[PATCH v7 00/16] EVM

Mimi Zohar
2011-06-29T19:51:26Z

Discretionary Access Control(DAC) and Mandatory Access Control(MAC) can
protect the integrity of a running system from unauthorized changes. When
these protections are not running, such as when booting a malicious OS,
mounting the disk under a different operating system, or physically moving
the disk to another system, an "offline" attack is free to read and write
file data/metadata.

Extended Verification Module(EVM) detects offline tampering of the security
extended attributes (e.g. security.selinux, security.SMACK64, security.ima),
which is the basis for LSM permission decisions and, with the IMA-appraisal
patchset, integrity appraisal decisions. This patchset provides the framework
and an initial method to detect offline tampering of the security extended
attributes. The initial method maintains an HMAC-sha1 across a set of
security extended attributes, storing the HMAC as the extended attribute
'security.evm'. To verify the integrity of an extended attribute, EVM exports
evm_verifyxattr(), which re-calculates the HMAC and compares it with the
version stored in 'security.evm'. Other methods of validating the integrity
of a file's metadata will be posted separately (eg. EVM-digital-signatures).

Although an offline attack can bypass DAC/MAC protection mechanisms and write
file data/metadata, if the disk, or VM, is subsequently remounted under the
EVM + DAC/MAC (+ IMA-appraisal) protected OS, then the TPM-calculated HMAC of
the file's metadata won't be valid. Therefore, IMA + MAC/DAC + EVM
(+ IMA-appraisal) can protect system integrity online, detect offline tampering,
and prevent tampered files from being accessed.

While this patchset does authenticate the security xattrs, and
cryptographically binds them to the inode, coming extensions will bind other
directory and inode metadata for more complete protection. To help simplify
the review and upstreaming process, each extension will be posted separately
(eg. IMA-appraisal, IMA-digital-signatures (including module checking),
IMA-appraisal-directory). For a general overview of the proposed Linux
integrity subsystem, refer to Dave Safford's whitepaper:
http://downloads.sf.net/project/linux-ima/linux-ima/Integrity_overview.pdf.

Much appreciation to Dave Hansen, Serge Hallyn, and Matt Helsley for
reviewing the original patches.

Changes from v6:
- Changed the security_inode_init_security API to write the security xattr,
by calling an fs specific callback.
- Moved the evm_inode_post_init() calls, which calculate the EVM xattr, from
each fs to security_inode_init_security.
- Renamed evm_inode_post_init_security() to evm_inode_init_security().
- Renamed the boot parameter evm_mode=' to 'evm='.

Changes from v5:
- defined 'struct evm_ima_xattr_data',
removed MAX_DIGEST_SIZE and evm_hmac_size definitions
- check for key failures and errors earlier
- other minor changes enumerated in individual patch descriptions

Changes from v4:
- Added evm_inode_post_init calls for: btrfs, gfs2, jffs2, jfs, and xfs.
- Prevent an invalid security.evm xattr from being updated.
- evm_verifyxattr() performance improvement (Dmitry Kasatkin)
- Fixed evm_verify_hmac() to be fail safe (Dmitry Kasatkin)
- Additional naming change generalizations in preparation for other methods
of integrity authentication. (Dmitry Kasatkin)

Mimi Zohar
David Safford

Dmitry Kasatkin (5):
evm: add support for different security.evm data types
evm: crypto hash replaced by shash
evm: additional parameter to pass integrity cache entry 'iint'
evm: evm_verify_hmac must not return INTEGRITY_UNKNOWN
evm: replace hmac_status with evm_status

Mimi Zohar (11):
security: new security_inode_init_security API adds function callback
integrity: move ima inode integrity data management
xattr: define vfs_getxattr_alloc and vfs_xattr_cmp
evm: re-release
security: imbed evm calls in security hooks
evm: evm_inode_post_removexattr
evm: imbed evm_inode_post_setattr
evm: add evm_inode_init_security to initialize new files
evm: call evm_inode_init_security from security_inode_init_security
evm: permit only valid security.evm xattrs to be updated
evm: add evm_inode_setattr to prevent updating an invalid
security.evm

Documentation/ABI/testing/evm | 23 ++
Documentation/kernel-parameters.txt | 6 +
fs/attr.c | 5 +-
fs/btrfs/xattr.c | 52 +++---
fs/ext2/xattr_security.c | 34 ++--
fs/ext3/xattr_security.c | 36 ++--
fs/ext4/xattr_security.c | 36 ++--
fs/gfs2/inode.c | 38 ++--
fs/jffs2/security.c | 37 ++--
fs/jfs/xattr.c | 57 +++---
fs/ocfs2/xattr.c | 38 +++--
fs/reiserfs/xattr_security.c | 4 +-
fs/xattr.c | 63 ++++++-
fs/xfs/linux-2.6/xfs_iops.c | 39 ++--
include/linux/evm.h | 92 +++++++++
include/linux/ima.h | 13 --
include/linux/integrity.h | 38 ++++
include/linux/security.h | 17 +-
include/linux/xattr.h | 14 ++-
mm/shmem.c | 4 +-
security/Kconfig | 2 +-
security/Makefile | 4 +-
security/integrity/Kconfig | 7 +
security/integrity/Makefile | 12 +
security/integrity/evm/Kconfig | 12 +
security/integrity/evm/Makefile | 6 +
security/integrity/evm/evm.h | 38 ++++
security/integrity/evm/evm_crypto.c | 216 ++++++++++++++++++++
security/integrity/evm/evm_main.c | 384 +++++++++++++++++++++++++++++++++++
security/integrity/evm/evm_secfs.c | 108 ++++++++++
security/integrity/iint.c | 171 ++++++++++++++++
security/integrity/ima/Kconfig | 1 +
security/integrity/ima/Makefile | 2 +-
security/integrity/ima/ima.h | 29 +--
security/integrity/ima/ima_api.c | 7 +-
security/integrity/ima/ima_iint.c | 169 ---------------
security/integrity/ima/ima_main.c | 12 +-
security/integrity/integrity.h | 47 +++++
security/security.c | 71 ++++++-
39 files changed, 1537 insertions(+), 407 deletions(-)
create mode 100644 Documentation/ABI/testing/evm
create mode 100644 include/linux/evm.h
create mode 100644 include/linux/integrity.h
create mode 100644 security/integrity/Kconfig
create mode 100644 security/integrity/Makefile
create mode 100644 security/integrity/evm/Kconfig
create mode 100644 security/integrity/evm/Makefile
create mode 100644 security/integrity/evm/evm.h
create mode 100644 security/integrity/evm/evm_crypto.c
create mode 100644 security/integrity/evm/evm_main.c
create mode 100644 security/integrity/evm/evm_secfs.c
create mode 100644 security/integrity/iint.c
delete mode 100644 security/integrity/ima/ima_iint.c
create mode 100644 security/integrity/integrity.h

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1.7.3.4