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Subject[PATCH] IMA: pre-allocate keyrings string
Date
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
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