[PATCH v2] net: ceph: make free_choose_arg_map() resilient to partial allocation

[Tuo Li <islituo@gmail.com>]

free_choose_arg_map() may dereference a NULL pointer if its caller fails
after a partial allocation.

For example, in decode_choose_args(), if allocation of arg_map->args
fails, execution jumps to the fail label and free_choose_arg_map() is
called. Since arg_map->size is updated to a non-zero value before memory
allocation, free_choose_arg_map() will iterate over arg_map->args and
dereference a NULL pointer.

To prevent this potential NULL pointer dereference and make
free_choose_arg_map() more resilient, add checks for pointers before
iterating.

Signed-off-by: Tuo Li <islituo@gmail.com>
---
v2:
* Add pointer checks before iterating in free_choose_arg_map(), instead of
  moving the arg_map->size assignment in decode_choose_args().
  Thanks to Viacheslav Dubeyko for pointing out the issue with the previous
  patch, and to Ilya Dryomov for the helpful advice.
---
 net/ceph/osdmap.c | 20 ++++++++++++--------
 1 file changed, 12 insertions(+), 8 deletions(-)

diff --git a/net/ceph/osdmap.c b/net/ceph/osdmap.c
index 34b3ab59602f..08157945af43 100644
--- a/net/ceph/osdmap.c
+++ b/net/ceph/osdmap.c
@@ -241,22 +241,26 @@ static struct crush_choose_arg_map *alloc_choose_arg_map(void)
 
 static void free_choose_arg_map(struct crush_choose_arg_map *arg_map)
 {
-	if (arg_map) {
-		int i, j;
+	int i, j;
+
+	if (!arg_map)
+		return;
 
-		WARN_ON(!RB_EMPTY_NODE(&arg_map->node));
+	WARN_ON(!RB_EMPTY_NODE(&arg_map->node));
 
+	if (arg_map->args) {
 		for (i = 0; i < arg_map->size; i++) {
 			struct crush_choose_arg *arg = &arg_map->args[i];
-
-			for (j = 0; j < arg->weight_set_size; j++)
-				kfree(arg->weight_set[j].weights);
-			kfree(arg->weight_set);
+			if (arg->weight_set) {
+				for (j = 0; j < arg->weight_set_size; j++)
+					kfree(arg->weight_set[j].weights);
+				kfree(arg->weight_set);
+			}
 			kfree(arg->ids);
 		}
 		kfree(arg_map->args);
-		kfree(arg_map);
 	}
+	kfree(arg_map);
 }
 
 DEFINE_RB_FUNCS(choose_arg_map, struct crush_choose_arg_map, choose_args_index,
-- 
2.48.1