Re: [RFC][PATCH 4/4] ima: added support for new kernel cmdline parameter ima_template_fmt

[Roberto Sassu <roberto.sassu@polito.it>]

On 12/04/2013 10:05 PM, Mimi Zohar wrote:
> On Thu, 2013-11-07 at 15:00 +0100, Roberto Sassu wrote:
>> This patch allows users to provide a custom template format through the
>> new kernel command line parameter 'ima_template_fmt'. If the supplied
>> format is not valid, IMA uses the default template descriptor.
>>
>> Signed-off-by: Roberto Sassu <roberto.sassu@polito.it>
>> ---
>>   Documentation/kernel-parameters.txt      |  4 +++
>>   Documentation/security/IMA-templates.txt | 29 +++++++++---------
>>   security/integrity/ima/ima_template.c    | 50 ++++++++++++++++++++++++++++++++
>>   3 files changed, 68 insertions(+), 15 deletions(-)
>>
>> diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
>> index 1e8761c..27b14b2 100644
>> --- a/Documentation/kernel-parameters.txt
>> +++ b/Documentation/kernel-parameters.txt
>> @@ -1199,6 +1199,10 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
>>   			Formats: { "ima" | "ima-ng" }
>>   			Default: "ima-ng"
>>
>> +	ima_template_fmt=
>> +	                [IMA] Define a custom template format.
>> +			Format: { "field1|...|fieldN" }
>> +
>>   	init=		[KNL]
>>   			Format: <full_path>
>>   			Run specified binary instead of /sbin/init as init
>> diff --git a/Documentation/security/IMA-templates.txt b/Documentation/security/IMA-templates.txt
>> index a777e5f..08ea2da 100644
>> --- a/Documentation/security/IMA-templates.txt
>> +++ b/Documentation/security/IMA-templates.txt
>> @@ -27,25 +27,22 @@ 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.
>> +specifying the template format (a string of field identifiers separated
>> +by the '|' character) through the 'ima_template_fmt' kernel command line
>> +parameter. At boot time, IMA initializes 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.
>> +introduced 'ima_template' and 'ima_template_fmt' kernel command line parameters.
>> +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,
>> @@ -84,4 +81,6 @@ 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.
>> +   the 'ima_template=' parameter;
>> + - register a new template descriptor with custom format through the kernel
>> +   command line parameter 'ima_template_fmt='.
>> diff --git a/security/integrity/ima/ima_template.c b/security/integrity/ima/ima_template.c
>> index bb33576..5a95d06 100644
>> --- a/security/integrity/ima/ima_template.c
>> +++ b/security/integrity/ima/ima_template.c
>> @@ -21,6 +21,7 @@ static struct ima_template_desc defined_templates[] = {
>>   	{.name = IMA_TEMPLATE_IMA_NAME, .fmt = IMA_TEMPLATE_IMA_FMT},
>>   	{.name = "ima-ng",.fmt = "d-ng|n-ng"},
>>   	{.name = "ima-sig",.fmt = "d-ng|n-ng|sig"},
>> +	{.name = "",.fmt = ""},	/* placeholder for a custom format */
>>   };
>>
>>   static struct ima_template_field supported_fields[] = {
>> @@ -38,12 +39,16 @@ static struct ima_template_field supported_fields[] = {
>>
>>   static struct ima_template_desc *ima_template;
>>   static struct ima_template_desc *lookup_template_desc(const char *name);
>> +static struct ima_template_field *lookup_template_field(const char *field_id);
>>
>>   static int __init ima_template_setup(char *str)
>>   {
>>   	struct ima_template_desc *template_desc;
>>   	int template_len = strlen(str);
>>
>> +	if (ima_template)
>> +		return 1;
>> +
>>   	/*
>>   	 * Verify that a template with the supplied name exists.
>>   	 * If not, use CONFIG_IMA_DEFAULT_TEMPLATE.
>> @@ -70,6 +75,48 @@ static int __init ima_template_setup(char *str)
>>   }
>>   __setup("ima_template=", ima_template_setup);
>>
>> +static int __init ima_template_fmt_setup(char *str)
>> +{
>> +	int num_templates = ARRAY_SIZE(defined_templates);
>> +	char *str_ptr_start = str;
>> +	char *str_ptr_end = str_ptr_start;
>> +
>> +	if (ima_template)
>> +		return 1;
>> +
>> +	while (str_ptr_start != NULL) {
>> +		char field_id[IMA_TEMPLATE_FIELD_ID_MAX_LEN];
>> +		int len;
>> +
>> +		str_ptr_end = strpbrk(str_ptr_start, "|");
>> +		if (str_ptr_end == NULL)
>> +			len = str + strlen(str) - str_ptr_start;
>> +		else
>> +			len = str_ptr_end++ - str_ptr_start;
>> +
>> +		if (len >= IMA_TEMPLATE_FIELD_ID_MAX_LEN) {
>> +			pr_err("IMA: field too long, using template %s\n",
>> +			       CONFIG_IMA_DEFAULT_TEMPLATE);
>> +			return 1;
>> +		}
>> +
>> +		memcpy(field_id, str_ptr_start, len);
>> +		field_id[len] = '\0';
>> +		if (lookup_template_field(field_id) == NULL) {
>> +			pr_err("IMA: field '%s' not found, using template %s\n",
>> +			       field_id, CONFIG_IMA_DEFAULT_TEMPLATE);
>> +			return 1;
>> +		}
>> +
>> +		str_ptr_start = str_ptr_end;
>> +	}
>> +
>
> Roberto, looking this over again, I think this can be simplified by
> using strsep().
>

Hi Mimi

yes, the code can be simplified. However, I did not use strsep()
to avoid that this function modifies the kernel command line
(it replaces the passed separator character with '\0').
Since the custom format string is parsed again later, I also
have to revert changes made by strsep().

Thanks

Roberto Sassu


> Mimi
>
>> +	defined_templates[num_templates - 1].fmt = str;
>> +	ima_template = defined_templates + num_templates - 1;
>> +	return 1;
>> +}
>> +__setup("ima_template_fmt=", ima_template_fmt_setup);
>> +
>>   static struct ima_template_desc *lookup_template_desc(const char *name)
>>   {
>>   	int i;
>> @@ -160,6 +207,9 @@ static int init_defined_templates(void)
>>   	for (i = 0; i < ARRAY_SIZE(defined_templates); i++) {
>>   		struct ima_template_desc *template = &defined_templates[i];
>>
>> +		if (strlen(template->fmt) == 0)
>> +			continue;
>> +
>>   		result = template_desc_init_fields(template->fmt,
>>   						   &(template->fields),
>>   						   &(template->num_fields));
>
>