[v5,14/16] ima: Use mac_admin_ns_capable() to check corresponding capability

Commit Message

Stefan Berger Dec. 8, 2021, 10:18 p.m. UTC

Use mac_admin_ns_capable() to check corresponding capability to allow
read/write IMA policy without CAP_SYS_ADMIN but with CAP_MAC_ADMIN.

Signed-off-by: Denis Semakin <[e-mail]>
Signed-off-by: Stefan Berger <[e-mail]>
---
 include/linux/capability.h      | 6 ++++++
 security/integrity/ima/ima_fs.c | 2 +-
 2 files changed, 7 insertions(+), 1 deletion(-)

Comments

Denis Semakin Dec. 9, 2021, 7:22 a.m. UTC | #1

Hi. 
My question won't be about capabilities. I'm wondering how IMA-ns which is associated with USER-ns and is created during USER-ns creation
would be used by some namespaces orchestration systems, e.g. Kubernetes?.. It seems that it can be run without any user namespaces... 
Their community just discuss this opportunity to support User namespaces. (see https://github.com/kubernetes/enhancements/pull/2101)
Looks like currently IMA-ns will not be applicable for Kubernetes.

Br,
Denis

-----Original Message-----
From: Stefan Berger [mailto:[e-mail]] 
Sent: Thursday, December 9, 2021 1:18 AM
To: [e-mail]
Cc: [e-mail]; [e-mail]; [e-mail]; [e-mail]; [e-mail]; [e-mail]; Krzysztof Struczynski <[e-mail]>; Roberto Sassu <[e-mail]>; [e-mail]; [e-mail]; [e-mail]; [e-mail]; [e-mail]; [e-mail]; [e-mail]; [e-mail]; [e-mail]; [e-mail]; [e-mail]; Stefan Berger <[e-mail]>; Denis Semakin <[e-mail]>
Subject: [PATCH v5 14/16] ima: Use mac_admin_ns_capable() to check corresponding capability

Use mac_admin_ns_capable() to check corresponding capability to allow read/write IMA policy without CAP_SYS_ADMIN but with CAP_MAC_ADMIN.

Signed-off-by: Denis Semakin <[e-mail]>
Signed-off-by: Stefan Berger <[e-mail]>
---
 include/linux/capability.h      | 6 ++++++
 security/integrity/ima/ima_fs.c | 2 +-
 2 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/include/linux/capability.h b/include/linux/capability.h index 65efb74c3585..991579178f32 100644
--- a/include/linux/capability.h
+++ b/include/linux/capability.h
@@ -270,6 +270,12 @@ static inline bool checkpoint_restore_ns_capable(struct user_namespace *ns)
 		ns_capable(ns, CAP_SYS_ADMIN);
 }
 
+static inline bool mac_admin_ns_capable(struct user_namespace *ns) {
+	return ns_capable(ns, CAP_MAC_ADMIN) ||
+		ns_capable(ns, CAP_SYS_ADMIN);
+}
+
 /* audit system wants to get cap info from files as well */  int get_vfs_caps_from_disk(struct user_namespace *mnt_userns,
 			   const struct dentry *dentry,
diff --git a/security/integrity/ima/ima_fs.c b/security/integrity/ima/ima_fs.c index 0e582ceecc7f..a749a3e79304 100644
--- a/security/integrity/ima/ima_fs.c
+++ b/security/integrity/ima/ima_fs.c
@@ -394,7 +394,7 @@ static int ima_open_policy(struct inode *inode, struct file *filp)  #else
 		if ((filp->f_flags & O_ACCMODE) != O_RDONLY)
 			return -EACCES;
-		if (!capable(CAP_SYS_ADMIN))
+		if (!mac_admin_ns_capable(ns->user_ns))
 			return -EPERM;
 		return seq_open(filp, &ima_policy_seqops);  #endif
--
2.31.1

Denis Semakin Dec. 9, 2021, 8:09 a.m. UTC | #2

Following that thoughts...
Will it be so incorrectly to unbound IMA-ns from USER-ns?
I realize that it could lead a lot of problems but it is still unclear will current IMA-ns will be useful for Kuber...
How userland supposed to use current IMA-ns implementation?

