linux.git/security/integrity/ima/ima_template_lib.c, branch v5.19

ima: fix violation measurement list record

2022-07-07T02:31:52+00:00

Although the violation digest in the IMA measurement list is always
zeroes, the size of the digest should be based on the hash algorithm.
Until recently the hash algorithm was hard coded to sha1.  Fix the
violation digest size included in the IMA measurement list.

This is just a cosmetic change which should not affect attestation.

Reported-by: Stefan Berger 
Fixes: 09091c44cb73 ("ima: use IMA default hash algorithm for integrity violations")
Tested-by: Stefan Berger 
Signed-off-by: Mimi Zohar

ima: support fs-verity file digest based version 3 signatures

2022-05-05T21:41:51+00:00

IMA may verify a file's integrity against a "good" value stored in the
'security.ima' xattr or as an appended signature, based on policy.  When
the "good value" is stored in the xattr, the xattr may contain a file
hash or signature.  In either case, the "good" value is preceded by a
header.  The first byte of the xattr header indicates the type of data
- hash, signature - stored in the xattr.  To support storing fs-verity
signatures in the 'security.ima' xattr requires further differentiating
the fs-verity signature from the existing IMA signature.

In addition the signatures stored in 'security.ima' xattr, need to be
disambiguated.  Instead of directly signing the fs-verity digest, a new
signature format version 3 is defined as the hash of the ima_file_id
structure, which identifies the type of signature and the digest.

The IMA policy defines "which" files are to be measured, verified, and/or
audited.  For those files being verified, the policy rules indicate "how"
the file should be verified.  For example to require a file be signed,
the appraise policy rule must include the 'appraise_type' option.

	appraise_type:= [imasig] | [imasig|modsig] | [sigv3]
           where 'imasig' is the original or signature format v2 (default),
           where 'modsig' is an appended signature,
           where 'sigv3' is the signature format v3.

The policy rule must also indicate the type of digest, if not the IMA
default, by first specifying the digest type:

	digest_type:= [verity]

The following policy rule requires fsverity signatures.  The rule may be
constrained, for example based on a fsuuid or LSM label.

      appraise func=BPRM_CHECK digest_type=verity appraise_type=sigv3

Acked-by: Stefan Berger 
Signed-off-by: Mimi Zohar

ima: permit fsverity's file digests in the IMA measurement list

2022-05-05T15:49:13+00:00

Permit fsverity's file digest (a hash of struct fsverity_descriptor) to
be included in the IMA measurement list, based on the new measurement
policy rule 'digest_type=verity' option.

To differentiate between a regular IMA file hash from an fsverity's
file digest, use the new d-ngv2 format field included in the ima-ngv2
template.

The following policy rule requires fsverity file digests and specifies
the new 'ima-ngv2' template, which contains the new 'd-ngv2' field.  The
policy rule may be constrained, for example based on a fsuuid or LSM
label.

measure func=FILE_CHECK digest_type=verity template=ima-ngv2

Acked-by: Stefan Berger 
Signed-off-by: Mimi Zohar

ima: define a new template field named 'd-ngv2' and templates

2022-05-05T15:49:13+00:00

In preparation to differentiate between unsigned regular IMA file
hashes and fs-verity's file digests in the IMA measurement list,
define a new template field named 'd-ngv2'.

Also define two new templates named 'ima-ngv2' and 'ima-sigv2', which
include the new 'd-ngv2' field.

Signed-off-by: Mimi Zohar

ima: use IMA default hash algorithm for integrity violations

2022-05-01T20:39:10+00:00

Integrity file violations - ToM/ToU, open writers - are recorded in the IMA
measurement list, containing 0x00's in both the template data and file data
hash fields, but 0xFF's are actually extended into TPM PCRs.  Although the
original 'ima' template data field ('d') is limited to 20 bytes, the 'd-ng'
template digest field is not.

The violation file data hash template field ('d-ng') is unnecessarily hard
coded to SHA1.  Instead of simply replacing the hard coded SHA1 hash
algorithm with a larger hash algorithm, use the hash algorithm as defined
in "ima_hash_algo".  ima_hash_algo is set to either the Kconfig IMA default
hash algorithm or as defined on the boot command line (ima_hash=).

Including a non-SHA1 file data hash algorithm in the 'd-ng' field of
violations is a cosmetic change.  The template data hash field, which is
extended into the TPM PCRs, is not affected by this change and should not
affect attestation of the IMA measurement list.

Tested-by: Stefan Berger 
Signed-off-by: Mimi Zohar

ima: fix 'd-ng' comments and documentation

2022-05-01T20:38:10+00:00

Initially the 'd-ng' template field did not prefix the digest with either
"md5" or "sha1" hash algorithms.  Prior to being upstreamed this changed,
but the comments and documentation were not updated.  Fix the comments
and documentation.

Fixes: 4d7aeee73f53 ("ima: define new template ima-ng and template fields d-ng and n-ng")
Reported-by: Eric Biggers 
Reviewed-by: Stefan Berger 
Signed-off-by: Mimi Zohar

ima: define ima_max_digest_data struct without a flexible array variable

2022-02-15T16:52:06+00:00

To support larger hash digests in the 'iint' cache, instead of defining
the 'digest' field as the maximum digest size, the 'digest' field was
defined as a flexible array variable.  The "ima_digest_data" struct was
wrapped inside a local structure with the maximum digest size.  But
before adding the record to the iint cache, memory for the exact digest
size was dynamically allocated.

The original reason for defining the 'digest' field as a flexible array
variable is still valid for the 'iint' cache use case.  Instead of
wrapping the 'ima_digest_data' struct in a local structure define
'ima_max_digest_data' struct.

Reviewed-by: Stefan Berger 
Signed-off-by: Mimi Zohar

ima: Fix trivial typos in the comments

2022-02-15T16:10:03+00:00

There are a few minor typos in the comments. Fix these.

Signed-off-by: Austin Kim 
Signed-off-by: Mimi Zohar

ima: Fix fall-through warning for Clang

2021-06-09T03:33:48+00:00

In preparation to enable -Wimplicit-fallthrough for Clang, fix a
fall-through warning by explicitly adding a break statement instead
of just letting the code fall through to the next case.

Link: https://github.com/KSPP/linux/issues/115
Signed-off-by: Gustavo A. R. Silva 
Reviewed-by: Kees Cook 
Signed-off-by: Mimi Zohar

ima/evm: Fix type mismatch

2021-06-08T20:29:10+00:00

The endianness of a variable written to the measurement list cannot be
determined at compile time, as it depends on the value of the
ima_canonical_fmt global variable (set through a kernel option with the
same name if the machine is big endian).

If ima_canonical_fmt is false, the endianness of a variable is the same as
the machine; if ima_canonical_fmt is true, the endianness is little endian.
The warning arises due to this type of instruction:

var = cpu_to_leXX(var)

which tries to assign a value in little endian to a variable with native
endianness (little or big endian).

Given that the variables set with this instruction are not used in any
operation but just written to a buffer, it is safe to force the type of the
value being set to be the same of the type of the variable with:

var = (__force )cpu_to_leXX(var)

Reported-by: kernel test robot 
Signed-off-by: Roberto Sassu 
Signed-off-by: Mimi Zohar