[PATCH v6 1/3] Add a new LSM-supporting anonymous inode interface

[Lokesh Gidra]

From: Daniel Colascione <dancol@xxxxxxxxxx>

This change adds two new functions, anon_inode_getfile_secure and
anon_inode_getfd_secure, that create anonymous-node files with
individual non-S_PRIVATE inodes to which security modules can apply
policy. Existing callers continue using the original singleton-inode
kind of anonymous-inode file. We can transition anonymous inode users
to the new kind of anonymous inode in individual patches for the sake
of bisection and review.

The new functions accept an optional context_inode parameter that
callers can use to provide additional contextual information to
security modules, e.g., indicating that one anonymous struct file is a
logical child of another, allowing a security model to propagate
security information from one to the other.

Signed-off-by: Daniel Colascione <dancol@xxxxxxxxxx>

[Fix comment documenting return values of inode_init_security_anon()]
[Add context_inode description in comments to anon_inode_getfd_secure()
 and anon_inode_getfile_secure()]
[Make _anon_inode_getfile() static]
[Use correct error cast in _anon_inode_getfile()]

Signed-off-by: Lokesh Gidra <lokeshgidra@xxxxxxxxxx>
---
 fs/anon_inodes.c              | 193 ++++++++++++++++++++++++++--------
 include/linux/anon_inodes.h   |  13 +++
 include/linux/lsm_hook_defs.h |   2 +
 include/linux/lsm_hooks.h     |   7 ++
 include/linux/security.h      |   3 +
 security/security.c           |   9 ++
 6 files changed, 186 insertions(+), 41 deletions(-)

diff --git a/fs/anon_inodes.c b/fs/anon_inodes.c
index 89714308c25b..4e09915fe847 100644
--- a/fs/anon_inodes.c
+++ b/fs/anon_inodes.c
@@ -55,61 +55,109 @@ static struct file_system_type anon_inode_fs_type = {
 	.kill_sb	= kill_anon_super,
 };
 
-/**
- * anon_inode_getfile - creates a new file instance by hooking it up to an
- *                      anonymous inode, and a dentry that describe the "class"
- *                      of the file
- *
- * @name:    [in]    name of the "class" of the new file
- * @fops:    [in]    file operations for the new file
- * @priv:    [in]    private data for the new file (will be file's private_data)
- * @flags:   [in]    flags
- *
- * Creates a new file by hooking it on a single inode. This is useful for files
- * that do not need to have a full-fledged inode in order to operate correctly.
- * All the files created with anon_inode_getfile() will share a single inode,
- * hence saving memory and avoiding code duplication for the file/inode/dentry
- * setup.  Returns the newly created file* or an error pointer.
- */
-struct file *anon_inode_getfile(const char *name,
-				const struct file_operations *fops,
-				void *priv, int flags)
+static struct inode *anon_inode_make_secure_inode(
+	const char *name,
+	const struct inode *context_inode)
 {
+	struct inode *inode;
+	const struct qstr qname = QSTR_INIT(name, strlen(name));
+	int error;
+
+	inode = alloc_anon_inode(anon_inode_mnt->mnt_sb);
+	if (IS_ERR(inode))
+		return inode;
+	inode->i_flags &= ~S_PRIVATE;
+	error =	security_inode_init_security_anon(
+		inode, &qname, context_inode);
+	if (error) {
+		iput(inode);
+		return ERR_PTR(error);
+	}
+	return inode;
+}
+
+static struct file *_anon_inode_getfile(const char *name,
+					const struct file_operations *fops,
+					void *priv, int flags,
+					const struct inode *context_inode,
+					bool secure)
+{
+	struct inode *inode;
 	struct file *file;
 
