LSM: Add security_path_chroot().

This patch allows pathname based LSM modules to check chroot() operations.

This hook is used by TOMOYO.

Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Signed-off-by: James Morris <jmorris@namei.org>

fs/open.c

@@ -587,6 +587,9 @@ SYSCALL_DEFINE1(chroot, const char __user *, filename)
 	error = -EPERM;
 	if (!capable(CAP_SYS_CHROOT))
 		goto dput_and_out;
+	error = security_path_chroot(&path);
+	if (error)
+		goto dput_and_out;
 
 	set_fs_root(current->fs, &path);
 	error = 0;

include/linux/security.h

@@ -459,6 +459,10 @@ static inline void security_free_mnt_opts(struct security_mnt_opts *opts)
  *	@uid contains new owner's ID.
  *	@gid contains new group's ID.
  *	Return 0 if permission is granted.
+ * @path_chroot:
+ *	Check for permission to change root directory.
+ *	@path contains the path structure.
+ *	Return 0 if permission is granted.
  * @inode_readlink:
  *	Check the permission to read the symbolic link.
  *	@dentry contains the dentry structure for the file link.
@@ -1503,6 +1507,7 @@ struct security_operations {
 	int (*path_chmod) (struct dentry *dentry, struct vfsmount *mnt,
 			   mode_t mode);
 	int (*path_chown) (struct path *path, uid_t uid, gid_t gid);
+	int (*path_chroot) (struct path *path);
 #endif
 
 	int (*inode_alloc_security) (struct inode *inode);
@@ -2970,6 +2975,7 @@ int security_path_rename(struct path *old_dir, struct dentry *old_dentry,
 int security_path_chmod(struct dentry *dentry, struct vfsmount *mnt,
 			mode_t mode);
 int security_path_chown(struct path *path, uid_t uid, gid_t gid);
+int security_path_chroot(struct path *path);
 #else	/* CONFIG_SECURITY_PATH */
 static inline int security_path_unlink(struct path *dir, struct dentry *dentry)
 {
@@ -3031,6 +3037,11 @@ static inline int security_path_chown(struct path *path, uid_t uid, gid_t gid)
 {
 	return 0;
 }
+
+static inline int security_path_chroot(struct path *path)
+{
+	return 0;
+}
 #endif	/* CONFIG_SECURITY_PATH */
 
 #ifdef CONFIG_KEYS

security/capability.c

@@ -319,6 +319,11 @@ static int cap_path_chown(struct path *path, uid_t uid, gid_t gid)
 {
 	return 0;
 }
+
+static int cap_path_chroot(struct path *root)
+{
+	return 0;
+}
 #endif
 
 static int cap_file_permission(struct file *file, int mask)
@@ -990,6 +995,7 @@ void security_fixup_ops(struct security_operations *ops)
 	set_to_cap_if_null(ops, path_truncate);
 	set_to_cap_if_null(ops, path_chmod);
 	set_to_cap_if_null(ops, path_chown);
+	set_to_cap_if_null(ops, path_chroot);
 #endif
 	set_to_cap_if_null(ops, file_permission);
 	set_to_cap_if_null(ops, file_alloc_security);

security/security.c

@@ -449,6 +449,11 @@ int security_path_chown(struct path *path, uid_t uid, gid_t gid)
 		return 0;
 	return security_ops->path_chown(path, uid, gid);
 }
+
+int security_path_chroot(struct path *path)
+{
+	return security_ops->path_chroot(path);
+}
 #endif
 
 int security_inode_create(struct inode *dir, struct dentry *dentry, int mode)