[PATCH v2] ft: fix double free when disconnecting mid-FT

[PATCH v2] ft: fix double free when disconnecting mid-FT

[James Prestwood]

If IWD gets a disconnect during FT the roaming state will be
cleared, as well as any ft_info's during ft_clear_authentications.
This includes canceling the offchannel operation which also
destroys any pending ft_info's if !info->parsed. This causes a
double free afterwards. Knowning this, check the status of the
ft_info and only free if it has been parsed.

Log and crash backtrace below:

iwd[488]: src/station.c:station_try_next_transition() 5, target aa:46:8d:37:7c:87
iwd[488]: src/wiphy.c:wiphy_radio_work_insert() Inserting work item 16668
iwd[488]: src/wiphy.c:wiphy_radio_work_insert() Inserting work item 16669
iwd[488]: src/wiphy.c:wiphy_radio_work_done() Work item 16667 done
iwd[488]: src/wiphy.c:wiphy_radio_work_next() Starting work item 16668
iwd[488]: src/netdev.c:netdev_mlme_notify() MLME notification Remain on Channel(55)
iwd[488]: src/netdev.c:netdev_mlme_notify() MLME notification Del Station(20)
iwd[488]: src/netdev.c:netdev_link_notify() event 16 on ifindex 5
iwd[488]: src/netdev.c:netdev_mlme_notify() MLME notification Deauthenticate(39)
iwd[488]: src/netdev.c:netdev_deauthenticate_event()
iwd[488]: src/netdev.c:netdev_mlme_notify() MLME notification Disconnect(48)
iwd[488]: src/netdev.c:netdev_disconnect_event()
iwd[488]: Received Deauthentication event, reason: 6, from_ap: true
iwd[488]: src/station.c:station_disconnect_event() 5
iwd[488]: src/station.c:station_disassociated() 5
iwd[488]: src/station.c:station_reset_connection_state() 5
iwd[488]: src/station.c:station_roam_state_clear() 5
iwd[488]: double free or corruption (fasttop)

5  0x0000555b3dbf44a4 in ft_info_destroy ()
6  0x0000555b3dbf45b3 in remove_ifindex ()
7  0x0000555b3dc4653c in l_queue_foreach_remove ()
8  0x0000555b3dbd0dd1 in station_reset_connection_state ()
9  0x0000555b3dbd37e5 in station_disassociated ()
10 0x0000555b3dbc8bb8 in netdev_mlme_notify ()
11 0x0000555b3dc4e80b in received_data ()
12 0x0000555b3dc4b430 in io_callback ()
13 0x0000555b3dc4a5ed in l_main_iterate ()
14 0x0000555b3dc4a6bc in l_main_run ()
15 0x0000555b3dc4a8e0 in l_main_run_with_signal ()
16 0x0000555b3dbbe888 in main ()
---
 src/ft.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

v2:
 * This was missing the check for the offchannel_id as well. If there is
   not a current offchannel operation the info needs to be freed as
   well (not only when info->parsed == true).

diff --git a/src/ft.c b/src/ft.c
index 8ae683a7..e7794bf5 100644
--- a/src/ft.c
+++ b/src/ft.c
@@ -1175,6 +1175,7 @@ static bool remove_ifindex(void *data, void *user_data)
 {
 	struct ft_info *info = data;
 	uint32_t ifindex = L_PTR_TO_UINT(user_data);
+	bool need_free = info->parsed || !info->offchannel_id;
 
 	if (info->ifindex != ifindex)
 		return false;
@@ -1183,7 +1184,15 @@ static bool remove_ifindex(void *data, void *user_data)
 		offchannel_cancel(netdev_get_wdev_id(netdev_find(ifindex)),
 					info->offchannel_id);
 
-	ft_info_destroy(info);
+	/*
+	 * If we hadn't yet got an authenticate response or there was something
+	 * wrong with parsing (i.e. !info->parsed) the offchannel destroy
+	 * callback will end up destroying the info. Otherwise we need to
+	 * destroy it here.
+	 */
+	if (need_free)
+		ft_info_destroy(info);
+
 	return true;
 }
 
-- 
2.25.1

Re: [PATCH v2] ft: fix double free when disconnecting mid-FT

[Denis Kenzior]

