linux-kernel - [PATCH v2 14/25] security: Introduce file_post

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Date:   Thu, 31 Aug 2023 12:41:25 +0200
From:   Roberto Sassu <roberto.sassu@...weicloud.com>
To:     viro@...iv.linux.org.uk, brauner@...nel.org,
        chuck.lever@...cle.com, jlayton@...nel.org, neilb@...e.de,
        kolga@...app.com, Dai.Ngo@...cle.com, tom@...pey.com,
        zohar@...ux.ibm.com, dmitry.kasatkin@...il.com,
        paul@...l-moore.com, jmorris@...ei.org, serge@...lyn.com,
        dhowells@...hat.com, jarkko@...nel.org,
        stephen.smalley.work@...il.com, eparis@...isplace.org,
        casey@...aufler-ca.com
Cc:     linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-nfs@...r.kernel.org, linux-integrity@...r.kernel.org,
        linux-security-module@...r.kernel.org, keyrings@...r.kernel.org,
        selinux@...r.kernel.org, Roberto Sassu <roberto.sassu@...wei.com>,
        Stefan Berger <stefanb@...ux.ibm.com>
Subject: [PATCH v2 14/25] 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.

Signed-off-by: Roberto Sassu <roberto.sassu@...wei.com>
Reviewed-by: Stefan Berger <stefanb@...ux.ibm.com>
---
 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 1f5ec71360de..7dc4626859f0 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -3634,6 +3634,8 @@ 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 8a2321d19194..3450bb1c8a18 100644
--- a/fs/nfsd/vfs.c
+++ b/fs/nfsd/vfs.c
@@ -862,6 +862,12 @@ __nfsd_open(struct svc_rqst *rqstp, struct svc_fh *fhp, umode_t type,
 		goto out_nfserr;
 	}
 
+	host_err = security_file_post_open(file, may_flags);
+	if (host_err) {
+		fput(file);
+		goto out_nfserr;
+	}
+
 	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 1153e7163b8b..60ed33f0c80d 100644
--- a/include/linux/lsm_hook_defs.h
+++ b/include/linux/lsm_hook_defs.h
@@ -188,6 +188,7 @@ 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 665bba3e0081..a0f16511c059 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -403,6 +403,7 @@ 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);
@@ -1044,6 +1045,11 @@ 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 3947159ba5e9..3e0078b51e46 100644
--- a/security/security.c
+++ b/security/security.c
@@ -2856,6 +2856,23 @@ int security_file_open(struct file *file)
 	return fsnotify_perm(file, MAY_OPEN);
 }
 
+/**
+ * security_file_post_open() - Recheck access to a file after it has been opened
+ * @file: the file
+ * @mask: access mask
+ *
+ * Recheck access with mask after the file has been opened. 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