[PATCH v2 2/3] IMA: add policy to support measuring critical data from kernel components
Mimi Zohar
zohar at linux.ibm.com
Mon Aug 24 22:46:41 UTC 2020
On Fri, 2020-08-21 at 11:21 -0700, Tushar Sugandhi wrote:
> There would be several candidate kernel components suitable for IMA
> measurement. Not all of them would have support for IMA measurement.
> Also, system administrators may not want to measure data for all of
> them, even when they support IMA measurement. An IMA policy specific
> to various kernel components is needed to measure their respective
> critical data.
>
> Add a new IMA policy CRITICAL_DATA+data_sources to support measuring
> various critical kernel components. This policy would enable the
> system administrators to limit the measurement to the components,
> if the components support IMA measurement.
>
> Signed-off-by: Tushar Sugandhi <tusharsu at linux.microsoft.com>
> ---
> Documentation/ABI/testing/ima_policy | 6 ++-
> security/integrity/ima/ima.h | 1 +
> security/integrity/ima/ima_api.c | 2 +-
> security/integrity/ima/ima_policy.c | 62 +++++++++++++++++++++++++---
> 4 files changed, 63 insertions(+), 8 deletions(-)
>
> diff --git a/Documentation/ABI/testing/ima_policy b/Documentation/ABI/testing/ima_policy
> index cd572912c593..a0dd0f108555 100644
> --- a/Documentation/ABI/testing/ima_policy
> +++ b/Documentation/ABI/testing/ima_policy
> @@ -29,7 +29,7 @@ Description:
> base: func:= [BPRM_CHECK][MMAP_CHECK][CREDS_CHECK][FILE_CHECK][MODULE_CHECK]
> [FIRMWARE_CHECK]
> [KEXEC_KERNEL_CHECK] [KEXEC_INITRAMFS_CHECK]
> - [KEXEC_CMDLINE] [KEY_CHECK]
> + [KEXEC_CMDLINE] [KEY_CHECK] [CRITICAL_DATA]
> mask:= [[^]MAY_READ] [[^]MAY_WRITE] [[^]MAY_APPEND]
> [[^]MAY_EXEC]
> fsmagic:= hex value
> @@ -125,3 +125,7 @@ Description:
> keys added to .builtin_trusted_keys or .ima keyring:
>
> measure func=KEY_CHECK keyrings=.builtin_trusted_keys|.ima
> +
> + Example of measure rule using CRITICAL_DATA to measure critical data
> +
> + measure func=CRITICAL_DATA data_sources=selinux|apparmor|dm-crypt
This example uses "data_sources" without first defining it in the
"option:" section. Defining two new options is an indication that this
patch should be split up. One which defines the "CRITICAL_DATA" and
another one which defines the new key value pair. The term
"data_sources" is pretty generic. Perhaps constrain it a bit by re-
naming it "critical_data=". Or was such using a generic name
intentional?
Normally "CRITICAL_DATA" would be defined with the critical data hook,
but that seems to be defined in patch 3/3 "IMA: define IMA hook to
measure critical data from kernel components".
> diff --git a/security/integrity/ima/ima.h b/security/integrity/ima/ima.h
> index 8875085db689..0f4209a92bfb 100644
> --- a/security/integrity/ima/ima.h
> +++ b/security/integrity/ima/ima.h
> @@ -200,6 +200,7 @@ static inline unsigned int ima_hash_key(u8 *digest)
> hook(POLICY_CHECK, policy) \
> hook(KEXEC_CMDLINE, kexec_cmdline) \
> hook(KEY_CHECK, key) \
> + hook(CRITICAL_DATA, critical_data) \
> hook(MAX_CHECK, none)
>
> #define __ima_hook_enumify(ENUM, str) ENUM,
> diff --git a/security/integrity/ima/ima_api.c b/security/integrity/ima/ima_api.c
> index af218babd198..9917e1730cb6 100644
> --- a/security/integrity/ima/ima_api.c
> +++ b/security/integrity/ima/ima_api.c
> @@ -176,7 +176,7 @@ void ima_add_violation(struct file *file, const unsigned char *filename,
> * subj=, obj=, type=, func=, mask=, fsmagic=
> * subj,obj, and type: are LSM specific.
