IMA: pre-allocate buffer to hold keyrings string

ima_match_keyring() is called while holding rcu read lock. Since this
function executes in atomic context, it should not call any function
that can sleep (such as kstrdup()).

This patch pre-allocates a buffer to hold the keyrings string read from
the IMA policy and uses that to match the given keyring.

Signed-off-by: Lakshmi Ramasubramanian <nramas@linux.microsoft.com>
Fixes: e9085e0ad38a ("IMA: Add support to limit measuring keys")
Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>

diff --git a/security/integrity/ima/ima_policy.c b/security/integrity/ima/ima_policy.c
index 638fe7c..b560a3f 100644 (file)
--- a/security/integrity/ima/ima_policy.c
+++ b/security/integrity/ima/ima_policy.c
@@ -208,6 +208,10 @@ static LIST_HEAD(ima_policy_rules);
 static LIST_HEAD(ima_temp_rules);
 static struct list_head *ima_rules;
 
+/* Pre-allocated buffer used for matching keyrings. */
+static char *ima_keyrings;
+static size_t ima_keyrings_len;
+
 static int ima_policy __initdata;
 
 static int __init default_measure_policy_setup(char *str)
@@ -368,7 +372,7 @@ int ima_lsm_policy_change(struct notifier_block *nb, unsigned long event,
 static bool ima_match_keyring(struct ima_rule_entry *rule,
                              const char *keyring, const struct cred *cred)
 {
-       char *keyrings, *next_keyring, *keyrings_ptr;
+       char *next_keyring, *keyrings_ptr;
        bool matched = false;
 
        if ((rule->flags & IMA_UID) && !rule->uid_op(cred->uid, rule->uid))
@@ -380,15 +384,13 @@ static bool ima_match_keyring(struct ima_rule_entry *rule,
        if (!keyring)
                return false;
 
-       keyrings = kstrdup(rule->keyrings, GFP_KERNEL);
-       if (!keyrings)
-               return false;
+       strcpy(ima_keyrings, rule->keyrings);
 
        /*
         * "keyrings=" is specified in the policy in the format below:
         * keyrings=.builtin_trusted_keys|.ima|.evm
         */
-       keyrings_ptr = keyrings;
+       keyrings_ptr = ima_keyrings;
        while ((next_keyring = strsep(&keyrings_ptr, "|")) != NULL) {
                if (!strcmp(next_keyring, keyring)) {
                        matched = true;
@@ -396,8 +398,6 @@ static bool ima_match_keyring(struct ima_rule_entry *rule,
                }
        }
 
-       kfree(keyrings);
-
        return matched;
 }
 
@@ -954,6 +954,7 @@ static int ima_parse_rule(char *rule, struct ima_rule_entry *entry)
        bool uid_token;
        struct ima_template_desc *template_desc;
        int result = 0;
+       size_t keyrings_len;
 
        ab = integrity_audit_log_start(audit_context(), GFP_KERNEL,
                                       AUDIT_INTEGRITY_POLICY_RULE);
@@ -1119,14 +1120,35 @@ static int ima_parse_rule(char *rule, struct ima_rule_entry *entry)
                case Opt_keyrings:
                        ima_log_string(ab, "keyrings", args[0].from);
 
+                       keyrings_len = strlen(args[0].from) + 1;
+
                        if ((entry->keyrings) ||
                            (entry->action != MEASURE) ||
-                           (entry->func != KEY_CHECK)) {
+                           (entry->func != KEY_CHECK) ||
+                           (keyrings_len < 2)) {
                                result = -EINVAL;
                                break;
                        }
+
+                       if (keyrings_len > ima_keyrings_len) {
+                               char *tmpbuf;
+
+                               tmpbuf = krealloc(ima_keyrings, keyrings_len,
+                                                 GFP_KERNEL);
+                               if (!tmpbuf) {
+                                       result = -ENOMEM;
+                                       break;
+                               }
+
+                               ima_keyrings = tmpbuf;
+                               ima_keyrings_len = keyrings_len;
+                       }
+
                        entry->keyrings = kstrdup(args[0].from, GFP_KERNEL);
                        if (!entry->keyrings) {
+                               kfree(ima_keyrings);
+                               ima_keyrings = NULL;
+                               ima_keyrings_len = 0;
                                result = -ENOMEM;
                                break;
                        }