Br,
Denis

-----Original Message-----
From: Denis Semakin 
Sent: Thursday, December 9, 2021 10:22 AM
To: 'Stefan Berger' <[e-mail]>; [e-mail]
Cc: [e-mail]; [e-mail]; [e-mail]; [e-mail]; [e-mail]; [e-mail]; Krzysztof Struczynski <[e-mail]>; Roberto Sassu <[e-mail]>; [e-mail]; [e-mail]; [e-mail]; [e-mail]; [e-mail]; [e-mail]; [e-mail]; [e-mail]; [e-mail]; [e-mail]; [e-mail]
Subject: RE: [PATCH v5 14/16] ima: Use mac_admin_ns_capable() to check corresponding capability

Hi. 
My question won't be about capabilities. I'm wondering how IMA-ns which is associated with USER-ns and is created during USER-ns creation would be used by some namespaces orchestration systems, e.g. Kubernetes?.. It seems that it can be run without any user namespaces... 
Their community just discuss this opportunity to support User namespaces. (see https://github.com/kubernetes/enhancements/pull/2101)
Looks like currently IMA-ns will not be applicable for Kubernetes.

Br,
Denis

-----Original Message-----
From: Stefan Berger [mailto:[e-mail]]
Sent: Thursday, December 9, 2021 1:18 AM
To: [e-mail]
Cc: [e-mail]; [e-mail]; [e-mail]; [e-mail]; [e-mail]; [e-mail]; Krzysztof Struczynski <[e-mail]>; Roberto Sassu <[e-mail]>; [e-mail]; [e-mail]; [e-mail]; [e-mail]; [e-mail]; [e-mail]; [e-mail]; [e-mail]; [e-mail]; [e-mail]; [e-mail]; Stefan Berger <[e-mail]>; Denis Semakin <[e-mail]>
Subject: [PATCH v5 14/16] ima: Use mac_admin_ns_capable() to check corresponding capability

Use mac_admin_ns_capable() to check corresponding capability to allow read/write IMA policy without CAP_SYS_ADMIN but with CAP_MAC_ADMIN.

Signed-off-by: Denis Semakin <[e-mail]>
Signed-off-by: Stefan Berger <[e-mail]>
---
 include/linux/capability.h      | 6 ++++++
 security/integrity/ima/ima_fs.c | 2 +-
 2 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/include/linux/capability.h b/include/linux/capability.h index 65efb74c3585..991579178f32 100644
--- a/include/linux/capability.h
+++ b/include/linux/capability.h
@@ -270,6 +270,12 @@ static inline bool checkpoint_restore_ns_capable(struct user_namespace *ns)
 		ns_capable(ns, CAP_SYS_ADMIN);
 }
 
+static inline bool mac_admin_ns_capable(struct user_namespace *ns) {
+	return ns_capable(ns, CAP_MAC_ADMIN) ||
+		ns_capable(ns, CAP_SYS_ADMIN);
+}
+
 /* audit system wants to get cap info from files as well */  int get_vfs_caps_from_disk(struct user_namespace *mnt_userns,
 			   const struct dentry *dentry,
diff --git a/security/integrity/ima/ima_fs.c b/security/integrity/ima/ima_fs.c index 0e582ceecc7f..a749a3e79304 100644
--- a/security/integrity/ima/ima_fs.c
+++ b/security/integrity/ima/ima_fs.c
@@ -394,7 +394,7 @@ static int ima_open_policy(struct inode *inode, struct file *filp)  #else
 		if ((filp->f_flags & O_ACCMODE) != O_RDONLY)
 			return -EACCES;
-		if (!capable(CAP_SYS_ADMIN))
+		if (!mac_admin_ns_capable(ns->user_ns))
 			return -EPERM;
 		return seq_open(filp, &ima_policy_seqops);  #endif
--
2.31.1

James Bottomley Dec. 9, 2021, 1:23 p.m. UTC | #3

On Thu, 2021-12-09 at 07:22 +0000, Denis Semakin wrote:
> Hi. 
> My question won't be about capabilities. I'm wondering how IMA-ns
> which is associated with USER-ns and is created during USER-ns
> creation would be used by some namespaces orchestration systems, e.g.
> Kubernetes?

Orchestration systems that don't adopt the user namespace can't really
run containers requiring admin correctly without giving them root minus
some capabilities, which is rather unsafe, so the expectation is that
they'll all figure it out eventually for security reasons.

> .. It seems that it can be run without any user namespaces... 
> Their community just discuss this opportunity to support User
> namespaces. (see https://github.com/kubernetes/enhancements/pull/2101
> ) Looks like currently IMA-ns will not be applicable for Kubernetes.

Well, lets just say it adds one more reason to get kubernetes to
finally run rootless privileged containers correctly ...

