svn commit: r355325 - head/lib/libdevstat

[Andriy Gapon]

Author: avg
Date: Tue Dec  3 09:48:43 2019
New Revision: 355325
URL: https://svnweb.freebsd.org/changeset/base/355325

Log:
  devstat_selectdevs: resize dev_select only after copying data out of it
  
  The resizing could be a downsizing so some data would be lost and we
  could attempt to read past the end of the new memory allocation.
  
  MFC after:	2 weeks
  Sponsored by:	Panzura

Modified:
  head/lib/libdevstat/devstat.c

Modified: head/lib/libdevstat/devstat.c
==============================================================================
--- head/lib/libdevstat/devstat.c	Tue Dec  3 09:12:53 2019	(r355324)
+++ head/lib/libdevstat/devstat.c	Tue Dec  3 09:48:43 2019	(r355325)
@@ -584,10 +584,10 @@ devstat_selectdevs(struct device_selection **dev_selec
 	 * In this case, we have selected devices before, but the device
 	 * list has changed since we last selected devices, so we need to
 	 * either enlarge or reduce the size of the device selection list.
+	 * But delay the resizing until after copying the data to old_dev_select
+	 * as to not lose any data in the case of reducing the size.
 	 */
 	} else if (*num_selections != numdevs) {
-		*dev_select = (struct device_selection *)reallocf(*dev_select,
-			numdevs * sizeof(struct device_selection));
 		*select_generation = current_generation;
 		init_selections = 1;
 	/*
@@ -643,6 +643,11 @@ devstat_selectdevs(struct device_selection **dev_selec
 		old_num_selections = *num_selections;
 		bcopy(*dev_select, old_dev_select, 
 		    sizeof(struct device_selection) * *num_selections);
+	}
+
+	if (!changed && *num_selections != numdevs) {
+		*dev_select = (struct device_selection *)reallocf(*dev_select,
+			numdevs * sizeof(struct device_selection));
 	}
 
 	if (init_selections != 0) {