xfs: check if an open file is on the health monitored fs

Create a new ioctl for the healthmon file that checks that a given fd
points to the same filesystem that the healthmon file is monitoring.
This allows xfs_healer to check that when it reopens a mountpoint to
perform repairs, the file that it gets matches the filesystem that
generated the corruption report.

(Note that xfs_healer doesn't maintain an open fd to a filesystem that
it's monitoring so that it doesn't pin the mount.)

Signed-off-by: "Darrick J. Wong" <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>

Author: Darrick J. Wong

fs/xfs/libxfs/xfs_fs.h

@@ -1151,6 +1151,15 @@ struct xfs_health_monitor {
 /* Initial return format version */
 #define XFS_HEALTH_MONITOR_FMT_V0	(0)
 
+/*
+ * Check that a given fd points to the same filesystem that the health monitor
+ * is monitoring.
+ */
+struct xfs_health_file_on_monitored_fs {
+	__s32		fd;
+	__u32		flags;	/* zero for now */
+};
+
 /*
  * ioctl commands that are used by Linux filesystems
  */
@@ -1191,7 +1200,8 @@ struct xfs_health_monitor {
 #define XFS_IOC_SCRUBV_METADATA	_IOWR('X', 64, struct xfs_scrub_vec_head)
 #define XFS_IOC_RTGROUP_GEOMETRY _IOWR('X', 65, struct xfs_rtgroup_geometry)
 #define XFS_IOC_HEALTH_MONITOR	_IOW ('X', 68, struct xfs_health_monitor)
-
+#define XFS_IOC_HEALTH_FD_ON_MONITORED_FS \
+				_IOW ('X', 69, struct xfs_health_file_on_monitored_fs)
 /*
  * ioctl commands that replace IRIX syssgi()'s
  */

fs/xfs/xfs_healthmon.c

@@ -1090,6 +1090,38 @@ xfs_healthmon_reconfigure(
 	return 0;
 }
 
+/* Does the fd point to the same filesystem as the one we're monitoring? */
+STATIC long
+xfs_healthmon_file_on_monitored_fs(
+	struct file			*file,
+	unsigned int			cmd,
+	void __user			*arg)
+{
+	struct xfs_health_file_on_monitored_fs hms;
+	struct xfs_healthmon		*hm = file->private_data;
+	struct inode			*hms_inode;
+
+	if (copy_from_user(&hms, arg, sizeof(hms)))
+		return -EFAULT;
+
+	if (hms.flags)
+		return -EINVAL;
+
+	CLASS(fd, hms_fd)(hms.fd);
+	if (fd_empty(hms_fd))
+		return -EBADF;
+
+	hms_inode = file_inode(fd_file(hms_fd));
+	mutex_lock(&hm->lock);
+	if (hm->mount_cookie != (uintptr_t)hms_inode->i_sb) {
+		mutex_unlock(&hm->lock);
+		return -ESTALE;
+	}
+
+	mutex_unlock(&hm->lock);
+	return 0;
+}
+
 /* Handle ioctls for the health monitoring thread. */
 STATIC long
 xfs_healthmon_ioctl(
@@ -1102,6 +1134,8 @@ xfs_healthmon_ioctl(
 	switch (cmd) {
 	case XFS_IOC_HEALTH_MONITOR:
 		return xfs_healthmon_reconfigure(file, cmd, arg);
+	case XFS_IOC_HEALTH_FD_ON_MONITORED_FS:
+		return xfs_healthmon_file_on_monitored_fs(file, cmd, arg);
 	default:
 		break;
 	}