James

Serge E. Hallyn Dec. 11, 2021, 3:02 p.m. UTC | #4

IMO yes it is unsafe, however I concede that I am not sufficiently familiar
with the policy language.  At least Stefan and Mimi (IIUC) want the host
policy language to be able to specify cases where an IMA ns can be
configured.  What's not clear to me is what sorts of triggers the host
IMA policy could specify that would safely identify a IMA ns generation
trigger.

Stefan, would you mind showing what such a policy statement would look like?
Does it amount to "/usr/bin/runc may create an IMA ns which escapes current
policy" ?  Or is it by UID, or any file which has a certain xattr on it?

-serge

On Thu, Dec 09, 2021 at 08:09:20AM +0000, Denis Semakin wrote:
> Following that thoughts...
> Will it be so incorrectly to unbound IMA-ns from USER-ns?
> I realize that it could lead a lot of problems but it is still unclear will current IMA-ns will be useful for Kuber...
> How userland supposed to use current IMA-ns implementation?
> 
> Br,
> Denis
> 
> -----Original Message-----
> From: Denis Semakin 
> Sent: Thursday, December 9, 2021 10:22 AM
> To: 'Stefan Berger' <[e-mail]>; [e-mail]
> Cc: [e-mail]; [e-mail]; [e-mail]; [e-mail]; [e-mail]; [e-mail]; Krzysztof Struczynski <[e-mail]>; Roberto Sassu <[e-mail]>; [e-mail]; [e-mail]; [e-mail]; [e-mail]; [e-mail]; [e-mail]; [e-mail]; [e-mail]; [e-mail]; [e-mail]; [e-mail]
> Subject: RE: [PATCH v5 14/16] ima: Use mac_admin_ns_capable() to check corresponding capability
> 
> Hi. 
> My question won't be about capabilities. I'm wondering how IMA-ns which is associated with USER-ns and is created during USER-ns creation would be used by some namespaces orchestration systems, e.g. Kubernetes?.. It seems that it can be run without any user namespaces... 
> Their community just discuss this opportunity to support User namespaces. (see https://github.com/kubernetes/enhancements/pull/2101)
> Looks like currently IMA-ns will not be applicable for Kubernetes.
> 
> Br,
> Denis
> 
> -----Original Message-----
> From: Stefan Berger [mailto:[e-mail]]
> Sent: Thursday, December 9, 2021 1:18 AM
> To: [e-mail]
> Cc: [e-mail]; [e-mail]; [e-mail]; [e-mail]; [e-mail]; [e-mail]; Krzysztof Struczynski <[e-mail]>; Roberto Sassu <[e-mail]>; [e-mail]; [e-mail]; [e-mail]; [e-mail]; [e-mail]; [e-mail]; [e-mail]; [e-mail]; [e-mail]; [e-mail]; [e-mail]; Stefan Berger <[e-mail]>; Denis Semakin <[e-mail]>
> Subject: [PATCH v5 14/16] ima: Use mac_admin_ns_capable() to check corresponding capability
> 
> Use mac_admin_ns_capable() to check corresponding capability to allow read/write IMA policy without CAP_SYS_ADMIN but with CAP_MAC_ADMIN.
> 
> Signed-off-by: Denis Semakin <[e-mail]>
> Signed-off-by: Stefan Berger <[e-mail]>
> ---
>  include/linux/capability.h      | 6 ++++++
>  security/integrity/ima/ima_fs.c | 2 +-
>  2 files changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/include/linux/capability.h b/include/linux/capability.h index 65efb74c3585..991579178f32 100644
> --- a/include/linux/capability.h
> +++ b/include/linux/capability.h
> @@ -270,6 +270,12 @@ static inline bool checkpoint_restore_ns_capable(struct user_namespace *ns)
>  		ns_capable(ns, CAP_SYS_ADMIN);
>  }
>  
> +static inline bool mac_admin_ns_capable(struct user_namespace *ns) {
> +	return ns_capable(ns, CAP_MAC_ADMIN) ||
> +		ns_capable(ns, CAP_SYS_ADMIN);
> +}
> +
>  /* audit system wants to get cap info from files as well */  int get_vfs_caps_from_disk(struct user_namespace *mnt_userns,
>  			   const struct dentry *dentry,
> diff --git a/security/integrity/ima/ima_fs.c b/security/integrity/ima/ima_fs.c index 0e582ceecc7f..a749a3e79304 100644
> --- a/security/integrity/ima/ima_fs.c
> +++ b/security/integrity/ima/ima_fs.c
> @@ -394,7 +394,7 @@ static int ima_open_policy(struct inode *inode, struct file *filp)  #else
>  		if ((filp->f_flags & O_ACCMODE) != O_RDONLY)
>  			return -EACCES;
> -		if (!capable(CAP_SYS_ADMIN))
> +		if (!mac_admin_ns_capable(ns->user_ns))
>  			return -EPERM;
>  		return seq_open(filp, &ima_policy_seqops);  #endif
> --
> 2.31.1

