through implicit rules.
> >
> > Of course, in addition to being able to globally configure the
> > default
> > behavior, you can also customize specific cases through the
> > role/type/range_transition rules.
> >
> > With your example above, you wanted the file to inherit the level of
> > the directory, but consider the situation where a process with
> > categories (:s0:c512,c768) creates a file in some shared
> > (mlstrustedobject) directory that is just :s0.  Do you want that file
> > to end up as just :s0?  In the MLS world, that would be a downgrade /
> > info leak.
>
> I guess that's not a great example since then the file would also end
> up with the same type by default and thus would be a mlstrustedobject
> and accessible regardless of its level.  So you'd want a type
> transition to a derived type for files created in that directory to
> avoid that.
>
> _______________________________________________
> Selinux mailing list
> Selinux@tycho.nsa.gov
> To unsubscribe, send email to Selinux-leave@tycho.nsa.gov.
> To get help, send an email containing "help" to
> Selinux-request@tycho.nsa.gov.


_______________________________________________
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Selinux@tycho.nsa.gov
To unsubscribe, send email to Selinux-leave@tycho.nsa.gov.
To get help, send an email containing "help" to
Selinux-request@tycho.nsa.gov.

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