usb: gadget: f_tcm: synchronize delayed set_alt with teardown

The f_tcm set_alt() path defers endpoint setup to a work item and
completes the delayed status response from process context. The delayed
work uses f_tcm private state and may complete the setup request after
disconnect or function teardown has already moved on.

Cancel and drain the delayed set_alt work when the function is unbound or
freed. For disable paths, which are reached under the composite device
lock, use a small state machine and a non-sleeping cancellation path
instead of cancel_work_sync(). If the work is already running, mark it
cancelled and let the worker own the cleanup; otherwise tcm_disable() can
cancel the queued work and clean up immediately.

Also serialize the final delayed-status completion with the cancellation
check while holding the composite device lock. This prevents a disconnect
from clearing delayed_status while the worker is about to complete the
control request.

Validation reproduced this kernel report:
BUG: KASAN: slab-use-after-free in tcm_delayed_set_alt+0x6c/0xef0

Call Trace:
 <TASK>
 dump_stack_lvl+0x66/0xa0
 print_report+0xce/0x630
 ? tcm_delayed_set_alt+0x6c/0xef0
 ? srso_alias_return_thunk+0x5/0xfbef5
 ? __virt_addr_valid+0x188/0x320
 ? tcm_delayed_set_alt+0x6c/0xef0
 kasan_report+0xe0/0x110
 ? tcm_delayed_set_alt+0x6c/0xef0
 tcm_delayed_set_alt+0x6c/0xef0
 ? __pfx_tcm_delayed_set_alt+0x10/0x10
 ? process_one_work+0x4cb/0xb90
 ? rcu_is_watching+0x20/0x50
 ? tcm_delayed_set_alt+0x9/0xef0
 process_one_work+0x4d7/0xb90
 ? __pfx_process_one_work+0x10/0x10
 ? srso_alias_return_thunk+0x5/0xfbef5
 ? __list_add_valid_or_report+0x37/0xf0
 ? __pfx_tcm_delayed_set_alt+0x10/0x10
 ? srso_alias_return_thunk+0x5/0xfbef5
 worker_thread+0x2d8/0x570
 ? __pfx_worker_thread+0x10/0x10
 kthread+0x1ad/0x1f0
 ? __pfx_kthread+0x10/0x10
 ret_from_fork+0x3c9/0x540
 ? __pfx_ret_from_fork+0x10/0x10
 ? srso_alias_return_thunk+0x5/0xfbef5
 ? __switch_to+0x2e9/0x730
 ? __pfx_kthread+0x10/0x10
 ret_from_fork_asm+0x1a/0x30
 </TASK>

Allocated by task 544:
 kasan_save_stack+0x33/0x60
 kasan_save_track+0x14/0x30
 __kasan_kmalloc+0x8f/0xa0
 tcm_alloc+0x68/0x180
 usb_get_function+0x36/0x60
 config_usb_cfg_link+0x125/0x1b0
 configfs_symlink+0x322/0x890
 vfs_symlink+0xc2/0x270
 filename_symlinkat+0x295/0x2f0
 __x64_sys_symlinkat+0x62/0x90
 do_syscall_64+0x115/0x6a0
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Freed by task 661:
 kasan_save_stack+0x33/0x60
 kasan_save_track+0x14/0x30
 kasan_save_free_info+0x3b/0x60
 __kasan_slab_free+0x43/0x70
 kfree+0x2f9/0x530
 config_usb_cfg_unlink+0x173/0x1e0
 configfs_unlink+0x1fa/0x340
 vfs_unlink+0x15c/0x510
 filename_unlinkat+0x2ba/0x450
 __x64_sys_unlinkat+0x63/0x90
 do_syscall_64+0x115/0x6a0
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Fixes: c52661d60f63 ("usb-gadget: Initial merge of target module for UASP + BOT")
Cc: stable <stable@kernel.org>
Assisted-by: Codex:gpt-5.5
Signed-off-by: Cen Zhang <zzzccc427@gmail.com>
Link: https://patch.msgid.link/20260627104153.3822495-1-zzzccc427@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

2 files changed, 177 insertions, 28 deletions

diff --git a/drivers/usb/gadget/function/f_tcm.c b/drivers/usb/gadget/function/f_tcm.c
index 34d9f49e9987..b3fa5a17fd2d 100644
--- a/drivers/usb/gadget/function/f_tcm.c
+++ b/drivers/usb/gadget/function/f_tcm.c
@@ -2363,31 +2363,158 @@ ep_fail:
 	return -ENOTSUPP;
 }
 