> * func: FILE_CHECK | BPRM_CHECK | CREDS_CHECK | MMAP_CHECK | MODULE_CHECK
> - * | KEXEC_CMDLINE | KEY_CHECK
> + * | KEXEC_CMDLINE | KEY_CHECK | CRITICAL_DATA
> * mask: contains the permission mask
> * fsmagic: hex value
> *
> diff --git a/security/integrity/ima/ima_policy.c b/security/integrity/ima/ima_policy.c
> index 8866e84d0062..7b649095ac7a 100644
> --- a/security/integrity/ima/ima_policy.c
> +++ b/security/integrity/ima/ima_policy.c
> @@ -33,6 +33,7 @@
> #define IMA_PCR 0x0100
> #define IMA_FSNAME 0x0200
> #define IMA_KEYRINGS 0x0400
> +#define IMA_DATA_SOURCES 0x0800
>
> #define UNKNOWN 0
> #define MEASURE 0x0001 /* same as IMA_MEASURE */
> @@ -84,6 +85,7 @@ struct ima_rule_entry {
> } lsm[MAX_LSM_RULES];
> char *fsname;
> struct ima_rule_opt_list *keyrings; /* Measure keys added to these keyrings */
> + struct ima_rule_opt_list *data_sources; /* Measure data from these sources */
> struct ima_template_desc *template;
> };
>
> @@ -508,14 +510,23 @@ static bool ima_match_rules(struct ima_rule_entry *rule, struct inode *inode,
> {
> int i;
>
> - if (func == KEY_CHECK) {
> - return (rule->flags & IMA_FUNC) && (rule->func == func) &&
> - ima_match_rule_data(rule, rule->keyrings, func_data,
> - true, cred);
> - }
> if ((rule->flags & IMA_FUNC) &&
> (rule->func != func && func != POST_SETATTR))
> return false;
> +
> + switch (func) {
> + case KEY_CHECK:
> + return ((rule->func == func) &&
> + ima_match_rule_data(rule, rule->keyrings,
> + func_data, true, cred));
> + case CRITICAL_DATA:
> + return ((rule->func == func) &&
> + ima_match_rule_data(rule, rule->data_sources,
> + func_data, false, cred));
> + default:
> + break;
> + }
> +
> if ((rule->flags & IMA_MASK) &&
> (rule->mask != mask && func != POST_SETATTR))
> return false;
> @@ -911,7 +922,7 @@ enum {
> Opt_uid_lt, Opt_euid_lt, Opt_fowner_lt,
> Opt_appraise_type, Opt_appraise_flag,
> Opt_permit_directio, Opt_pcr, Opt_template, Opt_keyrings,
> - Opt_err
> + Opt_data_sources, Opt_err
> };
>
> static const match_table_t policy_tokens = {
> @@ -948,6 +959,7 @@ static const match_table_t policy_tokens = {
> {Opt_pcr, "pcr=%s"},
> {Opt_template, "template=%s"},
> {Opt_keyrings, "keyrings=%s"},
> + {Opt_data_sources, "data_sources=%s"},
> {Opt_err, NULL}
> };
>
> @@ -1110,6 +1122,19 @@ static bool ima_validate_rule(struct ima_rule_entry *entry)
> if (ima_rule_contains_lsm_cond(entry))
> return false;
>
> + break;
> + case CRITICAL_DATA:
> + if (entry->action & ~(MEASURE | DONT_MEASURE))
> + return false;
> +
> + if (!(entry->flags & IMA_DATA_SOURCES) ||
> + (entry->flags & ~(IMA_FUNC | IMA_UID | IMA_PCR |
> + IMA_DATA_SOURCES)))
> + return false;
Requiring IMA_FUNC and IMA_DATA_SOURCES makes sense, but why are
IMA_UID and IMA_PCR required?
> +
> + if (ima_rule_contains_lsm_cond(entry))
> + return false;
> +
> break;
> default:
> return false;
> @@ -1242,6 +1267,8 @@ static int ima_parse_rule(char *rule, struct ima_rule_entry *entry)
> else if (IS_ENABLED(CONFIG_IMA_MEASURE_ASYMMETRIC_KEYS) &&
> strcmp(args[0].from, "KEY_CHECK") == 0)
> entry->func = KEY_CHECK;
> + else if (strcmp(args[0].from, "CRITICAL_DATA") == 0)
> + entry->func = CRITICAL_DATA;
> else
> result = -EINVAL;
> if (!result)
> @@ -1312,6 +1339,23 @@ static int ima_parse_rule(char *rule, struct ima_rule_entry *entry)
>
> entry->flags |= IMA_KEYRINGS;
> break;
> + case Opt_data_sources:
> + ima_log_string(ab, "data_sources", args[0].from);
> +
> + if (entry->data_sources) {
> + result = -EINVAL;
> + break;
> + }
> +
> + entry->data_sources = ima_alloc_rule_opt_list(args);
> + if (IS_ERR(entry->data_sources)) {
> + result = PTR_ERR(entry->data_sources);
> + entry->data_sources = NULL;
> + break;
> + }
> +
"keyrings=" isn't bounded because keyrings can be created by userspace.
Perhaps keyring names has a minimum/maximum length. IMA isn't
measuring userspace construsts. Shouldn't the list of critical data
being measured be bounded and verified?
Mimi
> + entry->flags |= IMA_DATA_SOURCES;
> + break;
> case Opt_fsuuid:
> ima_log_string(ab, "fsuuid", args[0].from);
>
> @@ -1692,6 +1736,12 @@ int ima_policy_show(struct seq_file *m, void *v)
> seq_puts(m, " ");
> }
>
> + if (entry->flags & IMA_DATA_SOURCES) {
> + seq_puts(m, "data_sources=");
> + ima_show_rule_opt_list(m, entry->data_sources);
> + seq_puts(m, " ");
> + }
> +
> if (entry->flags & IMA_PCR) {
> snprintf(tbuf, sizeof(tbuf), "%d", entry->pcr);
> seq_printf(m, pt(Opt_pcr), tbuf);
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