zonefs: Detect append writes at invalid locations

Using REQ_OP_ZONE_APPEND operations for synchronous writes to sequential
files succeeds regardless of the zone write pointer position, as long as
the target zone is not full. This means that if an external (buggy)
application writes to the zone of a sequential file underneath the file
system, subsequent file write() operation will succeed but the file size
will not be correct and the file will contain invalid data written by
another application.

Modify zonefs_file_dio_append() to check the written sector of an append
write (returned in bio->bi_iter.bi_sector) and return -EIO if there is a
mismatch with the file zone wp offset field. This change triggers a call
to zonefs_io_error() and a zone check. Modify zonefs_io_error_cb() to
not expose the unexpected data after the current inode size when the
errors=remount-ro mode is used. Other error modes are correctly handled
already.

Fixes: 02ef12a ("zonefs: use REQ_OP_ZONE_APPEND for sync DIO")
Cc: [email protected]
Signed-off-by: Damien Le Moal <[email protected]>
Reviewed-by: Johannes Thumshirn <[email protected]>

fs/zonefs/super.c

@@ -442,6 +442,10 @@ static int zonefs_io_error_cb(struct blk_zone *zone, unsigned int idx,
 			data_size = zonefs_check_zone_condition(inode, zone,
 								false, false);
 		}
+	} else if (sbi->s_mount_opts & ZONEFS_MNTOPT_ERRORS_RO &&
+		   data_size > isize) {
+		/* Do not expose garbage data */
+		data_size = isize;
 	}
 
 	/*
@@ -805,6 +809,24 @@ static ssize_t zonefs_file_dio_append(struct kiocb *iocb, struct iov_iter *from)
 
 	ret = submit_bio_wait(bio);
 
+	/*
+	 * If the file zone was written underneath the file system, the zone
+	 * write pointer may not be where we expect it to be, but the zone
+	 * append write can still succeed. So check manually that we wrote where
+	 * we intended to, that is, at zi->i_wpoffset.
+	 */
+	if (!ret) {
+		sector_t wpsector =
+			zi->i_zsector + (zi->i_wpoffset >> SECTOR_SHIFT);
+
+		if (bio->bi_iter.bi_sector != wpsector) {
+			zonefs_warn(inode->i_sb,
+				"Corrupted write pointer %llu for zone at %llu\n",
+				wpsector, zi->i_zsector);
+			ret = -EIO;
+		}
+	}
+
 	zonefs_file_write_dio_end_io(iocb, size, ret, 0);
 	trace_zonefs_file_dio_append(inode, size, ret);