Stefan Berger Dec. 11, 2021, 3:38 p.m. UTC | #5

On 12/11/21 10:02, Serge E. Hallyn wrote:
> IMO yes it is unsafe, however I concede that I am not sufficiently familiar
> with the policy language.  At least Stefan and Mimi (IIUC) want the host
> policy language to be able to specify cases where an IMA ns can be
> configured.  What's not clear to me is what sorts of triggers the host
> IMA policy could specify that would safely identify a IMA ns generation
> trigger.
>
> Stefan, would you mind showing what such a policy statement would look like?
> Does it amount to "/usr/bin/runc may create an IMA ns which escapes current
> policy" ?  Or is it by UID, or any file which has a certain xattr on it?

If this policy here is active on the host then file executions 
(BPRM_CHECK) of uid=0 should be measured and audited on the host in any 
IMA namespace that uid=0 may create. We achieve this with hierarchical 
processing (v6: 10/17).

measure func=BPRM_CHECK mask=MAY_EXEC uid=0

audit func=BPRM_CHECK mask=MAY_EXEC uid=0

    Stefan


>
> -serge
>
> On Thu, Dec 09, 2021 at 08:09:20AM +0000, Denis Semakin wrote:
>> Following that thoughts...
>> Will it be so incorrectly to unbound IMA-ns from USER-ns?
>> I realize that it could lead a lot of problems but it is still unclear will current IMA-ns will be useful for Kuber...
>> How userland supposed to use current IMA-ns implementation?
>>
>> Br,
>> Denis
>>
>> -----Original Message-----
>> From: Denis Semakin
>> Sent: Thursday, December 9, 2021 10:22 AM
>> To: 'Stefan Berger' <[e-mail]>; [e-mail]
>> Cc: [e-mail]; [e-mail]; [e-mail]; [e-mail]; [e-mail]; [e-mail]; Krzysztof Struczynski <[e-mail]>; Roberto Sassu <[e-mail]>; [e-mail]; [e-mail]; [e-mail]; [e-mail]; [e-mail]; [e-mail]; [e-mail]; [e-mail]; [e-mail]; [e-mail]; [e-mail]
>> Subject: RE: [PATCH v5 14/16] ima: Use mac_admin_ns_capable() to check corresponding capability
>>
>> Hi.
>> My question won't be about capabilities. I'm wondering how IMA-ns which is associated with USER-ns and is created during USER-ns creation would be used by some namespaces orchestration systems, e.g. Kubernetes?.. It seems that it can be run without any user namespaces...
>> Their community just discuss this opportunity to support User namespaces. (see https://github.com/kubernetes/enhancements/pull/2101)
>> Looks like currently IMA-ns will not be applicable for Kubernetes.
>>
>> Br,
>> Denis
>>
>> -----Original Message-----
>> From: Stefan Berger [mailto:[e-mail]]
>> Sent: Thursday, December 9, 2021 1:18 AM
>> To: [e-mail]
>> Cc: [e-mail]; [e-mail]; [e-mail]; [e-mail]; [e-mail]; [e-mail]; Krzysztof Struczynski <[e-mail]>; Roberto Sassu <[e-mail]>; [e-mail]; [e-mail]; [e-mail]; [e-mail]; [e-mail]; [e-mail]; [e-mail]; [e-mail]; [e-mail]; [e-mail]; [e-mail]; Stefan Berger <[e-mail]>; Denis Semakin <[e-mail]>
>> Subject: [PATCH v5 14/16] ima: Use mac_admin_ns_capable() to check corresponding capability
>>
>> Use mac_admin_ns_capable() to check corresponding capability to allow read/write IMA policy without CAP_SYS_ADMIN but with CAP_MAC_ADMIN.
>>
>> Signed-off-by: Denis Semakin <[e-mail]>
>> Signed-off-by: Stefan Berger <[e-mail]>
>> ---
>>   include/linux/capability.h      | 6 ++++++
>>   security/integrity/ima/ima_fs.c | 2 +-
>>   2 files changed, 7 insertions(+), 1 deletion(-)
>>
>> diff --git a/include/linux/capability.h b/include/linux/capability.h index 65efb74c3585..991579178f32 100644
>> --- a/include/linux/capability.h
>> +++ b/include/linux/capability.h
>> @@ -270,6 +270,12 @@ static inline bool checkpoint_restore_ns_capable(struct user_namespace *ns)
>>   		ns_capable(ns, CAP_SYS_ADMIN);
>>   }
>>   
>> +static inline bool mac_admin_ns_capable(struct user_namespace *ns) {
>> +	return ns_capable(ns, CAP_MAC_ADMIN) ||
>> +		ns_capable(ns, CAP_SYS_ADMIN);
>> +}
>> +
>>   /* audit system wants to get cap info from files as well */  int get_vfs_caps_from_disk(struct user_namespace *mnt_userns,
>>   			   const struct dentry *dentry,
>> diff --git a/security/integrity/ima/ima_fs.c b/security/integrity/ima/ima_fs.c index 0e582ceecc7f..a749a3e79304 100644
>> --- a/security/integrity/ima/ima_fs.c
>> +++ b/security/integrity/ima/ima_fs.c
>> @@ -394,7 +394,7 @@ static int ima_open_policy(struct inode *inode, struct file *filp)  #else
>>   		if ((filp->f_flags & O_ACCMODE) != O_RDONLY)
>>   			return -EACCES;
>> -		if (!capable(CAP_SYS_ADMIN))
>> +		if (!mac_admin_ns_capable(ns->user_ns))
>>   			return -EPERM;
>>   		return seq_open(filp, &ima_policy_seqops);  #endif
>> --
>> 2.31.1

