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

[Dmitry Kasatkin]

On 28 May 2014 22:26, Mimi Zohar <zohar@xxxxxxxxxxxxxxxxxx> wrote:
> On Wed, 2014-05-28 at 21:55 +0300, Dmitry Kasatkin wrote:
>> On 28 May 2014 18:09, Mimi Zohar <zohar@xxxxxxxxxxxxxxxxxx> 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@xxxxxxxxxxxxxxxxxx>
>> > ---
>> >  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...

- Dmitry


>>
>>
>> > +       if (!IS_ERR(keyring[id]))
>> > +               set_bit(KEY_FLAG_TRUSTED_ONLY, &keyring[id]->flags);
>> > +       else
>> > +               pr_info("Can't allocate %s keyring (%ld)\n",
>> > +                       keyring_name[id], PTR_ERR(keyring[id]));
>>
>> keyring[id] should be set "back" to NULL. Otherwise bad value might be
>> used in other places.
>
> Good catch, thanks.
>
>>
>> > +       return 0;
>> > +}
>> > diff --git a/security/integrity/ima/Kconfig b/security/integrity/ima/Kconfig
>> > index 81a2797..dad8d4c 100644
>> > --- a/security/integrity/ima/Kconfig
>> > +++ b/security/integrity/ima/Kconfig
>> > @@ -123,3 +123,11 @@ config IMA_APPRAISE
>> >           For more information on integrity appraisal refer to:
>> >           <http://linux-ima.sourceforge.net>
>> >           If unsure, say N.
>> > +
>> > +config IMA_TRUSTED_KEYRING
>> > +       bool "Require all keys on the _ima keyring be signed"
>> > +       depends on IMA_APPRAISE && SYSTEM_TRUSTED_KEYRING
>> > +       default y
>> > +       help
>> > +          This option requires that all keys added to the _ima
>> > +          keyring be signed by a key on the system trusted keyring.
>> > diff --git a/security/integrity/ima/ima_appraise.c b/security/integrity/ima/ima_appraise.c
>> > index d3113d4..003ff46 100644
>> > --- a/security/integrity/ima/ima_appraise.c
>> > +++ b/security/integrity/ima/ima_appraise.c
>> > @@ -385,3 +385,14 @@ int ima_inode_removexattr(struct dentry *dentry, const char *xattr_name)
>> >         }
>> >         return result;
>> >  }
>> > +
>> > +#ifdef CONFIG_IMA_TRUSTED_KEYRING
>> > +static int __init init_ima_keyring(void)
>> > +{
>> > +       int ret;
>> > +
>> > +       ret = integrity_init_keyring(INTEGRITY_KEYRING_IMA);
>> > +       return 0;
>> > +}
>> > +late_initcall(init_ima_keyring);
>>
>>
>> late_initcall(init_ima_keyring) ordering competes with late_initcall(init_ima);
>> but we want keyring to be initialized before IMA might use it.
>
>> In the case when we would load keys from ima kernel initialization
>> code, order is important.
>>
>> we already have init_ima() and ima_init calls().
>> Why not call integrity_init_keyring() from there?
>>
>> Indeed, we have one late_initcall(init_evm) for EVM, and one
>> late_initcall(init_ima) for IMA.
>>
>> It's enough...
>
> Right, there's no reason to have an additional call.
>
> thanks,
>
> Mimi
>



-- 
Thanks,
Dmitry
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/