[PATCH] IMA: pre-allocate keyrings string

[Lakshmi Ramasubramanian <nramas@linux.microsoft.com>]

ima_match_keyring() is called while holding rcu read lock.
Since this function executes in atmomic 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 check
the given keyring in ima_match_keyring().

Signed-off-by: Lakshmi Ramasubramanian <nramas@linux.microsoft.com>
Fixes: e9085e0ad38a ("IMA: Add support to limit measuring keys")
---
 security/integrity/ima/ima_policy.c | 20 +++++++++++++-------
 1 file changed, 13 insertions(+), 7 deletions(-)

diff --git a/security/integrity/ima/ima_policy.c b/security/integrity/ima/ima_policy.c
index 9963863d6c92..0bb4376ddba7 100644
--- a/security/integrity/ima/ima_policy.c
+++ b/security/integrity/ima/ima_policy.c
@@ -207,6 +207,7 @@ static LIST_HEAD(ima_default_rules);
 static LIST_HEAD(ima_policy_rules);
 static LIST_HEAD(ima_temp_rules);
 static struct list_head *ima_rules;
+static char *ima_keyrings;
 
 static int ima_policy __initdata;
 
@@ -369,7 +370,7 @@ 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))
@@ -381,15 +382,13 @@ 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;
@@ -397,8 +396,6 @@ static bool ima_match_keyring(struct ima_rule_entry *rule,
 		}
 	}
 
-	kfree(keyrings);
-
 	return matched;
 }
 
@@ -1120,8 +1117,17 @@ static int ima_parse_rule(char *rule, struct ima_rule_entry *entry)
 				result = -EINVAL;
 				break;
 			}
+
+			ima_keyrings = kstrdup(args[0].from, GFP_KERNEL);
+			if (!ima_keyrings) {
+				result = -ENOMEM;
+				break;
+			}
+
 			entry->keyrings = kstrdup(args[0].from, GFP_KERNEL);
 			if (!entry->keyrings) {
+				kfree(ima_keyrings);
+				ima_keyrings = NULL;
 				result = -ENOMEM;
 				break;
 			}
-- 
2.17.1