Hi James,

On 4/19/23 15:30, James Prestwood wrote:
> If IWD gets a disconnect during FT the roaming state will be
> cleared, as well as any ft_info's during ft_clear_authentications.
> This includes canceling the offchannel operation which also
> destroys any pending ft_info's if !info->parsed. This causes a
> double free afterwards. Knowning this, check the status of the
> ft_info and only free if it has been parsed.
> 
> Log and crash backtrace below:
> 
> iwd[488]: src/station.c:station_try_next_transition() 5, target aa:46:8d:37:7c:87
> iwd[488]: src/wiphy.c:wiphy_radio_work_insert() Inserting work item 16668
> iwd[488]: src/wiphy.c:wiphy_radio_work_insert() Inserting work item 16669
> iwd[488]: src/wiphy.c:wiphy_radio_work_done() Work item 16667 done
> iwd[488]: src/wiphy.c:wiphy_radio_work_next() Starting work item 16668
> iwd[488]: src/netdev.c:netdev_mlme_notify() MLME notification Remain on Channel(55)
> iwd[488]: src/netdev.c:netdev_mlme_notify() MLME notification Del Station(20)
> iwd[488]: src/netdev.c:netdev_link_notify() event 16 on ifindex 5
> iwd[488]: src/netdev.c:netdev_mlme_notify() MLME notification Deauthenticate(39)
> iwd[488]: src/netdev.c:netdev_deauthenticate_event()
> iwd[488]: src/netdev.c:netdev_mlme_notify() MLME notification Disconnect(48)
> iwd[488]: src/netdev.c:netdev_disconnect_event()
> iwd[488]: Received Deauthentication event, reason: 6, from_ap: true
> iwd[488]: src/station.c:station_disconnect_event() 5
> iwd[488]: src/station.c:station_disassociated() 5
> iwd[488]: src/station.c:station_reset_connection_state() 5
> iwd[488]: src/station.c:station_roam_state_clear() 5
> iwd[488]: double free or corruption (fasttop)
> 
> 5  0x0000555b3dbf44a4 in ft_info_destroy ()
> 6  0x0000555b3dbf45b3 in remove_ifindex ()
> 7  0x0000555b3dc4653c in l_queue_foreach_remove ()
> 8  0x0000555b3dbd0dd1 in station_reset_connection_state ()
> 9  0x0000555b3dbd37e5 in station_disassociated ()
> 10 0x0000555b3dbc8bb8 in netdev_mlme_notify ()
> 11 0x0000555b3dc4e80b in received_data ()
> 12 0x0000555b3dc4b430 in io_callback ()
> 13 0x0000555b3dc4a5ed in l_main_iterate ()
> 14 0x0000555b3dc4a6bc in l_main_run ()
> 15 0x0000555b3dc4a8e0 in l_main_run_with_signal ()
> 16 0x0000555b3dbbe888 in main ()
> ---
>   src/ft.c | 11 ++++++++++-
>   1 file changed, 10 insertions(+), 1 deletion(-)
> 
> v2:
>   * This was missing the check for the offchannel_id as well. If there is
>     not a current offchannel operation the info needs to be freed as
>     well (not only when info->parsed == true).
> 
> diff --git a/src/ft.c b/src/ft.c
> index 8ae683a7..e7794bf5 100644
> --- a/src/ft.c
> +++ b/src/ft.c
> @@ -1175,6 +1175,7 @@ static bool remove_ifindex(void *data, void *user_data)
>   {
>   	struct ft_info *info = data;
>   	uint32_t ifindex = L_PTR_TO_UINT(user_data);
> +	bool need_free = info->parsed || !info->offchannel_id;

If offchannel_id is true, then info->parsed is false, no?

>   
>   	if (info->ifindex != ifindex)
>   		return false;
> @@ -1183,7 +1184,15 @@ static bool remove_ifindex(void *data, void *user_data)
>   		offchannel_cancel(netdev_get_wdev_id(netdev_find(ifindex)),
>   					info->offchannel_id);
>   
> -	ft_info_destroy(info);
> +	/*
> +	 * If we hadn't yet got an authenticate response or there was something
> +	 * wrong with parsing (i.e. !info->parsed) the offchannel destroy
> +	 * callback will end up destroying the info. Otherwise we need to
> +	 * destroy it here.
> +	 */
> +	if (need_free)
> +		ft_info_destroy(info);
> +

So I would write this as:

if (info->offchannel_id)
	offchannel_cancel
else
	ft_info_destroy(...);

However, I'm pretty sure this patch is not fixing anything but just trading one 
double-free for another.  offchannel_cancel results in ft_authenticate_destroy 
being called, which in turn results in l_queue_remove().  remove_ifindex() is 
called from inside l_queue_foreach_remove(), and you can't call l_queue_remove() 
on the same queue inside the foreach callback.

Regards,
-Denis