ima: handle idmapped mounts

IMA does sometimes access the inode's i_uid and compares it against the
rules' fowner. Enable IMA to handle idmapped mounts by passing down the
mount's user namespace. We simply make use of the helpers we introduced
before. If the initial user namespace is passed nothing changes so
non-idmapped mounts will see identical behavior as before.

Link: https://lore.kernel.org/r/20210121131959.646623-27-christian.brauner@ubuntu.com
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

1 files changed, 12 insertions, 8 deletions

diff --git a/security/integrity/ima/ima_policy.c b/security/integrity/ima/ima_policy.c
index 823a0c1379cb..e14426c24a19 100644
--- a/security/integrity/ima/ima_policy.c
+++ b/security/integrity/ima/ima_policy.c
@@ -488,6 +488,7 @@ static bool ima_match_keyring(struct ima_rule_entry *rule,
 /**
  * ima_match_rules - determine whether an inode matches the policy rule.
  * @rule: a pointer to a rule
+ * @mnt_userns:	user namespace of the mount the inode was found from
  * @inode: a pointer to an inode
  * @cred: a pointer to a credentials structure for user validation
  * @secid: the secid of the task to be validated
@@ -497,9 +498,10 @@ static bool ima_match_keyring(struct ima_rule_entry *rule,
  *
  * Returns true on rule match, false on failure.
  */
-static bool ima_match_rules(struct ima_rule_entry *rule, struct inode *inode,
-			    const struct cred *cred, u32 secid,
-			    enum ima_hooks func, int mask,
+static bool ima_match_rules(struct ima_rule_entry *rule,
+			    struct user_namespace *mnt_userns,
+			    struct inode *inode, const struct cred *cred,
+			    u32 secid, enum ima_hooks func, int mask,
 			    const char *keyring)
 {
 	int i;
@@ -539,7 +541,7 @@ static bool ima_match_rules(struct ima_rule_entry *rule, struct inode *inode,
 	}
 
 	if ((rule->flags & IMA_FOWNER) &&
-	    !rule->fowner_op(inode->i_uid, rule->fowner))
+	    !rule->fowner_op(i_uid_into_mnt(mnt_userns, inode), rule->fowner))
 		return false;
 	for (i = 0; i < MAX_LSM_RULES; i++) {
 		int rc = 0;
@@ -602,6 +604,7 @@ static int get_subaction(struct ima_rule_entry *rule, enum ima_hooks func)
 
 /**
  * ima_match_policy - decision based on LSM and other conditions
+ * @mnt_userns:	user namespace of the mount the inode was found from
  * @inode: pointer to an inode for which the policy decision is being made
  * @cred: pointer to a credentials structure for which the policy decision is
  *        being made
@@ -620,8 +623,9 @@ static int get_subaction(struct ima_rule_entry *rule, enum ima_hooks func)
  * list when walking it.  Reads are many orders of magnitude more numerous
  * than writes so ima_match_policy() is classical RCU candidate.
  */
-int ima_match_policy(struct inode *inode, const struct cred *cred, u32 secid,
-		     enum ima_hooks func, int mask, int flags, int *pcr,
+int ima_match_policy(struct user_namespace *mnt_userns, struct inode *inode,
+		     const struct cred *cred, u32 secid, enum ima_hooks func,
+		     int mask, int flags, int *pcr,
 		     struct ima_template_desc **template_desc,
 		     const char *keyring)
 {
@@ -637,8 +641,8 @@ int ima_match_policy(struct inode *inode, const struct cred *cred, u32 secid,
 		if (!(entry->action & actmask))
 			continue;
 
-		if (!ima_match_rules(entry, inode, cred, secid, func, mask,
-				     keyring))
+		if (!ima_match_rules(entry, mnt_userns, inode, cred, secid,
+				     func, mask, keyring))
 			continue;
 
 		action |= entry->flags & IMA_ACTION_FLAGS;