-	if (IS_ERR(anon_inode_inode))
-		return ERR_PTR(-ENODEV);
+	if (secure) {
+		inode =	anon_inode_make_secure_inode(
+			name, context_inode);
+		if (IS_ERR(inode))
+			return ERR_CAST(inode);
+	} else {
+		inode =	anon_inode_inode;
+		if (IS_ERR(inode))
+			return ERR_PTR(-ENODEV);
+		/*
+		 * We know the anon_inode inode count is always
+		 * greater than zero, so ihold() is safe.
+		 */
+		ihold(inode);
+	}
 
-	if (fops->owner && !try_module_get(fops->owner))
-		return ERR_PTR(-ENOENT);
+	if (fops->owner && !try_module_get(fops->owner)) {
+		file = ERR_PTR(-ENOENT);
+		goto err;
+	}
 
-	/*
-	 * We know the anon_inode inode count is always greater than zero,
-	 * so ihold() is safe.
-	 */
-	ihold(anon_inode_inode);
-	file = alloc_file_pseudo(anon_inode_inode, anon_inode_mnt, name,
+	file = alloc_file_pseudo(inode, anon_inode_mnt, name,
 				 flags & (O_ACCMODE | O_NONBLOCK), fops);
 	if (IS_ERR(file))
 		goto err;
 
-	file->f_mapping = anon_inode_inode->i_mapping;
+	file->f_mapping = inode->i_mapping;
 
 	file->private_data = priv;
 
 	return file;
 
 err:
-	iput(anon_inode_inode);
+	iput(inode);
 	module_put(fops->owner);
 	return file;
 }
-EXPORT_SYMBOL_GPL(anon_inode_getfile);
 
 /**
- * anon_inode_getfd - creates a new file instance by hooking it up to an
- *                    anonymous inode, and a dentry that describe the "class"
- *                    of the file
+ * anon_inode_getfile_secure - creates a new file instance by hooking
+ *                             it up to a new anonymous inode and a
+ *                             dentry that describe the "class" of the
+ *                             file.  Make it possible to use security
+ *                             modules to control access to the
+ *                             new file.
+ *
+ * @name:         [in]  name of the "class" of the new file
+ * @fops:         [in]  file operations for the new file
+ * @priv:         [in]  private data for the new file (will be file's private_data)
+ * @flags:        [in]  flags
+ * @context_inode [in]  inode for additional contextual info to security modules
+ *
+ * Creates a new file by hooking it on an unspecified inode. This is
+ * useful for files that do not need to have a full-fledged filesystem
+ * to operate correctly.  All the files created with
+ * anon_inode_getfile_secure() will have distinct inodes, avoiding
+ * code duplication for the file/inode/dentry setup.  Returns the
+ * newly created file* or an error pointer.
+ */
+struct file *anon_inode_getfile_secure(const char *name,
+				       const struct file_operations *fops,
+				       void *priv, int flags,
+				       const struct inode *context_inode)
+{
+	return _anon_inode_getfile(
+		name, fops, priv, flags, context_inode, true);
+}
+EXPORT_SYMBOL_GPL(anon_inode_getfile_secure);
+
+/**
+ * anon_inode_getfile - creates a new file instance by hooking it up to an
+ *                      anonymous inode, and a dentry that describe the "class"
+ *                      of the file
  *
  * @name:    [in]    name of the "class" of the new file
  * @fops:    [in]    file operations for the new file
@@ -118,12 +166,23 @@ EXPORT_SYMBOL_GPL(anon_inode_getfile);
  *
  * Creates a new file by hooking it on a single inode. This is useful for files
  * that do not need to have a full-fledged inode in order to operate correctly.
- * All the files created with anon_inode_getfd() will share a single inode,
+ * All the files created with anon_inode_getfile() will share a single inode,
  * hence saving memory and avoiding code duplication for the file/inode/dentry
- * setup.  Returns new descriptor or an error code.
+ * setup.  Returns the newly created file* or an error pointer.
  */
-int anon_inode_getfd(const char *name, const struct file_operations *fops,
-		     void *priv, int flags)
+struct file *anon_inode_getfile(const char *name,
+				const struct file_operations *fops,
+				void *priv, int flags)
+{
+	return _anon_inode_getfile(name, fops, priv, flags, NULL, false);
+}
+EXPORT_SYMBOL_GPL(anon_inode_getfile);
+
+static int _anon_inode_getfd(const char *name,
+			     const struct file_operations *fops,
+			     void *priv, int flags,
+			     const struct inode *context_inode,
+			     bool secure)
 {
 	int error, fd;
 	struct file *file;
@@ -133,7 +192,8 @@ int anon_inode_getfd(const char *name, const struct file_operations *fops,
 		return error;
 	fd = error;
 
