lsm: add the inode_free_security_rcu() LSM implementation hook

The LSM framework has an existing inode_free_security() hook which
is used by LSMs that manage state associated with an inode, but
due to the use of RCU to protect the inode, special care must be
taken to ensure that the LSMs do not fully release the inode state
until it is safe from a RCU perspective.

This patch implements a new inode_free_security_rcu() implementation
hook which is called when it is safe to free the LSM's internal inode
state.  Unfortunately, this new hook does not have access to the inode
itself as it may already be released, so the existing
inode_free_security() hook is retained for those LSMs which require
access to the inode.

Cc: stable@vger.kernel.org
Reported-by: syzbot+5446fbf332b0602ede0b@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/r/00000000000076ba3b0617f65cc8@google.com
Signed-off-by: Paul Moore <paul@paul-moore.com>

1 files changed, 8 insertions, 12 deletions

diff --git a/security/integrity/ima/ima_iint.c b/security/integrity/ima/ima_iint.c
index e23412a2c56b..00b249101f98 100644
--- a/security/integrity/ima/ima_iint.c
+++ b/security/integrity/ima/ima_iint.c
@@ -109,22 +109,18 @@ struct ima_iint_cache *ima_inode_get(struct inode *inode)
 }
 
 /**
- * ima_inode_free - Called on inode free
- * @inode: Pointer to the inode
+ * ima_inode_free_rcu - Called to free an inode via a RCU callback
+ * @inode_security: The inode->i_security pointer
  *
- * Free the iint associated with an inode.
+ * Free the IMA data associated with an inode.
  */
-void ima_inode_free(struct inode *inode)
+void ima_inode_free_rcu(void *inode_security)
 {
-	struct ima_iint_cache *iint;
-
-	if (!IS_IMA(inode))
-		return;
-
-	iint = ima_iint_find(inode);
-	ima_inode_set_iint(inode, NULL);
+	struct ima_iint_cache **iint_p = inode_security + ima_blob_sizes.lbs_inode;
 
-	ima_iint_free(iint);
+	/* *iint_p should be NULL if !IS_IMA(inode) */
+	if (*iint_p)
+		ima_iint_free(*iint_p);
 }
 
 static void ima_iint_init_once(void *foo)