Re: [PATCH-v2 3/3] ima: added support for new kernel cmdlineparameter ima_template_fmt

[Mimi Zohar]

On Sat, 2013-12-07 at 10:57 +0100, Roberto Sassu wrote:
> On 12/06/2013 08:36 PM, Mimi Zohar wrote:
> > On Fri, 2013-12-06 at 13:57 +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.
> >>
> >> Changelog:
> >>   - simplified code of ima_template_fmt_setup()
> >>     (Roberto Sassu, suggested by Mimi Zohar)
> >>
> >> Signed-off-by: Roberto Sassu <roberto.sassu@xxxxxxxxx>
> >> Signed-off-by: Mimi Zohar <zohar@xxxxxxxxxxxxxxxxxx>
> >> ---
> >>   Documentation/kernel-parameters.txt      |  4 +++
> >>   Documentation/security/IMA-templates.txt | 29 +++++++++++----------
> >>   security/integrity/ima/ima_template.c    | 43 ++++++++++++++++++++++++++++++++
> >>   3 files changed, 61 insertions(+), 15 deletions(-)
> >>
> >> diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
> >> index 50680a5..bb45dbc 100644
> >> --- a/Documentation/kernel-parameters.txt
> >> +++ b/Documentation/kernel-parameters.txt
> >> @@ -1208,6 +1208,10 @@ 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 a4e102d..7d065f0 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,
> >> @@ -86,4 +83,6 @@ 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 a001477..11adf4a 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 +75,41 @@ 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 = str;
> >> +
> >> +	if (ima_template)
> >> +		return 1;
> >> +
> >> +	while (str_ptr != NULL) {
> >> +		char field_id[IMA_TEMPLATE_FIELD_ID_MAX_LEN];
> >> +		int len = strcspn(str_ptr, "|");
> >> +
> >> +		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, 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 = (str_ptr[len] == '|') ? str_ptr + len + 1 : NULL;
> >
> > Personally, I think it would be cleaner to use a 'for' loop.  Something
> > like: for (bufp = buf; bufp < bufend; bufp += len + 1)
> >
> 
> Hi Mimi
> 
> this solution will not work because it does not properly
> handle a string like 'validfield|'. Indeed, at the second
> iteration, you already reached the end of the string and
> exit without detecting a field identifier of length zero.

If this is the only issue, you could check the last character, before
entering the loop.

Mimi

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