Re: [RFC PATCH 00/20] KEYS: Restrict additions to 'trusted' keyrings [ver #2]

[Petko Manolov]

I assume this is intended for 4.6 or later, correct?


		Petko


On 16-01-19 11:30:26, David Howells wrote:
> 
> Here's a set of patches that changes how certificates/keys are determined
> to be trusted.  That's currently a two-step process:
> 
>  (1) Up until recently, when an X.509 certificate was parsed - no matter
>      the source - it was judged against the keys in .system_keyring,
>      assuming those keys to be trusted if they have KEY_FLAG_TRUSTED set
>      upon them.
> 
>      This has just been changed such that any key in the .ima_mok keyring
>      may also be used to judge the trustwortiness of a new certificate,
>      whether or not the .ima_mok keyring is meant to be consulted for
>      whatever process is being undertaken.
> 
>      If a certificate is determined to be trustworthy, KEY_FLAG_TRUSTED
>      will be set upon a key it is loaded into (if it is loaded into one),
>      no matter what the key is going to be loaded for.
> 
>  (2) If an X.509 certificate is loaded into a key, then that key - if
>      KEY_FLAG_TRUSTED gets set upon it - can be linked into any keyring
>      with KEY_FLAG_TRUSTED_ONLY set upon it.  This was meant to be the
>      system keyring only, but has been extended to various IMA keyrings.
> 
>      A user can at will link any key marked KEY_FLAG_TRUSTED into any
>      keyring marked KEY_FLAG_TRUSTED_ONLY if the relevant permissions masks
>      permit it.
> 
> These patches change that:
> 
>  (1) Trust becomes a matter of consulting the ring of trusted keys supplied
>      when the trust is evaluated only.
> 
>  (2) Asymmetric keys retain the source certificate signature information
>      for future evaluation rather than discarding it.
> 
>  (3) Every keyring can be supplied with its own manager function to
>      restrict what may be added to that keyring.  This is called whenever a
>      key is to be linked into the keyring to guard against a key being
>      created in one keyring and then linked across.
> 
>      This function is supplied with the keyring and the key type and
>      payload[*] of the key being linked in for use in its evaluation.  It
>      is permitted to use other data also, such as the contents of other
>      keyrings such as the system keyrings.
> 
>      [*] The type and payload are supplied instead of a key because as an
>      	 optimisation this function may be called whilst creating a key and
>      	 so may reject the proposed key between preparse and allocation.
> 
>  (4) A default manager function is provided that permits keys to be
>      restricted to only asymmetric keys that are vouched for by the
>      contents of the system keyring.
> 
>  (5) A key allocation flag, KEY_ALLOC_BYPASS_RESTRICTION, is made available
>      so that the kernel can initialise keyrings with keys that form the
>      root of the trust relationship.
> 
>  (6) KEY_FLAG_TRUSTED and KEY_FLAG_TRUSTED_ONLY are removed, along with
>      key_preparsed_payload::trusted.
> 
> This change also makes it possible for userspace to create a private set of
> trusted keys and then to seal it by setting a manager function where the
> private set is wholly independent of the kernel's trust relationships.
> 
> Further changes in the set involve extracting certain IMA special keyrings
> and making them generally global:
> 
>  (*) .system_keyring is renamed to .builtin_trusted_keys and remains read
>      only.  It carries only keys built in to the kernel.  It may be where
>      UEFI keys should be loaded - though that could better be the new
>      secondary keyring (see below).
> 
>  (*) An optional system blacklist keyring is created to replace the IMA
>      keyring.
> 
>      (*) A 'blacklist' key type is created that may contain a hex string in
>          its description (it carries no payload).  When an X.509
>          certificate is parsed, the system blacklist is searched for a
>          blacklist key that matches the TBS hash of the X.509 certificate
>          and if one is found, the certificate is considered blacklisted.
> 
>      (*) A list of blacklisted hashes can be added to the system blacklist
>          keyring at compile time.  In the future it should also be possible
>          to load this up from such as the UEFI blacklist.
> 
>      (*) Keys can be added to the blacklist keyring by root if the keys are
>      	 signed by a key in the builtin system keyring.  These can then be
>      	 searched for by asymmetric key ID.  This allows the functionality
>      	 of the IMA blacklist keyring to be replicated.
> 
>  	 It might be worth making an asymmetric key subtype that carries no
>  	 data to be used here as the cryptographic material is then just
>  	 dead weight since the IDs are what matter.
> 
>  (*) An optional secondary system keyring (called .secondary_trusted_keys)
>      is added to replace the IMA MOK keyring.
> 
>      (*) Keys can be added to the secondary keyring by root if the keys can
>      	 be vouched for by either ring of system keys.
> 
>  (*) Module signing and kexec only use .builtin_trusted_keys and do not use
>      the new secondary keyring, but they do consult the system blacklist.
