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 <roberto.sassu@huawei.com>
Reviewed-by: Stefan Berger <stefanb@linux.ibm.com>
Acked-by: Casey Schaufler <casey@schaufler-ca.com>
Reviewed-by: Mimi Zohar <zohar@linux.ibm.com>
Acked-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Paul Moore <paul@paul-moore.com>

1 files changed, 6 insertions, 0 deletions

diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c
index b7c7a9273ea0..e44d8239545b 100644
--- a/fs/nfsd/vfs.c
+++ b/fs/nfsd/vfs.c
@@ -877,6 +877,12 @@ __nfsd_open(struct svc_rqst *rqstp, struct svc_fh *fhp, umode_t type,
 		goto out;
 	}
 
+	host_err = security_file_post_open(file, may_flags);
+	if (host_err) {
+		fput(file);
+		goto out;
+	}
+
 	host_err = ima_file_check(file, may_flags);
 	if (host_err) {
 		fput(file);