This patch defines a new IMA policy rule option "appraise_hash=",
that restricts the hash algorithms accepted for the extended attribute
security.ima when appraising.
This patch is *not* self-contained, as it plugs in the support for
parsing the parameter and showing it to the user, but it doesn't enforce
the hashes yet, this will come in a subsequent patch.
Here is an example of a valid rule that enforces the use of sha256 or
sha512 when appraising iptables binaries:
appraise func=BPRM_CHECK obj_type=iptables_exec_t appraise_type=imasig appraise_hash=sha256,sha512
This do not apply only to IMA in hash mode, it also works with digital
signatures, in which case it requires the hash (which was then signed
by a trusted private key) to have been generated with one of the
whitelisted algorithms.
Signed-off-by: Simon Thoby <simon.thoby@xxxxxxxxxx>
---
Documentation/ABI/testing/ima_policy | 6 +-
security/integrity/ima/ima.h | 2 +-
security/integrity/ima/ima_policy.c | 82 +++++++++++++++++++++++++++-
3 files changed, 85 insertions(+), 5 deletions(-)
diff --git a/Documentation/ABI/testing/ima_policy b/Documentation/ABI/testing/ima_policy
index 070779e8d836..365e4c91719e 100644
--- a/Documentation/ABI/testing/ima_policy
+++ b/Documentation/ABI/testing/ima_policy
@@ -27,7 +27,7 @@ Description:
lsm: [[subj_user=] [subj_role=] [subj_type=]
[obj_user=] [obj_role=] [obj_type=]]
option: [[appraise_type=]] [template=] [permit_directio]
- [appraise_flag=] [keyrings=]
+ [appraise_flag=] [keyrings=] [appraise_hash=]
base:
func:= [BPRM_CHECK][MMAP_CHECK][CREDS_CHECK][FILE_CHECK][MODULE_CHECK]
[FIRMWARE_CHECK]
@@ -55,6 +55,10 @@ Description:
label:= [selinux]|[kernel_info]|[data_label]
data_label:= a unique string used for grouping and limiting critical data.
For example, "selinux" to measure critical data for SELinux.
+ appraise_hash:= comma-separated list of hash algorithms
+ For example, "sha256,sha512" to only accept to appraise
+ files where the security.ima xattr was hashed with one
+ of these two algorithms.
default policy:
# PROC_SUPER_MAGIC
diff --git a/security/integrity/ima/ima.h b/security/integrity/ima/ima.h
index f0e448ed1f9f..049748e3fe9b 100644
--- a/security/integrity/ima/ima.h
+++ b/security/integrity/ima/ima.h
@@ -47,7 +47,7 @@ enum tpm_pcrs { TPM_PCR0 = 0, TPM_PCR8 = 8, TPM_PCR10 = 10 };
extern int ima_policy_flag;
/* set during initialization */
-extern int ima_hash_algo;
+extern int ima_hash_algo __ro_after_init;
extern int ima_sha1_idx __ro_after_init;
extern int ima_hash_algo_idx __ro_after_init;
extern int ima_extra_slots __ro_after_init;
diff --git a/security/integrity/ima/ima_policy.c b/security/integrity/ima/ima_policy.c
index fd5d46e511f1..1b6c00baa397 100644
--- a/security/integrity/ima/ima_policy.c
+++ b/security/integrity/ima/ima_policy.c
@@ -35,6 +35,7 @@
#define IMA_FSNAME 0x0200
#define IMA_KEYRINGS 0x0400
#define IMA_LABEL 0x0800
+#define IMA_VALIDATE_HASH 0x1000
#define UNKNOWN 0
#define MEASURE 0x0001 /* same as IMA_MEASURE */
@@ -79,6 +80,7 @@ struct ima_rule_entry {
bool (*uid_op)(kuid_t, kuid_t); /* Handlers for operators */
bool (*fowner_op)(kuid_t, kuid_t); /* uid_eq(), uid_gt(), uid_lt() */
int pcr;
+ unsigned int allowed_hashes;
struct {
void *rule; /* LSM file metadata specific */
char *args_p; /* audit value */
@@ -90,6 +92,15 @@ struct ima_rule_entry {
struct ima_template_desc *template;
};
+
+/**
+ * sanity check in case the kernels gains more hash algorithms that can
+ * fit in un unsigned int
+ */
+static_assert(
+ 8 * sizeof(unsigned int) >= HASH_ALGO__LAST,