James Bottomley Dec. 11, 2021, 4 p.m. UTC | #6

On Sat, 2021-12-11 at 10:38 -0500, Stefan Berger wrote:
> On 12/11/21 10:02, Serge E. Hallyn wrote:
> > IMO yes it is unsafe, however I concede that I am not sufficiently
> > familiar with the policy language.  At least Stefan and Mimi (IIUC)
> > want the host policy language to be able to specify cases where an
> > IMA ns can be configured.  What's not clear to me is what sorts of
> > triggers the host IMA policy could specify that would safely
> > identify a IMA ns generation
> > trigger.
> > 
> > Stefan, would you mind showing what such a policy statement would
> > look like? Does it amount to "/usr/bin/runc may create an IMA ns
> > which escapes current policy" ?  Or is it by UID, or any file which
> > has a certain xattr on it?
> 
> If this policy here is active on the host then file executions 
> (BPRM_CHECK) of uid=0 should be measured and audited on the host in
> any IMA namespace that uid=0 may create. We achieve this with
> hierarchical processing (v6: 10/17).
> 
> measure func=BPRM_CHECK mask=MAY_EXEC uid=0
> 
> audit func=BPRM_CHECK mask=MAY_EXEC uid=0

Or perhaps to put another way that might be more useful to unprivileged
containers: if you strip the uid=0 from both of those statements, you
get a rule that logs and audits any execution.  Once you enter the IMA
namespace, in that namespace you see nothing, but outside the parent is
still logging and auditing all executions, including those inside the
container, according to its measure/audit all executions rule.  The
container can't turn that off by writes to its policy file.

So the container can never escape any policy rule imposed by the parent

James

Patch

diff --git a/include/linux/capability.h b/include/linux/capability.h
index 65efb74c3585..991579178f32 100644
--- a/include/linux/capability.h
+++ b/include/linux/capability.h
@@ -270,6 +270,12 @@  static inline bool checkpoint_restore_ns_capable(struct user_namespace *ns)
 		ns_capable(ns, CAP_SYS_ADMIN);
 }
 
+static inline bool mac_admin_ns_capable(struct user_namespace *ns)
+{
+	return ns_capable(ns, CAP_MAC_ADMIN) ||
+		ns_capable(ns, CAP_SYS_ADMIN);
+}
+
 /* audit system wants to get cap info from files as well */
 int get_vfs_caps_from_disk(struct user_namespace *mnt_userns,
 			   const struct dentry *dentry,
diff --git a/security/integrity/ima/ima_fs.c b/security/integrity/ima/ima_fs.c
index 0e582ceecc7f..a749a3e79304 100644
--- a/security/integrity/ima/ima_fs.c
+++ b/security/integrity/ima/ima_fs.c
@@ -394,7 +394,7 @@  static int ima_open_policy(struct inode *inode, struct file *filp)
 #else
 		if ((filp->f_flags & O_ACCMODE) != O_RDONLY)
 			return -EACCES;
-		if (!capable(CAP_SYS_ADMIN))
+		if (!mac_admin_ns_capable(ns->user_ns))
 			return -EPERM;
 		return seq_open(filp, &ima_policy_seqops);
 #endif