path: root/security
diff options
authorEric Paris <eparis@redhat.com>2009-05-21 15:47:06 -0400
committerJames Morris <jmorris@namei.org>2009-05-22 09:31:20 +1000
commit5789ba3bd0a3cd20df5980ebf03358f2eb44fd67 (patch)
tree4ad5dc0496f0d6bc06e9614ff5edbc0400fcdb5d /security
parentc5642f4bbae30122beb696e723f6da273caa570e (diff)
IMA: Minimal IMA policy and boot param for TCB IMA policy
The IMA TCB policy is dangerous. A normal use can use all of a system's memory (which cannot be freed) simply by building and running lots of executables. The TCB policy is also nearly useless because logging in as root often causes a policy violation when dealing with utmp, thus rendering the measurements meaningless. There is no good fix for this in the kernel. A full TCB policy would need to be loaded in userspace using LSM rule matching to get both a protected and useful system. But, if too little is measured before userspace can load a real policy one again ends up with a meaningless set of measurements. One option would be to put the policy load inside the initrd in order to get it early enough in the boot sequence to be useful, but this runs into trouble with the LSM. For IMA to measure the LSM policy and the LSM policy loading mechanism it needs rules to do so, but we already talked about problems with defaulting to such broad rules.... IMA also depends on the files being measured to be on an FS which implements and supports i_version. Since the only FS with this support (ext4) doesn't even use it by default it seems silly to have any IMA rules by default. This should reduce the performance overhead of IMA to near 0 while still letting users who choose to configure their machine as such to inclue the ima_tcb kernel paramenter and get measurements during boot before they can load a customized, reasonable policy in userspace. Signed-off-by: Eric Paris <eparis@redhat.com> Acked-by: Mimi Zohar <zohar@us.ibm.com> Signed-off-by: James Morris <jmorris@namei.org>
Diffstat (limited to 'security')
1 files changed, 27 insertions, 3 deletions
diff --git a/security/integrity/ima/ima_policy.c b/security/integrity/ima/ima_policy.c
index 31d677f7c65..4719bbf1641 100644
--- a/security/integrity/ima/ima_policy.c
+++ b/security/integrity/ima/ima_policy.c
@@ -45,9 +45,17 @@ struct ima_measure_rule_entry {
-/* Without LSM specific knowledge, the default policy can only be
+ * Without LSM specific knowledge, the default policy can only be
* written in terms of .action, .func, .mask, .fsmagic, and .uid
+ * The minimum rule set to allow for full TCB coverage. Measures all files
+ * opened or mmap for exec and everything read by root. Dangerous because
+ * normal users can easily run the machine out of memory simply building
+ * and running executables.
+ */
static struct ima_measure_rule_entry default_rules[] = {
{.action = DONT_MEASURE,.fsmagic = PROC_SUPER_MAGIC,.flags = IMA_FSMAGIC},
{.action = DONT_MEASURE,.fsmagic = SYSFS_MAGIC,.flags = IMA_FSMAGIC},
@@ -59,6 +67,8 @@ static struct ima_measure_rule_entry default_rules[] = {
.flags = IMA_FUNC | IMA_MASK},
{.action = MEASURE,.func = BPRM_CHECK,.mask = MAY_EXEC,
.flags = IMA_FUNC | IMA_MASK},
+ {.action = MEASURE,.func = PATH_CHECK,.mask = MAY_READ,.uid = 0,
+ .flags = IMA_FUNC | IMA_MASK | IMA_UID},
static LIST_HEAD(measure_default_rules);
@@ -67,6 +77,14 @@ static struct list_head *ima_measure;
static DEFINE_MUTEX(ima_measure_mutex);
+static bool ima_use_tcb __initdata;
+static int __init default_policy_setup(char *str)
+ ima_use_tcb = 1;
+ return 1;
+__setup("ima_tcb", default_policy_setup);
* ima_match_rules - determine whether an inode matches the measure rule.
* @rule: a pointer to a rule
@@ -162,9 +180,15 @@ int ima_match_policy(struct inode *inode, enum ima_hooks func, int mask)
void ima_init_policy(void)
- int i;
+ int i, entries;
+ /* if !ima_use_tcb set entries = 0 so we load NO default rules */
+ if (ima_use_tcb)
+ entries = ARRAY_SIZE(default_rules);
+ else
+ entries = 0;
- for (i = 0; i < ARRAY_SIZE(default_rules); i++)
+ for (i = 0; i < entries; i++)
list_add_tail(&default_rules[i].list, &measure_default_rules);
ima_measure = &measure_default_rules;