linux-kernel - [PATCH v10 12/25] security: Introduce file_post

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Message-Id: <20240215103113.2369171-13-roberto.sassu@huaweicloud.com>
Date: Thu, 15 Feb 2024 11:31:00 +0100
From: Roberto Sassu <roberto.sassu@...weicloud.com>
To: viro@...iv.linux.org.uk,
	brauner@...nel.org,
	jack@...e.cz,
	chuck.lever@...cle.com,
	jlayton@...nel.org,
	neilb@...e.de,
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	Dai.Ngo@...cle.com,
	tom@...pey.com,
	paul@...l-moore.com,
	jmorris@...ei.org,
	serge@...lyn.com,
	zohar@...ux.ibm.com,
	dmitry.kasatkin@...il.com,
	eric.snowberg@...cle.com,
	dhowells@...hat.com,
	jarkko@...nel.org,
	stephen.smalley.work@...il.com,
	omosnace@...hat.com,
	casey@...aufler-ca.com,
	shuah@...nel.org,
	mic@...ikod.net
Cc: linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org,
	linux-nfs@...r.kernel.org,
	linux-security-module@...r.kernel.org,
	linux-integrity@...r.kernel.org,
	keyrings@...r.kernel.org,
	selinux@...r.kernel.org,
	linux-kselftest@...r.kernel.org,
	Roberto Sassu <roberto.sassu@...wei.com>,
	Stefan Berger <stefanb@...ux.ibm.com>
Subject: [PATCH v10 12/25] security: Introduce file_post_open hook

From: Roberto Sassu <roberto.sassu@...wei.com>

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@...wei.com>
Reviewed-by: Stefan Berger <stefanb@...ux.ibm.com>
Acked-by: Casey Schaufler <casey@...aufler-ca.com>
Reviewed-by: Mimi Zohar <zohar@...ux.ibm.com>
Acked-by: Paul Moore <paul@...l-moore.com>
Acked-by: Christian Brauner <brauner@...nel.org>
---
 fs/namei.c                    |  2 ++
 fs/nfsd/vfs.c                 |  6 ++++++
 include/linux/lsm_hook_defs.h |  1 +
 include/linux/security.h      |  6 ++++++
 security/security.c           | 17 +++++++++++++++++
 5 files changed, 32 insertions(+)

diff --git a/fs/namei.c b/fs/namei.c
index 4e0de939fea1..ef867f1d6704 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -3639,6 +3639,8 @@ static int do_open(struct nameidata *nd,
 	error = may_open(idmap, &nd->path, acc_mode, open_flag);
 	if (!error && !(file->f_mode & FMODE_OPENED))
 		error = vfs_open(&nd->path, file);
+	if (!error)
+		error = security_file_post_open(file, op->acc_mode);
 	if (!error)
 		error = ima_file_check(file, op->acc_mode);
 	if (!error && do_truncate)
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);
diff --git a/include/linux/lsm_hook_defs.h b/include/linux/lsm_hook_defs.h
index f849f7d5bb53..3c84942d2818 100644
--- a/include/linux/lsm_hook_defs.h
+++ b/include/linux/lsm_hook_defs.h
@@ -191,6 +191,7 @@ LSM_HOOK(int, 0, file_send_sigiotask, struct task_struct *tsk,
 	 struct fown_struct *fown, int sig)
 LSM_HOOK(int, 0, file_receive, struct file *file)
 LSM_HOOK(int, 0, file_open, struct file *file)
+LSM_HOOK(int, 0, file_post_open, struct file *file, int mask)
 LSM_HOOK(int, 0, file_truncate, struct file *file)
 LSM_HOOK(int, 0, task_alloc, struct task_struct *task,
 	 unsigned long clone_flags)
diff --git a/include/linux/security.h b/include/linux/security.h
index 84ae03690340..97f2212c13b6 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -411,6 +411,7 @@ int security_file_send_sigiotask(struct task_struct *tsk,
 				 struct fown_struct *fown, int sig);
 int security_file_receive(struct file *file);
 int security_file_open(struct file *file);
+int security_file_post_open(struct file *file, int mask);
 int security_file_truncate(struct file *file);
 int security_task_alloc(struct task_struct *task, unsigned long clone_flags);
 void security_task_free(struct task_struct *task);
@@ -1074,6 +1075,11 @@ static inline int security_file_open(struct file *file)
 	return 0;
 }
 
+static inline int security_file_post_open(struct file *file, int mask)
+{
+	return 0;
+}
+
 static inline int security_file_truncate(struct file *file)
 {
 	return 0;
diff --git a/security/security.c b/security/security.c
index 0f0f2c11ef73..5b442032c273 100644
--- a/security/security.c
+++ b/security/security.c
@@ -2967,6 +2967,23 @@ int security_file_open(struct file *file)
 	return fsnotify_open_perm(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
-- 
2.34.1