[Drbd-dev] [PATCH] drbd: use after free in drbd_create_device()

[Dan Carpenter]

The drbd_destroy_connection() frees the "connection" so use the _safe()
iterator to prevent a use after free.

Fixes: b6f85ef9538b ("drbd: Iterate over all connections")
Signed-off-by: Dan Carpenter <error27 at gmail.com>
---
Smatch assumes that kref_put() generally calls the free function so it
gets very confused by drbd_delete_device() which calls:

	kref_put(&device->kref, drbd_destroy_device);

Four times in a row.  (Smatch has some checking for incremented
reference counts but even there it assumes that people are going to hold
one reference and not four).

drivers/block/drbd/drbd_main.c:2831 drbd_delete_device() error: dereferencing freed memory 'device'
drivers/block/drbd/drbd_main.c:2833 drbd_delete_device() warn: passing freed memory 'device'
drivers/block/drbd/drbd_main.c:2835 drbd_delete_device() error: dereferencing freed memory 'device'

The drbd_adm_get_status_all() function makes me itch as well.  It seems
like we drop a reference and then take it again?

drivers/block/drbd/drbd_nl.c:4019 drbd_adm_get_status_all() warn: 'resource' was already freed.
drivers/block/drbd/drbd_nl.c:4021 drbd_adm_get_status_all() warn: 'resource' was already freed.

 drivers/block/drbd/drbd_main.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/block/drbd/drbd_main.c b/drivers/block/drbd/drbd_main.c
index f3e4db16fd07..8532b839a343 100644
--- a/drivers/block/drbd/drbd_main.c
+++ b/drivers/block/drbd/drbd_main.c
@@ -2672,7 +2672,7 @@ static int init_submitter(struct drbd_device *device)
 enum drbd_ret_code drbd_create_device(struct drbd_config_context *adm_ctx, unsigned int minor)
 {
 	struct drbd_resource *resource = adm_ctx->resource;
-	struct drbd_connection *connection;
+	struct drbd_connection *connection, *n;
 	struct drbd_device *device;
 	struct drbd_peer_device *peer_device, *tmp_peer_device;
 	struct gendisk *disk;
@@ -2789,7 +2789,7 @@ enum drbd_ret_code drbd_create_device(struct drbd_config_context *adm_ctx, unsig
 	return NO_ERROR;
 
 out_idr_remove_from_resource:
-	for_each_connection(connection, resource) {
+	for_each_connection_safe(connection, n, resource) {
 		peer_device = idr_remove(&connection->peer_devices, vnr);
 		if (peer_device)
 			kref_put(&connection->kref, drbd_destroy_connection);
-- 
2.35.1