[PATCH v3 00/13] security: digest_cache LSM

From: Roberto Sassu
Date: Fri Feb 09 2024 - 09:10:18 EST

From: Roberto Sassu <roberto.sassu@xxxxxxxxxx>

Introduce the digest_cache LSM, whose purpose is to deliver reference
digest values to integrity providers, such as IMA and IPE, abstracting to
them how those digests where extracted from the respective data source.

The major benefit is the ability to use the vaste amount of digests already
provided (and likely signed) by software vendors, without needing them to
adapt their format to the one understood by the integrity provider.

IMA and IPE can immediately interface with the digest_cache LSM and query
the digest of an accessed file. If the digest is found, it means that the
file is coming from the software vendor and not modified. If not, the file
might have been corrupted. Each integrity provider decides how to handle
this situation.

The second major benefit is performance improvement. Since the digest_cache
LSM has the ability to extract many digests from a single data source, it
means that it has less signatures to verify compared to the approach of
verifying individual file signatures (IMA appraisal). Preliminary tests
have shown a speedup of IMA appraisal of about 65% for sequential read, and
45% for parallel read.

This patch set has as prerequisites the file_release LSM hook (to be
introduced with the move of IMA/EVM to the LSM infrastructure), and
support for PGP keys, which is still unclear how it should be done.

The IMA integration patch set will be introduced separately. Also a PoC
based on the current version of IPE can be provided.

- Include the TLV parser in this patch set (from user asymmetric keys and
- Move from IMA and make an independent LSM
- Remove IMA-specific stuff from this patch set
- Add per algorithm hash table
- Expect all digest lists to be in the same directory and allow changing
the default directory
- Support digest lookup on directories, when there is no
security.digest_list xattr
- Add seq num to digest list file name, to impose ordering on directory
- Add a new data type DIGEST_LIST_ENTRY_DATA for the nested data in the
tlv digest list format
- Add the concept of verification data attached to digest caches
- Add the reset mechanism to track changes on digest lists and directory
containing the digest lists
- Add kernel selftests

- Add documentation in Documentation/security/integrity-digest-cache.rst
- Pass the mask of IMA actions to digest_cache_alloc()
- Add a reference count to the digest cache
- Remove the path parameter from digest_cache_get(), and rely on the
reference count to avoid the digest cache disappearing while being used
- Rename the dentry_to_check parameter of digest_cache_get() to dentry
- Rename digest_cache_get() to digest_cache_new() and add
digest_cache_get() to set the digest cache in the iint of the inode for
which the digest cache was requested
- Add dig_owner and dig_user to the iint, to distinguish from which inode
the digest cache was created from, and which is using it; consequently it
makes the digest cache usable to measure/appraise other digest caches
(support not yet enabled)
- Add dig_owner_mutex and dig_user_mutex to serialize accesses to dig_owner
and dig_user until they are initialized
- Enforce strong synchronization and make the contenders wait until
dig_owner and dig_user are assigned to the iint the first time
- Move checking IMA actions on the digest list earlier, and fail if no
action were performed (digest cache not usable)
- Remove digest_cache_put(), not needed anymore with the introduction of
the reference count
- Fail immediately in digest_cache_lookup() if the digest algorithm is
not set in the digest cache
- Use 64 bit mask for IMA actions on the digest list instead of 8 bit
- Return NULL in the inline version of digest_cache_get()
- Use list_add_tail() instead of list_add() in the iterator
- Copy the digest list path to a separate buffer in digest_cache_iter_dir()
- Use digest list parsers verified with Frama-C
- Explicitly disable (for now) the possibility in the IMA policy to use the
digest cache to measure/appraise other digest lists
- Replace exit(<value>) with return <value> in manage_digest_lists.c

Roberto Sassu (13):
lib: Add TLV parser
security: Introduce the digest_cache LSM
digest_cache: Add securityfs interface
digest_cache: Add hash tables and operations
digest_cache: Populate the digest cache from a digest list
digest_cache: Parse tlv digest lists
digest_cache: Parse rpm digest lists
digest_cache: Add management of verification data
digest_cache: Add support for directories
digest cache: Prefetch digest lists if requested
digest_cache: Reset digest cache on file/directory change
selftests/digest_cache: Add selftests for digest_cache LSM
docs: Add documentation of the digest_cache LSM

