Re: [PATCH] ima: select ima-buf template for buffer measurement
From: Lakshmi Ramasubramanian
Date: Thu Nov 12 2020 - 12:35:32 EST
On 11/11/20 4:58 PM, Mimi Zohar wrote:
Hi Lakshmi,
On Wed, 2020-11-11 at 12:59 -0800, Lakshmi Ramasubramanian wrote:
The default IMA template for measuring buffer should be 'ima-buf' - so
that the measured buffer is correctly included in the IMA measurement
log entry. But the default IMA template used for all policy rules is
the value set for CONFIG_IMA_DEFAULT_TEMPLATE if the policy rule does
not specify a template.
The second sentence defines the current status. The first sentence
describes the problem. I would reverse the sentence order.
^measuring buffer -> buffer measurements
I'll make this change.
IMA does not take into account the template
requirements of different rules when choosing a default template for
a given policy rule. This breaks the buffer measurement if the template
is not provided as part of the rule because the default template could
be different than 'ima-buf'.
Does the above paragraph add anything new? Instead describe the
problem. Perhaps something like:
With the default template format, buffer measurements are added to the
measurement list, but do not include the buffer data, making it
difficult, if not impossible, to validate. Including "ima-buf"
template records in the measurement list by default, should not impact
existing attestation servers without "ima-buf" template support.
This sounds better - I'll make this change.
For example, the following IMA policy rule enables measuring
the command line arguments passed to the new kernel on kexec system call.
measure func=KEXEC_CMDLINE
The IMA template selected should be 'ima-buf' to have the measured
command line arguments included in the IMA measurement log entry.
Instead the default IMA template is selected, which could be different
than 'ima-buf'.
When upstreaming a new type of measurement, including an example
provides how to validate the new template data. Not every patch
description requires an example.
Will remove the above paragraph.
Initialize a global 'ima-buf' template and select that template,
by default, for measuring buffer.
Good.
Signed-off-by: Lakshmi Ramasubramanian <nramas@xxxxxxxxxxxxxxxxxxx>
---
security/integrity/ima/ima.h | 1 +
security/integrity/ima/ima_main.c | 17 +++++------------
security/integrity/ima/ima_policy.c | 2 +-
security/integrity/ima/ima_template.c | 25 +++++++++++++++++++++++++
4 files changed, 32 insertions(+), 13 deletions(-)
diff --git a/security/integrity/ima/ima.h b/security/integrity/ima/ima.h
index 6ebefec616e4..8e8b1e3cb847 100644
--- a/security/integrity/ima/ima.h
+++ b/security/integrity/ima/ima.h
@@ -156,6 +156,7 @@ int template_desc_init_fields(const char *template_fmt,
const struct ima_template_field ***fields,
int *num_fields);
struct ima_template_desc *ima_template_desc_current(void);
+struct ima_template_desc *ima_template_desc_buf(void);
struct ima_template_desc *lookup_template_desc(const char *name);
bool ima_template_has_modsig(const struct ima_template_desc *ima_template);
int ima_restore_measurement_entry(struct ima_template_entry *entry);
diff --git a/security/integrity/ima/ima_main.c b/security/integrity/ima/ima_main.c
index a962b23e0429..3646ae763ba9 100644
--- a/security/integrity/ima/ima_main.c
+++ b/security/integrity/ima/ima_main.c
@@ -413,7 +413,7 @@ int ima_file_mmap(struct file *file, unsigned long prot)
*/
int ima_file_mprotect(struct vm_area_struct *vma, unsigned long prot)
{
- struct ima_template_desc *template;
+ struct ima_template_desc *template = NULL;
struct file *file = vma->vm_file;
char filename[NAME_MAX];
char *pathbuf = NULL;
@@ -802,7 +802,7 @@ void process_buffer_measurement(struct inode *inode, const void *buf, int size,
.filename = eventname,
.buf = buf,
.buf_len = size};
- struct ima_template_desc *template = NULL;
+ struct ima_template_desc *template = ima_template_desc_buf();
struct {
struct ima_digest_data hdr;
char digest[IMA_MAX_DIGEST_SIZE];
@@ -833,16 +833,9 @@ void process_buffer_measurement(struct inode *inode, const void *buf, int size,
pcr = CONFIG_IMA_MEASURE_PCR_IDX;
if (!template) {
- template = lookup_template_desc("ima-buf");
- ret = template_desc_init_fields(template->fmt,
- &(template->fields),
- &(template->num_fields));
- if (ret < 0) {
- pr_err("template %s init failed, result: %d\n",
- (strlen(template->name) ?
- template->name : template->fmt), ret);
- return;
- }
+ ret = -EINVAL;
+ audit_cause = "ima_template_desc_buf";
+ goto out;
Normally a test follows the variable assignment, but in this case, the
check is being deferred in case there isn't a policy rule.
I will initialize the buf template in ima_init_template() per your
comment below. Will move the check for template right after the check
for the IMA policy flag.
if (!ima_policy_flag)
return;
template = ima_template_desc_buf();
if (!template) {
ret = -EINVAL;
audit_cause = "ima_template_desc_buf";
goto out;
}
}
iint.ima_hash = &hash.hdr;
diff --git a/security/integrity/ima/ima_policy.c b/security/integrity/ima/ima_policy.c
index 9b5adeaa47fc..823a0c1379cb 100644
--- a/security/integrity/ima/ima_policy.c
+++ b/security/integrity/ima/ima_policy.c
@@ -628,7 +628,7 @@ int ima_match_policy(struct inode *inode, const struct cred *cred, u32 secid,
struct ima_rule_entry *entry;
int action = 0, actmask = flags | (flags << 1);
- if (template_desc)
+ if (template_desc && !*template_desc)
*template_desc = ima_template_desc_current();
rcu_read_lock();
diff --git a/security/integrity/ima/ima_template.c b/security/integrity/ima/ima_template.c
index 1e89e2d3851f..e53fce2c1610 100644
--- a/security/integrity/ima/ima_template.c
+++ b/security/integrity/ima/ima_template.c
@@ -55,6 +55,7 @@ static const struct ima_template_field supported_fields[] = {
#define MAX_TEMPLATE_NAME_LEN sizeof("d-ng|n-ng|sig|buf|d-modisg|modsig")
static struct ima_template_desc *ima_template;
+static struct ima_template_desc *ima_buf_template;
/**
* ima_template_has_modsig - Check whether template has modsig-related fields.
@@ -252,6 +253,30 @@ struct ima_template_desc *ima_template_desc_current(void)
return ima_template;
}
+struct ima_template_desc *ima_template_desc_buf(void)
+{
+ struct ima_template_desc *template = NULL;
+ int ret = 0;
+
+ if (ima_buf_template)
+ return ima_buf_template;
+
+ ima_init_template_list();
+ template = lookup_template_desc("ima-buf");
+ if (!template)
+ return NULL;
+
+ ret = template_desc_init_fields(template->fmt,
+ &(template->fields),
+ &(template->num_fields));
+ if (ret)
+ return NULL;
Instead of initializing the fields here, maybe it should be done in
ima_init_template()? That would remove the deferred !template test in
process_buffer_measurement() and would also simplify this function.
Will do.
Thanks Mimi.
-lakshmi
+
+ ima_buf_template = template;
+
+ return ima_buf_template;
+}
+
int __init ima_init_template(void)
{
struct ima_template_desc *template = ima_template_desc_current();