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

From: Mimi Zohar
Date: Thu Dec 05 2013 - 07:15:48 EST

On Thu, 2013-12-05 at 09:49 +0100, Roberto Sassu wrote:
> 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@xxxxxxxxx>
> >> ---
> >> 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().

Somehow the code needs to be simplified and cleaned up. For example,
str_ptr_start/end need to be renamed to something simpler, like
field/field_end or token/token_end. (Refer to Documentation/CodingStyle
chapter 4 for variable naming style.) Perhaps, instead of using
strsep(), write a function to return a pointer to the field and field
length.

thanks,

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));
> >
> >
>
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