> 
>  (*) If the kernel sees a PKCS#7 message with more than one signature, at
>      least one of which is blacklisted, it will permit the message if at
>      least one of the non-blacklisted signature chains is vouched for.  If
>      none are, then EKEYREJECTED will be given.  This error takes priority
>      over giving ENOPKG for unsupported encryption.
> 
> The patches can be found here also:
> 
> 	http://git.kernel.org/cgit/linux/kernel/git/dhowells/linux-fs.git/log/?h=keys-trust
> 
> David
> ---
> David Howells (20):
>       KEYS: Add an alloc flag to convey the builtinness of a key
>       KEYS: Add a system blacklist keyring
>       X.509: Allow X.509 certs to be blacklisted
>       X.509: Don't treat self-signed keys specially
>       KEYS: Generalise system_verify_data() to provide access to internal content
>       PKCS#7: Make trust determination dependent on contents of trust keyring
>       KEYS: Add a facility to restrict new links into a keyring
>       KEYS: Allow authentication data to be stored in an asymmetric key
>       KEYS: Add identifier pointers to public_key_signature struct
>       X.509: Retain the key verification data
>       X.509: Extract signature digest and make self-signed cert checks earlier
>       PKCS#7: Make the signature a pointer rather than embedding it
>       X.509: Move the trust validation code out to its own file
>       KEYS: Generalise x509_request_asymmetric_key()
>       KEYS: Move the point of trust determination to __key_link()
>       KEYS: Remove KEY_FLAG_TRUSTED and KEY_ALLOC_TRUSTED
>       PKCS#7: Handle blacklisted certificates
>       IMA: Use the system blacklist keyring
>       certs: Add a secondary system keyring that can be added to dynamically
>       IMA: Replace the .ima_mok keyring with the secondary system keyring
> 
> 
>  Documentation/security/keys.txt           |   14 +
>  arch/x86/kernel/kexec-bzimage64.c         |   18 --
>  certs/Kconfig                             |   26 ++
>  certs/Makefile                            |    6 +
>  certs/blacklist.c                         |  184 +++++++++++++++++
>  certs/blacklist.h                         |    3 
>  certs/blacklist_hashes.c                  |    6 +
>  certs/blacklist_nohashes.c                |    5 
>  certs/system_keyring.c                    |  141 ++++++++++---
>  crypto/asymmetric_keys/Kconfig            |    1 
>  crypto/asymmetric_keys/Makefile           |    2 
>  crypto/asymmetric_keys/asymmetric_keys.h  |    2 
>  crypto/asymmetric_keys/asymmetric_type.c  |    7 -
>  crypto/asymmetric_keys/mscode_parser.c    |   21 +-
>  crypto/asymmetric_keys/pkcs7_key_type.c   |   66 +++---
>  crypto/asymmetric_keys/pkcs7_parser.c     |   59 +++--
>  crypto/asymmetric_keys/pkcs7_parser.h     |   12 -
>  crypto/asymmetric_keys/pkcs7_trust.c      |   44 ++--
>  crypto/asymmetric_keys/pkcs7_verify.c     |  141 ++++++-------
>  crypto/asymmetric_keys/public_key.c       |   24 ++
>  crypto/asymmetric_keys/public_key.h       |    6 +
>  crypto/asymmetric_keys/public_key_trust.c |  209 +++++++++++++++++++
>  crypto/asymmetric_keys/verify_pefile.c    |   40 +---
>  crypto/asymmetric_keys/verify_pefile.h    |    5 
>  crypto/asymmetric_keys/x509_cert_parser.c |   51 +++--
>  crypto/asymmetric_keys/x509_parser.h      |   13 +
>  crypto/asymmetric_keys/x509_public_key.c  |  318 +++++++++--------------------
>  fs/cifs/cifsacl.c                         |    2 
>  fs/nfs/nfs4idmap.c                        |    2 
>  include/crypto/pkcs7.h                    |    6 -
>  include/crypto/public_key.h               |   35 +--
>  include/keys/asymmetric-subtype.h         |    2 
>  include/keys/asymmetric-type.h            |    8 -
>  include/keys/system_keyring.h             |   52 ++---
>  include/linux/key-type.h                  |    1 
>  include/linux/key.h                       |   39 +++-
>  include/linux/verification.h              |   49 ++++
>  include/linux/verify_pefile.h             |   22 --
>  kernel/module_signing.c                   |    7 -
>  net/dns_resolver/dns_key.c                |    2 
>  net/rxrpc/ar-key.c                        |    4 
>  security/integrity/digsig.c               |   10 +
>  security/integrity/digsig_asymmetric.c    |   18 +-
>  security/integrity/ima/Kconfig            |   18 --
>  security/integrity/ima/Makefile           |    1 
>  security/integrity/ima/ima_mok.c          |   55 -----
>  security/keys/key.c                       |   44 +++-
>  security/keys/keyring.c                   |   26 ++
>  security/keys/persistent.c                |    4 
>  security/keys/process_keys.c              |   16 +
>  security/keys/request_key.c               |    4 
>  security/keys/request_key_auth.c          |    2 
>  52 files changed, 1131 insertions(+), 722 deletions(-)
>  create mode 100644 certs/blacklist.c
>  create mode 100644 certs/blacklist.h
>  create mode 100644 certs/blacklist_hashes.c
>  create mode 100644 certs/blacklist_nohashes.c
>  create mode 100644 crypto/asymmetric_keys/public_key_trust.c
>  create mode 100644 include/linux/verification.h
>  delete mode 100644 include/linux/verify_pefile.h
>  delete mode 100644 security/integrity/ima/ima_mok.c
> 
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