+ "The bitfields allowed_hashes in ruleset are too small to contain all the supported hash algorithms, consider changing its type");
+
/*
* Without LSM specific knowledge, the default policy can only be
* written in terms of .action, .func, .mask, .fsmagic, .uid, and .fowner
@@ -948,7 +959,7 @@ 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_label, Opt_err
+ Opt_label, Opt_appraise_hash, Opt_err
};
static const match_table_t policy_tokens = {
@@ -986,6 +997,7 @@ static const match_table_t policy_tokens = {
{Opt_template, "template=%s"},
{Opt_keyrings, "keyrings=%s"},
{Opt_label, "label=%s"},
+ {Opt_appraise_hash, "appraise_hash=%s"},
{Opt_err, NULL}
};
@@ -1111,7 +1123,7 @@ static bool ima_validate_rule(struct ima_rule_entry *entry)
IMA_UID | IMA_FOWNER | IMA_FSUUID |
IMA_INMASK | IMA_EUID | IMA_PCR |
IMA_FSNAME | IMA_DIGSIG_REQUIRED |
- IMA_PERMIT_DIRECTIO))
+ IMA_PERMIT_DIRECTIO | IMA_VALIDATE_HASH))
return false;
break;
@@ -1123,7 +1135,7 @@ static bool ima_validate_rule(struct ima_rule_entry *entry)
IMA_INMASK | IMA_EUID | IMA_PCR |
IMA_FSNAME | IMA_DIGSIG_REQUIRED |
IMA_PERMIT_DIRECTIO | IMA_MODSIG_ALLOWED |
- IMA_CHECK_BLACKLIST))
+ IMA_CHECK_BLACKLIST | IMA_VALIDATE_HASH))
return false;
break;
@@ -1173,6 +1185,27 @@ static bool ima_validate_rule(struct ima_rule_entry *entry)
return true;
}
+static unsigned int ima_parse_appraise_hash(char *arg)
+{
+ unsigned int res = 0;
+ char *token;
+
+ while ((token = strsep(&arg, ",")) != NULL) {
+ int idx = match_string(hash_algo_name, HASH_ALGO__LAST, token);
+
+ if (idx < 0) {
+ pr_err("unknown hash algorithm \"%s\", ignoring",
+ token);
+ continue;
+ }
+
+ /* Add the hash algorithm to the 'allowed' bitfield */
+ res |= (1U << idx);
+ }
+
+ return res;
+}
+
static int ima_parse_rule(char *rule, struct ima_rule_entry *entry)
{
struct audit_buffer *ab;
@@ -1190,6 +1223,7 @@ static int ima_parse_rule(char *rule, struct ima_rule_entry *entry)
entry->uid_op = &uid_eq;
entry->fowner_op = &uid_eq;
entry->action = UNKNOWN;
+ entry->allowed_hashes = 0;
while ((p = strsep(&rule, " \t")) != NULL) {
substring_t args[MAX_OPT_ARGS];
int token;
@@ -1542,6 +1576,23 @@ static int ima_parse_rule(char *rule, struct ima_rule_entry *entry)
&(template_desc->fields),
&(template_desc->num_fields));
entry->template = template_desc;
+ break;
+ case Opt_appraise_hash:
+ ima_log_string(ab, "appraise_hash", args[0].from);
+
+ if (entry->allowed_hashes) {
+ result = -EINVAL;
+ break;
+ }
+
+ entry->allowed_hashes = ima_parse_appraise_hash(args[0].from);
+ if (!entry->allowed_hashes) {
+ result = -EINVAL;
+ break;
+ }
+
+ entry->flags |= IMA_VALIDATE_HASH;
+
break;
case Opt_err:
ima_log_string(ab, "UNKNOWN", p);
@@ -1700,6 +1751,25 @@ static void ima_show_rule_opt_list(struct seq_file *m,
seq_printf(m, "%s%s", i ? "|" : "", opt_list->items[i]);
}
+static void ima_policy_show_appraise_hash(struct seq_file *m,
+ unsigned int allowed_hashes)
+{
+ int idx;
+ bool first = true;
+
+ for (idx = 0; idx < HASH_ALGO__LAST; idx++) {
+ if (!(allowed_hashes & (1U << idx)))
+ continue;
+
+ if (!first)
+ seq_puts(m, ",");
+ first = false;
+
+ seq_puts(m, hash_algo_name[idx]);
+ }
+
+}
+
int ima_policy_show(struct seq_file *m, void *v)
{
struct ima_rule_entry *entry = v;
@@ -1811,6 +1881,12 @@ int ima_policy_show(struct seq_file *m, void *v)
seq_puts(m, " ");
}
+ if (entry->flags & IMA_VALIDATE_HASH) {
+ seq_puts(m, "appraise_hash=");
+ ima_policy_show_appraise_hash(m, entry->allowed_hashes);
+ seq_puts(m, " ");
+ }
+
for (i = 0; i < MAX_LSM_RULES; i++) {
if (entry->lsm[i].rule) {
switch (i) {
--
2.31.1
