Re: [RFC PATCH v4 4/4] KEYS: define an owner trusted keyring

[Dmitry Kasatkin]

On 28 May 2014 18:09, Mimi Zohar <zohar@xxxxxxxxxxxxxxxxxx> wrote:
> (UEFI) secure boot provides a signature chain of trust rooted in
> hardware. The signature chain of trust includes the Machine Owner
> Keys(MOKs), which cannot be modified without physical presence.
>
> Instead of allowing public keys, with certificates signed by any
> key on the system trusted keyring, to be added to a trusted
> keyring, this patch further restricts the certificates to those
> signed by the machine owner's key or chosen key.
>
> This patch defines an owner trusted keyring, defines a new boot
> command line option 'keyring=' to designate the machine owner's
> chosen key, and renames the function get_system_trusted_keyring()
> to get_system_or_owner_trusted_keyring().
>
> This patch permits the machine owner to safely identify their own
> or chosen key, without requiring it to be builtin the kernel.
>
> Signed-off-by: Mimi Zohar<zohar@xxxxxxxxxxxxxxxxxx>
> ---
>  crypto/asymmetric_keys/x509_public_key.c |  3 +-
>  include/keys/system_keyring.h            | 15 ++++--
>  include/linux/key.h                      |  4 ++
>  kernel/system_keyring.c                  | 85 ++++++++++++++++++++++++++++++++
>  security/keys/key.c                      | 20 ++++++++
>  5 files changed, 121 insertions(+), 6 deletions(-)
>
> diff --git a/crypto/asymmetric_keys/x509_public_key.c b/crypto/asymmetric_keys/x509_public_key.c
> index 1af8a30..6d52790 100644
> --- a/crypto/asymmetric_keys/x509_public_key.c
> +++ b/crypto/asymmetric_keys/x509_public_key.c
> @@ -237,7 +237,8 @@ static int x509_key_preparse(struct key_preparsed_payload *prep)
>                 if (ret < 0)
>                         goto error_free_cert;
>         } else {
> -               ret = x509_validate_trust(cert, get_system_trusted_keyring());
> +               ret = x509_validate_trust(cert,
> +                                         get_system_or_owner_trusted_keyring());
>                 if (!ret)
>                         prep->trusted = 1;
>         }
> diff --git a/include/keys/system_keyring.h b/include/keys/system_keyring.h
> index 72665eb..f665c33 100644
> --- a/include/keys/system_keyring.h
> +++ b/include/keys/system_keyring.h
> @@ -17,15 +17,20 @@
>  #include <linux/key.h>
>
>  extern struct key *system_trusted_keyring;
> -static inline struct key *get_system_trusted_keyring(void)
> -{
> -       return system_trusted_keyring;
> -}
> +extern struct key *owner_trusted_keyring;
> +
> +extern struct key *get_system_or_owner_trusted_keyring(void);
> +extern void load_owner_identified_uefi_key(key_ref_t key);
> +
>  #else
> -static inline struct key *get_system_trusted_keyring(void)
> +static inline struct key *get_system_or_owner_trusted_keyring(void)
>  {
>         return NULL;
>  }
> +
> +static void load_owner_identified_uefi_key(key_ref_t key)
> +{
> +}
>  #endif
>
>  #endif /* _KEYS_SYSTEM_KEYRING_H */
> diff --git a/include/linux/key.h b/include/linux/key.h
> index cd0abb8..861843a 100644
> --- a/include/linux/key.h
> +++ b/include/linux/key.h
> @@ -267,6 +267,10 @@ extern int wait_for_key_construction(struct key *key, bool intr);
>
>  extern int key_validate(const struct key *key);
>
> +extern int key_match(key_ref_t key,
> +                    const char *type,
> +                    const char *description);
> +
>  extern key_ref_t key_create_or_update(key_ref_t keyring,
>                                       const char *type,
>                                       const char *description,
> diff --git a/kernel/system_keyring.c b/kernel/system_keyring.c
> index 52ebc70..e9b14ac 100644
> --- a/kernel/system_keyring.c
> +++ b/kernel/system_keyring.c
> @@ -19,11 +19,75 @@
>  #include "module-internal.h"
>
>  struct key *system_trusted_keyring;
> +struct key *owner_trusted_keyring;
>  EXPORT_SYMBOL_GPL(system_trusted_keyring);
>
>  extern __initconst const u8 system_certificate_list[];
>  extern __initconst const unsigned long system_certificate_list_size;
>
> +static int use_owner_trusted_keyring;
> +
> +static char *owner_keyid;
> +static int builtin_keyring;
> +static int __init default_keyring_set(char *str)
> +{
> +       if (!str)       /* default: builtin */
> +               return 1;
> +
> +       if (strcmp(str, "system") == 0)  /* use system keyring */
> +               ;
> +       else if (strcmp(str, "builtin") == 0)  /* only builtin keys */
> +               builtin_keyring = 1;
> +       else
> +               owner_keyid = str;   /* owner local key 'id:xxxxxx' */
> +       return 1;
> +}
> +__setup("keyring=", default_keyring_set);
> +
> +/*
> + * Load the owner identified key on the 'owner' trusted keyring.
> + */
> +void load_owner_identified_uefi_key(key_ref_t key)
> +{
> +       if (!owner_keyid || use_owner_trusted_keyring)
> +               return;
> +
> +       if (!key_match(key, "asymmetric", owner_keyid))
> +               return;
> +
> +       if (key_link(owner_trusted_keyring, key_ref_to_ptr(key)) == 0) {
> +               set_bit(KEY_FLAG_TRUSTED_ONLY, &owner_trusted_keyring->flags);
> +               use_owner_trusted_keyring = 1;

