[PATCH 2/3] drbd: fix an invalid memory access caused by incorrect use of list iterator

[Christoph Böhmwalder]

From: Xiaomeng Tong <xiam0nd.tong@xxxxxxxxx>

The bug is here:
	idr_remove(&connection->peer_devices, vnr);

If the previous for_each_connection() don't exit early (no goto hit
inside the loop), the iterator 'connection' after the loop will be a
bogus pointer to an invalid structure object containing the HEAD
(&resource->connections). As a result, the use of 'connection' above
will lead to a invalid memory access (including a possible invalid free
as idr_remove could call free_layer).

The original intention should have been to remove all peer_devices,
but the following lines have already done the work. So just remove
this line and the unneeded label, to fix this bug.

Cc: stable@xxxxxxxxxxxxxxx
Fixes: c06ece6ba6f1b ("drbd: Turn connection->volumes into connection->peer_devices")
Signed-off-by: Xiaomeng Tong <xiam0nd.tong@xxxxxxxxx>
Reviewed-by: Christoph Böhmwalder <christoph.boehmwalder@xxxxxxxxxx>
Reviewed-by: Lars Ellenberg <lars.ellenberg@xxxxxxxxxx>
---
 drivers/block/drbd/drbd_main.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/drivers/block/drbd/drbd_main.c b/drivers/block/drbd/drbd_main.c
index 9676a1d214bc..d6dfa286ddb3 100644
--- a/drivers/block/drbd/drbd_main.c
+++ b/drivers/block/drbd/drbd_main.c
@@ -2773,12 +2773,12 @@ enum drbd_ret_code drbd_create_device(struct drbd_config_context *adm_ctx, unsig
 
 	if (init_submitter(device)) {
 		err = ERR_NOMEM;
-		goto out_idr_remove_vol;
+		goto out_idr_remove_from_resource;
 	}
 
 	err = add_disk(disk);
 	if (err)
-		goto out_idr_remove_vol;
+		goto out_idr_remove_from_resource;
 
 	/* inherit the connection state */
 	device->state.conn = first_connection(resource)->cstate;
@@ -2792,8 +2792,6 @@ enum drbd_ret_code drbd_create_device(struct drbd_config_context *adm_ctx, unsig
 	drbd_debugfs_device_add(device);
 	return NO_ERROR;
 
-out_idr_remove_vol:
-	idr_remove(&connection->peer_devices, vnr);
 out_idr_remove_from_resource:
 	for_each_connection(connection, resource) {
 		peer_device = idr_remove(&connection->peer_devices, vnr);
-- 
2.35.1