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

["Christoph Böhmwalder" <christoph.boehmwalder@linbit.com>]

Am 15.11.22 um 14:16 schrieb 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@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);

Thanks!

Reviewed-by: Christoph Böhmwalder <christoph.boehmwalder@linbit.com>

-- 
Christoph Böhmwalder
LINBIT | Keeping the Digital World Running
DRBD HA —  Disaster Recovery — Software defined Storage