Re: [RFC PATCH v4 3/4] ima: define '.ima' as a builtin 'trusted' keyring

[Dmitry Kasatkin <d.kasatkin@samsung.com>]

On 09/06/14 14:06, Mimi Zohar wrote:
> On Fri, 2014-05-30 at 19:05 +0300, Dmitry Kasatkin wrote:
>> On 28 May 2014 22:26, Mimi Zohar <zohar@linux.vnet.ibm.com> wrote:
>>> On Wed, 2014-05-28 at 21:55 +0300, Dmitry Kasatkin wrote:
>>>> On 28 May 2014 18:09, Mimi Zohar <zohar@linux.vnet.ibm.com> wrote:
>>>>> Require all keys added to the IMA keyring be signed by an
>>>>> existing trusted key on the system trusted keyring.
>>>>>
>>>>> Changelog v1:
>>>>> - don't link IMA trusted keyring to user keyring
>>>>>
>>>>> Changelog:
>>>>> - define stub integrity_init_keyring() function (reported-by Fengguang Wu)
>>>>> - differentiate between regular and trusted keyring names.
>>>>> - replace printk with pr_info (D. Kasatkin)
>>>>> - only make the IMA keyring a trusted keyring (reported-by D. Kastatkin)
>>>>> - define stub integrity_init_keyring() definition based on
>>>>>   CONFIG_INTEGRITY_SIGNATURE, not CONFIG_INTEGRITY_ASYMMETRIC_KEYS.
>>>>>   (reported-by Jim Davis)
>>>>>
>>>>> Signed-off-by: Mimi Zohar<zohar@linux.vnet.ibm.com>
>>>>> ---
>>>>>  security/integrity/digsig.c           | 26 +++++++++++++++++++++++++-
>>>>>  security/integrity/ima/Kconfig        |  8 ++++++++
>>>>>  security/integrity/ima/ima_appraise.c | 11 +++++++++++
>>>>>  security/integrity/integrity.h        |  5 +++++
>>>>>  4 files changed, 49 insertions(+), 1 deletion(-)
>>>>>
>>>>> diff --git a/security/integrity/digsig.c b/security/integrity/digsig.c
>>>>> index b4af4eb..7da5f9c 100644
>>>>> --- a/security/integrity/digsig.c
>>>>> +++ b/security/integrity/digsig.c
>>>>> @@ -13,7 +13,9 @@
>>>>>  #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
>>>>>
>>>>>  #include <linux/err.h>
>>>>> +#include <linux/sched.h>
>>>>>  #include <linux/rbtree.h>
>>>>> +#include <linux/cred.h>
>>>>>  #include <linux/key-type.h>
>>>>>  #include <linux/digsig.h>
>>>>>
>>>>> @@ -24,7 +26,11 @@ static struct key *keyring[INTEGRITY_KEYRING_MAX];
>>>>>  static const char *keyring_name[INTEGRITY_KEYRING_MAX] = {
>>>>>         "_evm",
>>>>>         "_module",
>>>>> +#ifndef CONFIG_IMA_TRUSTED_KEYRING
>>>>>         "_ima",
>>>>> +#else
>>>>> +       ".ima",
>>>>> +#endif
>>>>>  };
>>>>>
>>>>>  int integrity_digsig_verify(const unsigned int id, const char *sig, int siglen,
>>>>> @@ -35,7 +41,7 @@ int integrity_digsig_verify(const unsigned int id, const char *sig, int siglen,
>>>>>
>>>>>         if (!keyring[id]) {
>>>>>                 keyring[id] =
>>>>> -                       request_key(&key_type_keyring, keyring_name[id], NULL);
>>>>> +                   request_key(&key_type_keyring, keyring_name[id], NULL);
>>>>>                 if (IS_ERR(keyring[id])) {
>>>>>                         int err = PTR_ERR(keyring[id]);
>>>>>                         pr_err("no %s keyring: %d\n", keyring_name[id], err);
>>>>> @@ -56,3 +62,21 @@ int integrity_digsig_verify(const unsigned int id, const char *sig, int siglen,
>>>>>
>>>>>         return -EOPNOTSUPP;
>>>>>  }
>>>>> +
>>>>> +int integrity_init_keyring(const unsigned int id)
>>>>> +{
>>>>> +       const struct cred *cred = current_cred();
>>>>> +
>>>>> +       keyring[id] = keyring_alloc(keyring_name[id], KUIDT_INIT(0),
>>>>> +                                   KGIDT_INIT(0), cred,
>>>>> +                                   ((KEY_POS_ALL & ~KEY_POS_SETATTR) |
>>>>> +                                     KEY_USR_VIEW | KEY_USR_READ |
>>>>> +                                     KEY_USR_WRITE | KEY_USR_SEARCH),
>>>>> +                                   KEY_ALLOC_NOT_IN_QUOTA, NULL);
>>>> Last parameter "destination" is NULL. It makes keyring "unsearchable"
>>>> from user space.
>>>> It prevents loading trusted keys from user-space, e.g. initramfs...
>>>>
>>>> Should it be "cred->user->uid_keyring"??
>>> David extended keyctl with the '%keyring' option.  For example,
>>> "keyctl show %keyring:.ima" returns the .ima keyring id with a list of
>>> all the keys.
>>>
>> That is not kernel feature, but keyctl feature as I can see.
>> It will not find keyring from user space..
>>
>> keyutils.c 3.5.7 has this kind of thing
>> f = fopen("/proc/keys", "r");
>>
>> But it would require CONFIG_PROC_KEYS to be enabled.
>>
>> May be David may comment...
> David commented on an prior patch set, which defined a new id for the
> system trusted keyring. For hjs comments, refer to
> http://marc.info/?l=linux-security-module&m=137829415530503&w=2
>
> thanks,
>
> Mimi

Fine for me if such API is fine for David.

I just checked one again. They option to enable /proc/keys is called
CONFIG_KEYS_DEBUG_PROC_KEYS

It is a bit weired that in order to be able to load keys to trusted
keyring it is necessary to enable *_DEBUG_* option.

David stated: (1) Make /proc/keys always present if CONFIG_KEYS=y.

It is not there yet...

Should than CONFIG_IMA_TRUSTED_KEYRING "select
CONFIG_KEYS_DEBUG_PROC_KEYS" by David suggestion?

- Dmitry

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