ovl: stack fileattr ops

Add stacking for the fileattr operations.

Add hack for calling security_file_ioctl() for now.  Probably better to
have a pair of specific hooks for these operations.
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

fs/overlayfs/dir.c

@@ -1301,4 +1301,6 @@ const struct inode_operations ovl_dir_inode_operations = {
 	.listxattr	= ovl_listxattr,
 	.get_acl	= ovl_get_acl,
 	.update_time	= ovl_update_time,
+	.fileattr_get	= ovl_fileattr_get,
+	.fileattr_set	= ovl_fileattr_set,
 };

fs/overlayfs/inode.c

@@ -11,6 +11,8 @@
 #include <linux/posix_acl.h>
 #include <linux/ratelimit.h>
 #include <linux/fiemap.h>
+#include <linux/fileattr.h>
+#include <linux/security.h>
 #include "overlayfs.h"
 
 
@@ -500,6 +502,79 @@ static int ovl_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo,
 	return err;
 }
 
+/*
+ * Work around the fact that security_file_ioctl() takes a file argument.
+ * Introducing security_inode_fileattr_get/set() hooks would solve this issue
+ * properly.
+ */
+static int ovl_security_fileattr(struct dentry *dentry, struct fileattr *fa,
+				 bool set)
+{
+	struct path realpath;
+	struct file *file;
+	unsigned int cmd;
+	int err;
+
+	ovl_path_real(dentry, &realpath);
+	file = dentry_open(&realpath, O_RDONLY, current_cred());
+	if (IS_ERR(file))
+		return PTR_ERR(file);
+
+	if (set)
+		cmd = fa->fsx_valid ? FS_IOC_FSSETXATTR : FS_IOC_SETFLAGS;
+	else
+		cmd = fa->fsx_valid ? FS_IOC_FSGETXATTR : FS_IOC_GETFLAGS;
+
+	err = security_file_ioctl(file, cmd, 0);
+	fput(file);
+
+	return err;
+}
+
+int ovl_fileattr_set(struct user_namespace *mnt_userns,
+		     struct dentry *dentry, struct fileattr *fa)
+{
+	struct inode *inode = d_inode(dentry);
+	struct dentry *upperdentry;
+	const struct cred *old_cred;
+	int err;
+
+	err = ovl_want_write(dentry);
+	if (err)
+		goto out;
+
+	err = ovl_copy_up(dentry);
+	if (!err) {
+		upperdentry = ovl_dentry_upper(dentry);
+
+		old_cred = ovl_override_creds(inode->i_sb);
+		err = ovl_security_fileattr(dentry, fa, true);
+		if (!err)
+			err = vfs_fileattr_set(&init_user_ns, upperdentry, fa);
+		revert_creds(old_cred);
+		ovl_copyflags(ovl_inode_real(inode), inode);
+	}
+	ovl_drop_write(dentry);
+out:
+	return err;
+}
+
+int ovl_fileattr_get(struct dentry *dentry, struct fileattr *fa)
+{
+	struct inode *inode = d_inode(dentry);
+	struct dentry *realdentry = ovl_dentry_real(dentry);
+	const struct cred *old_cred;
+	int err;
+
+	old_cred = ovl_override_creds(inode->i_sb);
+	err = ovl_security_fileattr(dentry, fa, false);
+	if (!err)
+		err = vfs_fileattr_get(realdentry, fa);
+	revert_creds(old_cred);
+
+	return err;
+}
+
 static const struct inode_operations ovl_file_inode_operations = {
 	.setattr	= ovl_setattr,
 	.permission	= ovl_permission,
@@ -508,6 +583,8 @@ static const struct inode_operations ovl_file_inode_operations = {
 	.get_acl	= ovl_get_acl,
 	.update_time	= ovl_update_time,
 	.fiemap		= ovl_fiemap,
+	.fileattr_get	= ovl_fileattr_get,
+	.fileattr_set	= ovl_fileattr_set,
 };
 
 static const struct inode_operations ovl_symlink_inode_operations = {

fs/overlayfs/overlayfs.h

@@ -521,6 +521,9 @@ int __init ovl_aio_request_cache_init(void);
 void ovl_aio_request_cache_destroy(void);
 long ovl_ioctl(struct file *file, unsigned int cmd, unsigned long arg);
 long ovl_compat_ioctl(struct file *file, unsigned int cmd, unsigned long arg);
+int ovl_fileattr_get(struct dentry *dentry, struct fileattr *fa);
+int ovl_fileattr_set(struct user_namespace *mnt_userns,
+		     struct dentry *dentry, struct fileattr *fa);
 
 /* copy_up.c */
 int ovl_copy_up(struct dentry *dentry);