Added fix for zpool get state segfaults with two or more vdevs (openzfs#15972). (openzfs#17213)

The problem was identified in handling of the zpool get state command
line arguments. A pointer vdev was used to point to the argv[1], and
its address set to cb.cb_vdevs.cb_names(pointer to array of strings)
so any increment to cb_names resulted in a segfault. Fix covers a
special case of root parameter at argv[1] and remaining cases are
handled by passing in the argv + 1, which allows cb_names iteration
of next command line arguments (vdevs).

Reviewed-by: Tony Hutter <hutter2@llnl.gov>
Reviewed-by: Attila Fülöp <attila@fueloep.org>

Signed-off-by: Syed Shahrukh Hussain <syed.shahrukh@ossrevival.org>

Author: Syed-Shahrukh-OSSRevival

cmd/zpool/zpool_main.c

@@ -12747,11 +12747,13 @@ zpool_do_get(int argc, char **argv)
 
 			if (strcmp(argv[1], "root") == 0)
 				vdev = strdup("root-0");
-			else
-				vdev = strdup(argv[1]);
 
 			/* ... and the rest are vdev names */
-			cb.cb_vdevs.cb_names = &vdev;
+			if (vdev == NULL)
+				cb.cb_vdevs.cb_names = argv + 1;
+			else
+				cb.cb_vdevs.cb_names = &vdev;
+
 			cb.cb_vdevs.cb_names_count = argc - 1;
 			cb.cb_type = ZFS_TYPE_VDEV;
 			argc = 1; /* One pool to process */