Re: [PATCH] usb: gadget: f_tcm: fix remaining nexus NULL dereferences

[Thinh Nguyen]

On Thu, Jun 04, 2026, Guangshuo Li wrote:
> The previous nexus NULL-dereference fix added checks to the normal
> command submission paths, but two UASP paths still dereference
> tpg->tpg_nexus without checking it first.
> 
> A TASK MANAGEMENT request reaches usbg_submit_tmr(), which fetches
> tvn_se_sess directly from tpg->tpg_nexus. The RC_OVERLAPPED_TAG path in
> usbg_cmd_work() does the same before walking sess_cmd_map for the active
> command with the same tag.
> 
> If userspace drops the nexus after the command is queued, these paths can
> observe a NULL tpg_nexus and crash before they can ignore the command like
> the already-fixed command paths do.
> 
> Check tpg_nexus in both remaining paths and use the checked local nexus
> before dereferencing tvn_se_sess.
> 
> Fixes: b9fde5073553 ("usb: gadget: f_tcm: Fix NULL pointer dereferences in nexus handling")
> Signed-off-by: Guangshuo Li <lgs201920130244@xxxxxxxxx>
> ---
>  drivers/usb/gadget/function/f_tcm.c | 22 ++++++++++++++++++++--
>  1 file changed, 20 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/usb/gadget/function/f_tcm.c b/drivers/usb/gadget/function/f_tcm.c
> index 34d9f49e9987..1717fdd1c466 100644
> --- a/drivers/usb/gadget/function/f_tcm.c
> +++ b/drivers/usb/gadget/function/f_tcm.c
> @@ -1188,12 +1188,21 @@ static void usbg_aborted_task(struct se_cmd *se_cmd);
>  
>  static void usbg_submit_tmr(struct usbg_cmd *cmd)
>  {
> +	struct tcm_usbg_nexus *tv_nexus;
>  	struct se_session *se_sess;
>  	struct se_cmd *se_cmd;
>  	int flags = TARGET_SCF_ACK_KREF;
>  
>  	se_cmd = &cmd->se_cmd;
> -	se_sess = cmd->fu->tpg->tpg_nexus->tvn_se_sess;
> +	tv_nexus = cmd->fu->tpg->tpg_nexus;
> +	if (!tv_nexus) {
> +		struct usb_gadget *gadget = fuas_to_gadget(cmd->fu);
> +
> +		dev_err(&gadget->dev, "Missing nexus for TMR, ignoring command\n");

This is called after usbg_get_cmd(). We need to cleanup the
sbitmap_queue and the hash (sbitmap_queue_clear and hash_del) before
returning.

> +		return;
> +	}
> +
> +	se_sess = tv_nexus->tvn_se_sess;
>  
>  	target_submit_tmr(se_cmd, se_sess,
>  			  cmd->response_iu.add_response_info,
> @@ -1271,12 +1280,21 @@ static void usbg_cmd_work(struct work_struct *work)
>  skip:
>  	if (cmd->tmr_rsp == RC_OVERLAPPED_TAG) {
>  		struct f_uas *fu = cmd->fu;
> +		struct tcm_usbg_nexus *tv_nexus;
>  		struct se_session *se_sess;
>  		struct uas_stream *stream = NULL;
>  		struct hlist_node *tmp;
>  		struct usbg_cmd *active_cmd = NULL;
>  
> -		se_sess = cmd->fu->tpg->tpg_nexus->tvn_se_sess;
> +		tv_nexus = fu->tpg->tpg_nexus;
> +		if (!tv_nexus) {

Same here. Also check for other if (!tv_nexus) checks.

Maybe we need a helper function to do this cleanup?

Thanks,
Thinh

> +			struct usb_gadget *gadget = fuas_to_gadget(fu);
> +
> +			dev_err(&gadget->dev, "Missing nexus for overlapped tag, ignoring command\n");
> +			return;
> +		}
> +
> +		se_sess = tv_nexus->tvn_se_sess;
>  
>  		hash_for_each_possible_safe(fu->stream_hash, stream, tmp, node, cmd->tag) {
>  			int i = stream - &fu->stream[0];
> -- 
> 2.43.0
>