security: Introduce file_post_open hook

In preparation to move IMA and EVM to the LSM infrastructure, introduce the
file_post_open hook. Also, export security_file_post_open() for NFS.

Based on policy, IMA calculates the digest of the file content and
extends the TPM with the digest, verifies the file's integrity based on
the digest, and/or includes the file digest in the audit log.

LSMs could similarly take action depending on the file content and the
access mask requested with open().

The new hook returns a value and can cause the open to be aborted.

Signed-off-by: Roberto Sassu <[email protected]>
Reviewed-by: Stefan Berger <[email protected]>
Acked-by: Casey Schaufler <[email protected]>
Reviewed-by: Mimi Zohar <[email protected]>
Acked-by: Christian Brauner <[email protected]>
Signed-off-by: Paul Moore <[email protected]>

1 files changed, 17 insertions, 0 deletions

diff --git a/security/security.c b/security/security.c
index d77fdd3ca1bc..207405a84902 100644
--- a/security/security.c
+++ b/security/security.c
@@ -2967,6 +2967,23 @@ int security_file_open(struct file *file)
 }
 
 /**
+ * security_file_post_open() - Evaluate a file after it has been opened
+ * @file: the file
+ * @mask: access mask
+ *
+ * Evaluate an opened file and the access mask requested with open(). The hook
+ * is useful for LSMs that require the file content to be available in order to
+ * make decisions.
+ *
+ * Return: Returns 0 if permission is granted.
+ */
+int security_file_post_open(struct file *file, int mask)
+{
+	return call_int_hook(file_post_open, 0, file, mask);
+}
+EXPORT_SYMBOL_GPL(security_file_post_open);
+
+/**
  * security_file_truncate() - Check if truncating a file is allowed
  * @file: file
  *