-	file = anon_inode_getfile(name, fops, priv, flags);
+	file = _anon_inode_getfile(name, fops, priv, flags, context_inode,
+				   secure);
 	if (IS_ERR(file)) {
 		error = PTR_ERR(file);
 		goto err_put_unused_fd;
@@ -146,6 +206,58 @@ int anon_inode_getfd(const char *name, const struct file_operations *fops,
 	put_unused_fd(fd);
 	return error;
 }
+
+/**
+ * anon_inode_getfd_secure - creates a new file instance by hooking it
+ *                           up to a new anonymous inode and a dentry
+ *                           that describe the "class" of the file.
+ *                           Make it possible to use security modules
+ *                           to control access to the new file.
+ *
+ * @name:         [in]  name of the "class" of the new file
+ * @fops:         [in]  file operations for the new file
+ * @priv:         [in]  private data for the new file (will be file's private_data)
+ * @flags:        [in]  flags
+ * @context_inode [in]  inode for additional contextual info to security modules
+ *
+ * Creates a new file by hooking it on an unspecified inode. This is
+ * useful for files that do not need to have a full-fledged filesystem
+ * to operate correctly.  All the files created with
+ * anon_inode_getfile_secure() will have distinct inodes, avoiding
+ * code duplication for the file/inode/dentry setup.  Returns a newly
+ * created file descriptor or an error code.
+ */
+int anon_inode_getfd_secure(const char *name, const struct file_operations *fops,
+			    void *priv, int flags,
+			    const struct inode *context_inode)
+{
+	return _anon_inode_getfd(name, fops, priv, flags,
+				 context_inode, true);
+}
+EXPORT_SYMBOL_GPL(anon_inode_getfd_secure);
+
+/**
+ * anon_inode_getfd - creates a new file instance by hooking it up to
+ *                    an anonymous inode and a dentry that describe
+ *                    the "class" of the file
+ *
+ * @name:    [in]    name of the "class" of the new file
+ * @fops:    [in]    file operations for the new file
+ * @priv:    [in]    private data for the new file (will be file's private_data)
+ * @flags:   [in]    flags
+ *
+ * Creates a new file by hooking it on a single inode. This is
+ * useful for files that do not need to have a full-fledged inode in
+ * order to operate correctly.  All the files created with
+ * anon_inode_getfile() will use the same singleton inode, reducing
+ * memory use and avoiding code duplication for the file/inode/dentry
+ * setup.  Returns a newly created file descriptor or an error code.
+ */
+int anon_inode_getfd(const char *name, const struct file_operations *fops,
+		     void *priv, int flags)
+{
+	return _anon_inode_getfd(name, fops, priv, flags, NULL, false);
+}
 EXPORT_SYMBOL_GPL(anon_inode_getfd);
 
 static int __init anon_inode_init(void)
@@ -162,4 +274,3 @@ static int __init anon_inode_init(void)
 }
 
 fs_initcall(anon_inode_init);
-
diff --git a/include/linux/anon_inodes.h b/include/linux/anon_inodes.h
index d0d7d96261ad..67bd85d92dca 100644
--- a/include/linux/anon_inodes.h
+++ b/include/linux/anon_inodes.h
@@ -10,12 +10,25 @@
 #define _LINUX_ANON_INODES_H
 