This is a bit strange...
Linking any key forces to use owner trusted keyring...

> +               pr_notice("Loaded X.509 cert '%s' on .owner_keyring\n",
> +                                 key_ref_to_ptr(key)->description);
> +       }
> +}
> +
> +static void load_owner_identified_builtin_key(key_ref_t key)
> +{
> +       if (!owner_keyid && !builtin_keyring)
> +               return;
> +

It looks like builtin_keyring is useless...
Is it like linking all .system keys to owners keyring???

Why not just to return .system keyring in get_system_or_owner_trusted_keyring()
based on owner_keyid?



> +       if (!builtin_keyring && !key_match(key, "asymmetric", owner_keyid))
> +               return;
> +
> +       if (key_link(owner_trusted_keyring, key_ref_to_ptr(key)) == 0) {
> +               set_bit(KEY_FLAG_TRUSTED_ONLY, &owner_trusted_keyring->flags);
> +               use_owner_trusted_keyring = 1;

The same...
Linking any key forces to use owner trusted keyring...


> +               pr_notice("Loaded X.509 cert '%s' on .owner_keyring\n",
> +                                 key_ref_to_ptr(key)->description);
> +       }
> +}
> +
> +/*
> + * Use the owner_trusted_keyring if available
> + */
> +struct key *get_system_or_owner_trusted_keyring(void)
> +{
> +       return use_owner_trusted_keyring ? owner_trusted_keyring :
> +               system_trusted_keyring;
> +}
> +
>  /*
>   * Load the compiled-in keys
>   */
> @@ -50,6 +114,25 @@ static __init int system_trusted_keyring_init(void)
>  device_initcall(system_trusted_keyring_init);
>
>  /*
> + * Load the owner trusted key
> + */
> +static __init int owner_trusted_keyring_init(void)
> +{
> +       pr_notice("Initialize the owner trusted keyring\n");
> +
> +       owner_trusted_keyring =
> +               keyring_alloc(".owner_keyring",
> +                             KUIDT_INIT(0), KGIDT_INIT(0), current_cred(),
> +                             ((KEY_POS_ALL & ~KEY_POS_SETATTR) |
> +                             KEY_USR_VIEW | KEY_USR_READ | KEY_USR_SEARCH),
> +                             KEY_ALLOC_NOT_IN_QUOTA, NULL);
> +       if (IS_ERR(owner_trusted_keyring))
> +               panic("Can't allocate owner trusted keyring\n");
> +       return 0;
> +}
> +device_initcall(owner_trusted_keyring_init);
> +
> +/*
>   * Load the compiled-in list of X.509 certificates.
>   */
>  static __init int load_system_certificate_list(void)
> @@ -91,6 +174,8 @@ static __init int load_system_certificate_list(void)
>                 } else {
>                         pr_notice("Loaded X.509 cert '%s'\n",
>                                   key_ref_to_ptr(key)->description);
> +
> +                       load_owner_identified_builtin_key(key);
>                         key_ref_put(key);
>                 }
>                 p += plen;
> diff --git a/security/keys/key.c b/security/keys/key.c
> index 2048a11..b448ab1 100644
> --- a/security/keys/key.c
> +++ b/security/keys/key.c
> @@ -701,6 +701,26 @@ void key_type_put(struct key_type *ktype)
>         up_read(&key_types_sem);
>  }
>
> +/*
> + * Use the key type's match function to compare the key's id.
> + */
> +int key_match(key_ref_t key, const char *type, const char *description)
> +{
> +       struct keyring_index_key index_key;
> +       int ret = 0;
> +
> +       index_key.type = key_type_lookup(type);
> +       if (IS_ERR(index_key.type))
> +               goto out;
> +
> +       if (index_key.type->match &&
> +           index_key.type->match(key_ref_to_ptr(key), description))
> +               ret = 1;
> +       key_type_put(index_key.type);
> +out:
> +       return ret;
> +}
> +
>  /*
>   * Attempt to update an existing key.
>   *
> --
> 1.8.1.4
>
> --
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-- 
Thanks,
Dmitry
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