Documentation/security/digest_cache.rst | 900 ++++++++++++++++++
Documentation/security/index.rst | 1 +
include/linux/digest_cache.h | 89 ++
include/linux/kernel_read_file.h | 1 +
include/linux/tlv_parser.h | 28 +
include/uapi/linux/lsm.h | 1 +
include/uapi/linux/tlv_digest_list.h | 72 ++
include/uapi/linux/tlv_parser.h | 59 ++
include/uapi/linux/xattr.h | 6 +
lib/Kconfig | 3 +
lib/Makefile | 3 +
lib/tlv_parser.c | 214 +++++
lib/tlv_parser.h | 17 +
security/Kconfig | 11 +-
security/Makefile | 1 +
security/digest_cache/Kconfig | 34 +
security/digest_cache/Makefile | 11 +
security/digest_cache/dir.c | 245 +++++
security/digest_cache/htable.c | 268 ++++++
security/digest_cache/internal.h | 259 +++++
security/digest_cache/main.c | 545 +++++++++++
security/digest_cache/modsig.c | 66 ++
security/digest_cache/parsers/parsers.h | 15 +
security/digest_cache/parsers/rpm.c | 223 +++++
security/digest_cache/parsers/tlv.c | 299 ++++++
security/digest_cache/populate.c | 163 ++++
security/digest_cache/reset.c | 168 ++++
security/digest_cache/secfs.c | 87 ++
security/digest_cache/verif.c | 119 +++
security/security.c | 3 +-
tools/testing/selftests/Makefile | 1 +
.../testing/selftests/digest_cache/.gitignore | 3 +
tools/testing/selftests/digest_cache/Makefile | 23 +
.../testing/selftests/digest_cache/all_test.c | 706 ++++++++++++++
tools/testing/selftests/digest_cache/common.c | 79 ++
tools/testing/selftests/digest_cache/common.h | 131 +++
.../selftests/digest_cache/common_user.c | 47 +
.../selftests/digest_cache/common_user.h | 17 +
tools/testing/selftests/digest_cache/config | 1 +
.../selftests/digest_cache/generators.c | 248 +++++
.../selftests/digest_cache/generators.h | 19 +
.../selftests/digest_cache/testmod/Makefile | 16 +
.../selftests/digest_cache/testmod/kern.c | 499 ++++++++++
.../selftests/lsm/lsm_list_modules_test.c | 3 +
45 files changed, 5714 insertions(+), 6 deletions(-)
create mode 100644 Documentation/security/digest_cache.rst
create mode 100644 include/linux/digest_cache.h
create mode 100644 include/linux/tlv_parser.h
create mode 100644 include/uapi/linux/tlv_digest_list.h
create mode 100644 include/uapi/linux/tlv_parser.h
create mode 100644 lib/tlv_parser.c
create mode 100644 lib/tlv_parser.h
create mode 100644 security/digest_cache/Kconfig
create mode 100644 security/digest_cache/Makefile
create mode 100644 security/digest_cache/dir.c
create mode 100644 security/digest_cache/htable.c
create mode 100644 security/digest_cache/internal.h
create mode 100644 security/digest_cache/main.c
create mode 100644 security/digest_cache/modsig.c
create mode 100644 security/digest_cache/parsers/parsers.h
create mode 100644 security/digest_cache/parsers/rpm.c
create mode 100644 security/digest_cache/parsers/tlv.c
create mode 100644 security/digest_cache/populate.c
create mode 100644 security/digest_cache/reset.c
create mode 100644 security/digest_cache/secfs.c
create mode 100644 security/digest_cache/verif.c
create mode 100644 tools/testing/selftests/digest_cache/.gitignore
create mode 100644 tools/testing/selftests/digest_cache/Makefile
create mode 100644 tools/testing/selftests/digest_cache/all_test.c
create mode 100644 tools/testing/selftests/digest_cache/common.c
create mode 100644 tools/testing/selftests/digest_cache/common.h
create mode 100644 tools/testing/selftests/digest_cache/common_user.c
create mode 100644 tools/testing/selftests/digest_cache/common_user.h
create mode 100644 tools/testing/selftests/digest_cache/config
create mode 100644 tools/testing/selftests/digest_cache/generators.c
create mode 100644 tools/testing/selftests/digest_cache/generators.h
create mode 100644 tools/testing/selftests/digest_cache/testmod/Makefile
create mode 100644 tools/testing/selftests/digest_cache/testmod/kern.c