Re: [PATCH 1/1] of: property: Fix device_node cleanup

[Neil Armstrong <neil.armstrong@linaro.org>]

On 29/05/2024 09:32, Alexander Stein wrote:
> '__free(device_node)' attached to remote will cause a double release:
>> OF: ERROR: of_node_release() detected bad of_node_put() on
>> /soc@0/bus@32c00000/dsi@32e60000
> 
> In case remote is to be returned it must not be cleaned up by a call
> to of_node_put. The caller has to do that as the documentation mentions.
> Partly revert commit b94d24c08ee1a ("of: property: Remove calls to
> of_node_put") to fix it.
> 
> Fixes: b94d24c08ee1 ("of: property: Remove calls to of_node_put")
> Signed-off-by: Alexander Stein <alexander.stein@ew.tq-group.com>
> ---
> I get the following trace starting with next-20240529:
> 
> OF: ERROR: of_node_release() detected bad of_node_put() on /soc@0/bus@32c00000/dsi@32e60000
> CPU: 0 PID: 11 Comm: kworker/u16:0 Not tainted 6.10.0-rc1-next-20240529+ #2511 610eecbb638fc5fab9a27e01b78203e8a379a280
> Hardware name: TQ-Systems i.MX8MPlus TQMa8MPxL on MBa8MPxL (DT)
> Workqueue: events_unbound deferred_probe_work_func
> Call trace:
>   dump_backtrace+0x90/0x10c
>   show_stack+0x14/0x1c
>   dump_stack_lvl+0x6c/0x80
>   dump_stack+0x14/0x1c
>   of_node_release+0x11c/0x188
>   kobject_cleanup+0x48/0x17c
>   kobject_put+0x78/0xc0
>   of_node_put+0x14/0x20
>   drm_of_find_panel_or_bridge+0x84/0xd4
>   devm_drm_of_get_bridge+0x3c/0x8c
>   lcdif_attach_bridge+0x88/0x270
>   lcdif_load+0x144/0x28c
>   lcdif_probe+0x34/0xcc
>   platform_probe+0x64/0xe8
>   really_probe+0xc8/0x3ac
>   __driver_probe_device+0x84/0x188
>   driver_probe_device+0x38/0x150
>   __device_attach_driver+0xcc/0x194
>   bus_for_each_drv+0x80/0xdc
>   __device_attach+0x9c/0x1d0
>   device_initial_probe+0x10/0x18
>   bus_probe_device+0xa4/0xa8
>   deferred_probe_work_func+0x9c/0xe8
>   process_one_work+0x154/0x3fc
>   worker_thread+0x2f4/0x404
>   kthread+0xf4/0x100
>   ret_from_fork+0x10/0x20
> OF: ERROR: next of_node_put() on this node will result in a kobject warning 'refcount_t: underflow; use-after-free.'
> ------------[ cut here ]------------
> refcount_t: addition on 0; use-after-free.
> WARNING: CPU: 0 PID: 11 at lib/refcount.c:25 refcount_warn_saturate+0x150/0x214
> Modules linked in:
> CPU: 0 PID: 11 Comm: kworker/u16:0 Not tainted 6.10.0-rc1-next-20240529+ #2511 610eecbb638fc5fab9a27e01b78203e8a379a280
> Hardware name: TQ-Systems i.MX8MPlus TQMa8MPxL on MBa8MPxL (DT)
> [...]
> 
>   drivers/of/property.c | 6 +++---
>   1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/of/property.c b/drivers/of/property.c
> index 83536216ed4fe..e5c6301643e4c 100644
> --- a/drivers/of/property.c
> +++ b/drivers/of/property.c
> @@ -836,9 +836,7 @@ struct device_node *of_graph_get_remote_node(const struct device_node *node,
>   {
>   	struct device_node *endpoint_node __free(device_node) =
>   			    of_graph_get_endpoint_by_regs(node, port, endpoint);
> -
> -	struct device_node *remote __free(device_node) =
> -			    of_graph_get_remote_port_parent(endpoint_node);
> +	struct device_node *remote;
>   
>   	if (!endpoint_node) {
>   		pr_debug("no valid endpoint (%d, %d) for node %pOF\n",
> @@ -846,6 +844,7 @@ struct device_node *of_graph_get_remote_node(const struct device_node *node,
>   		return NULL;
>   	}
>   
> +	remote = of_graph_get_remote_port_parent(endpoint_node);
>   	if (!remote) {
>   		pr_debug("no valid remote node\n");
>   		return NULL;
> @@ -853,6 +852,7 @@ struct device_node *of_graph_get_remote_node(const struct device_node *node,
>   
>   	if (!of_device_is_available(remote)) {
>   		pr_debug("not available for remote node\n");
> +		of_node_put(remote);
>   		return NULL;
>   	}
>   

Tested-by: Neil Armstrong <neil.armstrong@linaro.org> # on SM8650-QRD