mirror of
https://github.com/torvalds/linux.git
synced 2024-12-25 12:21:37 +00:00
ef8894b0ca
Patch "ima: extend the measurement list to include the file signature" defined a new field called 'sig' and a new template called 'ima-sig'. This patch updates the Documentation/security/IMA-templates.txt. Changelog: - fixed formatting issues (Roberto Sassu) Reported-by: Roberto Sassu <roberto.sassu@polito.it> Signed-off-by: Mimi Zohar <zohar@linux.vnet.ibm.com> Signed-off-by: Roberto Sassu <roberto.sassu@polito.it>
90 lines
4.3 KiB
Plaintext
90 lines
4.3 KiB
Plaintext
IMA Template Management Mechanism
|
|
|
|
|
|
==== INTRODUCTION ====
|
|
|
|
The original 'ima' template is fixed length, containing the filedata hash
|
|
and pathname. The filedata hash is limited to 20 bytes (md5/sha1).
|
|
The pathname is a null terminated string, limited to 255 characters.
|
|
To overcome these limitations and to add additional file metadata, it is
|
|
necessary to extend the current version of IMA by defining additional
|
|
templates. For example, information that could be possibly reported are
|
|
the inode UID/GID or the LSM labels either of the inode and of the process
|
|
that is accessing it.
|
|
|
|
However, the main problem to introduce this feature is that, each time
|
|
a new template is defined, the functions that generate and display
|
|
the measurements list would include the code for handling a new format
|
|
and, thus, would significantly grow over the time.
|
|
|
|
The proposed solution solves this problem by separating the template
|
|
management from the remaining IMA code. The core of this solution is the
|
|
definition of two new data structures: a template descriptor, to determine
|
|
which information should be included in the measurement list; a template
|
|
field, to generate and display data of a given type.
|
|
|
|
Managing templates with these structures is very simple. To support
|
|
a new data type, developers define the field identifier and implement
|
|
two functions, init() and show(), respectively to generate and display
|
|
measurement entries. Defining a new template descriptor requires
|
|
specifying the template format, a string of field identifiers separated
|
|
by the '|' character. While in the current implementation it is possible
|
|
to define new template descriptors only by adding their definition in the
|
|
template specific code (ima_template.c), in a future version it will be
|
|
possible to register a new template on a running kernel by supplying to IMA
|
|
the desired format string. In this version, IMA initializes at boot time
|
|
all defined template descriptors by translating the format into an array
|
|
of template fields structures taken from the set of the supported ones.
|
|
|
|
After the initialization step, IMA will call ima_alloc_init_template()
|
|
(new function defined within the patches for the new template management
|
|
mechanism) to generate a new measurement entry by using the template
|
|
descriptor chosen through the kernel configuration or through the newly
|
|
introduced 'ima_template=' kernel command line parameter. It is during this
|
|
phase that the advantages of the new architecture are clearly shown:
|
|
the latter function will not contain specific code to handle a given template
|
|
but, instead, it simply calls the init() method of the template fields
|
|
associated to the chosen template descriptor and store the result (pointer
|
|
to allocated data and data length) in the measurement entry structure.
|
|
|
|
The same mechanism is employed to display measurements entries.
|
|
The functions ima[_ascii]_measurements_show() retrieve, for each entry,
|
|
the template descriptor used to produce that entry and call the show()
|
|
method for each item of the array of template fields structures.
|
|
|
|
|
|
|
|
==== SUPPORTED TEMPLATE FIELDS AND DESCRIPTORS ====
|
|
|
|
In the following, there is the list of supported template fields
|
|
('<identifier>': description), that can be used to define new template
|
|
descriptors by adding their identifier to the format string
|
|
(support for more data types will be added later):
|
|
|
|
- 'd': the digest of the event (i.e. the digest of a measured file),
|
|
calculated with the SHA1 or MD5 hash algorithm;
|
|
- 'n': the name of the event (i.e. the file name), with size up to 255 bytes;
|
|
- 'd-ng': the digest of the event, calculated with an arbitrary hash
|
|
algorithm (field format: [<hash algo>:]digest, where the digest
|
|
prefix is shown only if the hash algorithm is not SHA1 or MD5);
|
|
- 'n-ng': the name of the event, without size limitations;
|
|
- 'sig': the file signature.
|
|
|
|
|
|
Below, there is the list of defined template descriptors:
|
|
- "ima": its format is 'd|n';
|
|
- "ima-ng" (default): its format is 'd-ng|n-ng';
|
|
- "ima-sig": its format is 'd-ng|n-ng|sig'.
|
|
|
|
|
|
|
|
==== USE ====
|
|
|
|
To specify the template descriptor to be used to generate measurement entries,
|
|
currently the following methods are supported:
|
|
|
|
- select a template descriptor among those supported in the kernel
|
|
configuration ('ima-ng' is the default choice);
|
|
- specify a template descriptor name from the kernel command line through
|
|
the 'ima_template=' parameter.
|