xfs: capture inode generation numbers in the ondisk exchmaps log item

Per some very late review comments, capture the generation numbers of
both inodes involved in a file content exchange operation so that we
don't accidentally target files with have been reallocated.
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>

fs/xfs/libxfs/xfs_log_format.h

@@ -896,6 +896,8 @@ struct xfs_xmi_log_format {
 
 	uint64_t		xmi_inode1;	/* inumber of first file */
 	uint64_t		xmi_inode2;	/* inumber of second file */
+	uint32_t		xmi_igen1;	/* generation of first file */
+	uint32_t		xmi_igen2;	/* generation of second file */
 	uint64_t		xmi_startoff1;	/* block offset into file1 */
 	uint64_t		xmi_startoff2;	/* block offset into file2 */
 	uint64_t		xmi_blockcount;	/* number of blocks */

fs/xfs/libxfs/xfs_log_recover.h

@@ -123,6 +123,8 @@ bool xlog_is_buffer_cancelled(struct xlog *log, xfs_daddr_t blkno, uint len);
 
 int xlog_recover_iget(struct xfs_mount *mp, xfs_ino_t ino,
 		struct xfs_inode **ipp);
+int xlog_recover_iget_handle(struct xfs_mount *mp, xfs_ino_t ino, uint32_t gen,
+		struct xfs_inode **ipp);
 void xlog_recover_release_intent(struct xlog *log, unsigned short intent_type,
 		uint64_t intent_id);
 int xlog_alloc_buf_cancel_table(struct xlog *log);

fs/xfs/xfs_exchmaps_item.c

@@ -231,7 +231,9 @@ xfs_exchmaps_create_intent(
 	xlf = &xmi_lip->xmi_format;
 
 	xlf->xmi_inode1 = xmi->xmi_ip1->i_ino;
+	xlf->xmi_igen1 = VFS_I(xmi->xmi_ip1)->i_generation;
 	xlf->xmi_inode2 = xmi->xmi_ip2->i_ino;
+	xlf->xmi_igen2 = VFS_I(xmi->xmi_ip2)->i_generation;
 	xlf->xmi_startoff1 = xmi->xmi_startoff1;
 	xlf->xmi_startoff2 = xmi->xmi_startoff2;
 	xlf->xmi_blockcount = xmi->xmi_blockcount;
@@ -368,14 +370,25 @@ xfs_xmi_item_recover_intent(
 	/*
 	 * Grab both inodes and set IRECOVERY to prevent trimming of post-eof
 	 * mappings and freeing of unlinked inodes until we're totally done
-	 * processing files.
+	 * processing files.  The ondisk format of this new log item contains
+	 * file handle information, which is why recovery for other items do
+	 * not check the inode generation number.
 	 */
-	error = xlog_recover_iget(mp, xlf->xmi_inode1, &ip1);
-	if (error)
+	error = xlog_recover_iget_handle(mp, xlf->xmi_inode1, xlf->xmi_igen1,
+			&ip1);
+	if (error) {
+		XFS_CORRUPTION_ERROR(__func__, XFS_ERRLEVEL_LOW, mp, xlf,
+				sizeof(*xlf));
 		return ERR_PTR(error);
-	error = xlog_recover_iget(mp, xlf->xmi_inode2, &ip2);
-	if (error)
+	}
+
+	error = xlog_recover_iget_handle(mp, xlf->xmi_inode2, xlf->xmi_igen2,
+			&ip2);
+	if (error) {
+		XFS_CORRUPTION_ERROR(__func__, XFS_ERRLEVEL_LOW, mp, xlf,
+				sizeof(*xlf));
 		goto err_rele1;
+	}
 
 	req->ip1 = ip1;
 	req->ip2 = ip2;
@@ -485,6 +498,8 @@ xfs_exchmaps_relog_intent(
 
 	new_xlf->xmi_inode1	= old_xlf->xmi_inode1;
 	new_xlf->xmi_inode2	= old_xlf->xmi_inode2;
+	new_xlf->xmi_igen1	= old_xlf->xmi_igen1;
+	new_xlf->xmi_igen2	= old_xlf->xmi_igen2;
 	new_xlf->xmi_startoff1	= old_xlf->xmi_startoff1;
 	new_xlf->xmi_startoff2	= old_xlf->xmi_startoff2;
 	new_xlf->xmi_blockcount	= old_xlf->xmi_blockcount;

fs/xfs/xfs_log_recover.c

@@ -1767,6 +1767,37 @@ xlog_recover_iget(
 	return 0;
 }
 
+/*
+ * Get an inode so that we can recover a log operation.
+ *
+ * Log intent items that target inodes effectively contain a file handle.
+ * Check that the generation number matches the intent item like we do for
+ * other file handles.  Log intent items defined after this validation weakness
+ * was identified must use this function.
+ */
+int
+xlog_recover_iget_handle(
+	struct xfs_mount	*mp,
+	xfs_ino_t		ino,
+	uint32_t		gen,
+	struct xfs_inode	**ipp)
+{
+	struct xfs_inode	*ip;
+	int			error;
+
+	error = xlog_recover_iget(mp, ino, &ip);
+	if (error)
+		return error;
+
+	if (VFS_I(ip)->i_generation != gen) {
+		xfs_irele(ip);
+		return -EFSCORRUPTED;
+	}
+
+	*ipp = ip;
+	return 0;
+}
+
 /******************************************************************************
  *
  *		Log recover routines