From cfb49616cdeb02c7cbb3dd314c55b9452ee21182 Mon Sep 17 00:00:00 2001
From: Richard Yao <richard.yao@alumni.stonybrook.edu>
Date: Mon, 23 Jan 2023 15:03:21 -0500
Subject: [PATCH] Cleanup: spa vdev processing should check NULL pointers

The PVS Studio 2016 FreeBSD kernel report stated:

\contrib\opensolaris\uts\common\fs\zfs\spa.c (1341): error V595: The 'spa->spa_spares.sav_vdevs' pointer was utilized before it was verified against nullptr. Check lines: 1341, 1342.
\sys\cddl\contrib\opensolaris\uts\common\fs\zfs\spa.c (1355): error V595: The 'spa->spa_l2cache.sav_vdevs' pointer was utilized before it was verified against nullptr. Check lines: 1355, 1357.
\sys\cddl\contrib\opensolaris\uts\common\fs\zfs\spa.c (1398): error V595: The 'spa->spa_spares.sav_vdevs' pointer was utilized before it was verified against nullptr. Check lines: 1398, 1408.
\sys\cddl\contrib\opensolaris\uts\common\fs\zfs\spa.c (1583): error V595: The 'oldvdevs' pointer was utilized before it was verified against nullptr. Check lines: 1583, 1595.

In practice, all of these uses were safe because a NULL pointer
implied a 0 vdev count, which kept us from iterating over vdevs.
However, rearranging the code to check the pointer first is not a
terrible micro-optimization and makes it more readable, so let us
do that.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Brian Atkinson <batkinson@lanl.gov>
Signed-off-by: Richard Yao <richard.yao@alumni.stonybrook.edu>
Closes #14456
---
 module/zfs/spa.c | 58 +++++++++++++++++++++++++-----------------------
 1 file changed, 30 insertions(+), 28 deletions(-)

diff --git a/module/zfs/spa.c b/module/zfs/spa.c
index 67b3a03a95..bbb83fc610 100644
--- a/module/zfs/spa.c
+++ b/module/zfs/spa.c
@@ -1714,9 +1714,9 @@ spa_unload(spa_t *spa)
 	 */
 	spa_l2cache_drop(spa);
 
-	for (int i = 0; i < spa->spa_spares.sav_count; i++)
-		vdev_free(spa->spa_spares.sav_vdevs[i]);
 	if (spa->spa_spares.sav_vdevs) {
+		for (int i = 0; i < spa->spa_spares.sav_count; i++)
+			vdev_free(spa->spa_spares.sav_vdevs[i]);
 		kmem_free(spa->spa_spares.sav_vdevs,
 		    spa->spa_spares.sav_count * sizeof (void *));
 		spa->spa_spares.sav_vdevs = NULL;
@@ -1727,11 +1727,11 @@ spa_unload(spa_t *spa)
 	}
 	spa->spa_spares.sav_count = 0;
 
-	for (int i = 0; i < spa->spa_l2cache.sav_count; i++) {
-		vdev_clear_stats(spa->spa_l2cache.sav_vdevs[i]);
-		vdev_free(spa->spa_l2cache.sav_vdevs[i]);
-	}
 	if (spa->spa_l2cache.sav_vdevs) {
+		for (int i = 0; i < spa->spa_l2cache.sav_count; i++) {
+			vdev_clear_stats(spa->spa_l2cache.sav_vdevs[i]);
+			vdev_free(spa->spa_l2cache.sav_vdevs[i]);
+		}
 		kmem_free(spa->spa_l2cache.sav_vdevs,
 		    spa->spa_l2cache.sav_count * sizeof (void *));
 		spa->spa_l2cache.sav_vdevs = NULL;
@@ -1789,20 +1789,21 @@ spa_load_spares(spa_t *spa)
 	/*
 	 * First, close and free any existing spare vdevs.
 	 */
-	for (i = 0; i < spa->spa_spares.sav_count; i++) {
-		vd = spa->spa_spares.sav_vdevs[i];
+	if (spa->spa_spares.sav_vdevs) {
+		for (i = 0; i < spa->spa_spares.sav_count; i++) {
+			vd = spa->spa_spares.sav_vdevs[i];
 
-		/* Undo the call to spa_activate() below */
-		if ((tvd = spa_lookup_by_guid(spa, vd->vdev_guid,
-		    B_FALSE)) != NULL && tvd->vdev_isspare)
-			spa_spare_remove(tvd);
-		vdev_close(vd);
-		vdev_free(vd);
-	}
+			/* Undo the call to spa_activate() below */
+			if ((tvd = spa_lookup_by_guid(spa, vd->vdev_guid,
+			    B_FALSE)) != NULL && tvd->vdev_isspare)
+				spa_spare_remove(tvd);
+			vdev_close(vd);
+			vdev_free(vd);
+		}
 
-	if (spa->spa_spares.sav_vdevs)
 		kmem_free(spa->spa_spares.sav_vdevs,
 		    spa->spa_spares.sav_count * sizeof (void *));
+	}
 
 	if (spa->spa_spares.sav_config == NULL)
 		nspares = 0;
@@ -2013,23 +2014,24 @@ out:
 	/*
 	 * Purge vdevs that were dropped
 	 */
-	for (i = 0; i < oldnvdevs; i++) {
-		uint64_t pool;
+	if (oldvdevs) {
+		for (i = 0; i < oldnvdevs; i++) {
+			uint64_t pool;
 
-		vd = oldvdevs[i];
-		if (vd != NULL) {
-			ASSERT(vd->vdev_isl2cache);
+			vd = oldvdevs[i];
+			if (vd != NULL) {
+				ASSERT(vd->vdev_isl2cache);
 
-			if (spa_l2cache_exists(vd->vdev_guid, &pool) &&
-			    pool != 0ULL && l2arc_vdev_present(vd))
-				l2arc_remove_vdev(vd);
-			vdev_clear_stats(vd);
-			vdev_free(vd);
+				if (spa_l2cache_exists(vd->vdev_guid, &pool) &&
+				    pool != 0ULL && l2arc_vdev_present(vd))
+					l2arc_remove_vdev(vd);
+				vdev_clear_stats(vd);
+				vdev_free(vd);
+			}
 		}
-	}
 
-	if (oldvdevs)
 		kmem_free(oldvdevs, oldnvdevs * sizeof (void *));
+	}
 
 	for (i = 0; i < sav->sav_count; i++)
 		nvlist_free(l2cache[i]);