 struct file_operations;
+struct inode;
+
+struct file *anon_inode_getfile_secure(const char *name,
+				       const struct file_operations *fops,
+				       void *priv, int flags,
+				       const struct inode *context_inode);
 
 struct file *anon_inode_getfile(const char *name,
 				const struct file_operations *fops,
 				void *priv, int flags);
+
+int anon_inode_getfd_secure(const char *name,
+			    const struct file_operations *fops,
+			    void *priv, int flags,
+			    const struct inode *context_inode);
+
 int anon_inode_getfd(const char *name, const struct file_operations *fops,
 		     void *priv, int flags);
 
+
 #endif /* _LINUX_ANON_INODES_H */
 
diff --git a/include/linux/lsm_hook_defs.h b/include/linux/lsm_hook_defs.h
index af998f93d256..613a3d6306c2 100644
--- a/include/linux/lsm_hook_defs.h
+++ b/include/linux/lsm_hook_defs.h
@@ -113,6 +113,8 @@ LSM_HOOK(void, LSM_RET_VOID, inode_free_security, struct inode *inode)
 LSM_HOOK(int, 0, inode_init_security, struct inode *inode,
 	 struct inode *dir, const struct qstr *qstr, const char **name,
 	 void **value, size_t *len)
+LSM_HOOK(int, 0, inode_init_security_anon, struct inode *inode,
+	 const struct qstr *name, const struct inode *context_inode)
 LSM_HOOK(int, 0, inode_create, struct inode *dir, struct dentry *dentry,
 	 umode_t mode)
 LSM_HOOK(int, 0, inode_link, struct dentry *old_dentry, struct inode *dir,
diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
index 95b7c1d32062..22847380c26c 100644
--- a/include/linux/lsm_hooks.h
+++ b/include/linux/lsm_hooks.h
@@ -233,6 +233,13 @@
  *	Returns 0 if @name and @value have been successfully set,
  *	-EOPNOTSUPP if no security attribute is needed, or
  *	-ENOMEM on memory allocation failure.
+ * @inode_init_security_anon:
+ *      Set up a secure anonymous inode.
+ *      @inode contains the inode structure
+ *      @name name of the anonymous inode class
+ *      @context_inode optional related inode
+ *	Returns 0 on success, -EACCESS if the security module denies the
+ *	creation of this inode, or another -errno upon other errors.
  * @inode_create:
  *	Check permission to create a regular file.
  *	@dir contains inode structure of the parent of the new file.
diff --git a/include/linux/security.h b/include/linux/security.h
index 0a0a03b36a3b..95c133a8f8bb 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -322,6 +322,9 @@ void security_inode_free(struct inode *inode);
 int security_inode_init_security(struct inode *inode, struct inode *dir,
 				 const struct qstr *qstr,
 				 initxattrs initxattrs, void *fs_data);
+int security_inode_init_security_anon(struct inode *inode,
+				      const struct qstr *name,
+				      const struct inode *context_inode);
 int security_old_inode_init_security(struct inode *inode, struct inode *dir,
 				     const struct qstr *qstr, const char **name,
 				     void **value, size_t *len);
diff --git a/security/security.c b/security/security.c
index 70a7ad357bc6..149b3f024e2d 100644
--- a/security/security.c
+++ b/security/security.c
@@ -1057,6 +1057,15 @@ int security_inode_init_security(struct inode *inode, struct inode *dir,
 }
 EXPORT_SYMBOL(security_inode_init_security);
 
+int
+security_inode_init_security_anon(struct inode *inode,
+				  const struct qstr *name,
+				  const struct inode *context_inode)
+{
+	return call_int_hook(inode_init_security_anon, 0, inode, name,
+			     context_inode);
+}
+
 int security_old_inode_init_security(struct inode *inode, struct inode *dir,
 				     const struct qstr *qstr, const char **name,
 				     void **value, size_t *len)
-- 
2.28.0.236.gb10cc79966-goog