-struct guas_setup_wq {
-	struct work_struct work;
-	struct f_uas *fu;
-	unsigned int alt;
-};
+static void tcm_cleanup_old_alt(struct f_uas *fu)
+{
+	if (fu->flags & USBG_IS_UAS)
+		uasp_cleanup_old_alt(fu);
+	else if (fu->flags & USBG_IS_BOT)
+		bot_cleanup_old_alt(fu);
+	fu->flags = 0;
+}
+
+static void tcm_delayed_set_alt_done(struct f_uas *fu)
+{
+	unsigned long flags;
+
+	spin_lock_irqsave(&fu->delayed_set_alt_lock, flags);
+	fu->delayed_set_alt_state = USBG_DELAYED_SET_ALT_IDLE;
+	fu->delayed_set_alt_cancel = false;
+	spin_unlock_irqrestore(&fu->delayed_set_alt_lock, flags);
+}
+
+static bool tcm_delayed_set_alt_cancelled(struct f_uas *fu)
+{
+	bool cancelled;
+	unsigned long flags;
+
+	spin_lock_irqsave(&fu->delayed_set_alt_lock, flags);
+	cancelled = fu->delayed_set_alt_cancel;
+	spin_unlock_irqrestore(&fu->delayed_set_alt_lock, flags);
+
+	return cancelled;
+}
+
+static bool tcm_complete_delayed_status(struct f_uas *fu)
+{
+	struct usb_composite_dev *cdev = fu->function.config->cdev;
+	struct usb_request *req = cdev->req;
+	unsigned long cdev_flags;
+	bool cancelled;
+	int ret;
+
+	spin_lock_irqsave(&cdev->lock, cdev_flags);
+	spin_lock(&fu->delayed_set_alt_lock);
+	cancelled = fu->delayed_set_alt_cancel;
+	if (!cancelled) {
+		fu->delayed_set_alt_state = USBG_DELAYED_SET_ALT_IDLE;
+		fu->delayed_set_alt_cancel = false;
+	}
+	spin_unlock(&fu->delayed_set_alt_lock);
+
+	if (cancelled) {
+		spin_unlock_irqrestore(&cdev->lock, cdev_flags);
+		return false;
+	}
+
+	if (cdev->delayed_status == 0) {
+		WARN(cdev, "%s: Unexpected call\n", __func__);
+	} else if (--cdev->delayed_status == 0) {
+		req->length = 0;
+		req->context = cdev;
+		ret = usb_ep_queue(cdev->gadget->ep0, req, GFP_ATOMIC);
+		if (ret == 0) {
+			cdev->setup_pending = true;
+		} else {
+			req->status = 0;
+			req->complete(cdev->gadget->ep0, req);
+		}
+	}
+
+	spin_unlock_irqrestore(&cdev->lock, cdev_flags);
+
+	return true;
+}
+
+static bool tcm_cancel_delayed_set_alt(struct f_uas *fu)
+{
+	bool cleanup = false;
+	bool cancel = false;
+	unsigned long flags;
+
+	spin_lock_irqsave(&fu->delayed_set_alt_lock, flags);
+	switch (fu->delayed_set_alt_state) {
+	case USBG_DELAYED_SET_ALT_IDLE:
+		cleanup = true;
+		break;
+	case USBG_DELAYED_SET_ALT_QUEUED:
+	case USBG_DELAYED_SET_ALT_RUNNING:
+		fu->delayed_set_alt_cancel = true;
+		cancel = true;
+		break;
+	}
+	spin_unlock_irqrestore(&fu->delayed_set_alt_lock, flags);
+
+	if (cancel && cancel_work(&fu->delayed_set_alt)) {
+		spin_lock_irqsave(&fu->delayed_set_alt_lock, flags);
+		if (fu->delayed_set_alt_state == USBG_DELAYED_SET_ALT_QUEUED) {
+			fu->delayed_set_alt_state = USBG_DELAYED_SET_ALT_IDLE;
+			fu->delayed_set_alt_cancel = false;
+			cleanup = true;
+		}
+		spin_unlock_irqrestore(&fu->delayed_set_alt_lock, flags);
+	}
+
+	return cleanup;
+}
+
+static void tcm_cancel_delayed_set_alt_sync(struct f_uas *fu)
+{
+	unsigned long flags;
+
+	spin_lock_irqsave(&fu->delayed_set_alt_lock, flags);
+	if (fu->delayed_set_alt_state != USBG_DELAYED_SET_ALT_IDLE)
+		fu->delayed_set_alt_cancel = true;
+	spin_unlock_irqrestore(&fu->delayed_set_alt_lock, flags);
+
+	cancel_work_sync(&fu->delayed_set_alt);
+
+	spin_lock_irqsave(&fu->delayed_set_alt_lock, flags);
+	fu->delayed_set_alt_state = USBG_DELAYED_SET_ALT_IDLE;
+	fu->delayed_set_alt_cancel = false;
+	spin_unlock_irqrestore(&fu->delayed_set_alt_lock, flags);
+}
 
 static void tcm_delayed_set_alt(struct work_struct *wq)
 {
-	struct guas_setup_wq *work = container_of(wq, struct guas_setup_wq,
-			work);
-	struct f_uas *fu = work->fu;
-	int alt = work->alt;
+	struct f_uas *fu = container_of(wq, struct f_uas, delayed_set_alt);
+	unsigned long flags;
+	unsigned int alt;
 
-	kfree(work);
+	spin_lock_irqsave(&fu->delayed_set_alt_lock, flags);
+	if (fu->delayed_set_alt_state != USBG_DELAYED_SET_ALT_QUEUED) {
+		spin_unlock_irqrestore(&fu->delayed_set_alt_lock, flags);
+		return;
+	}
+	fu->delayed_set_alt_state = USBG_DELAYED_SET_ALT_RUNNING;
+	alt = fu->delayed_alt;
+	spin_unlock_irqrestore(&fu->delayed_set_alt_lock, flags);
 
-	if (fu->flags & USBG_IS_BOT)
-		bot_cleanup_old_alt(fu);
-	if (fu->flags & USBG_IS_UAS)
-		uasp_cleanup_old_alt(fu);
+	tcm_cleanup_old_alt(fu);
+
+	if (tcm_delayed_set_alt_cancelled(fu))
+		goto out_done;
 
 	if (alt == USB_G_ALT_INT_BBB)
 		bot_set_alt(fu);
 	else if (alt == USB_G_ALT_INT_UAS)
 		uasp_set_alt(fu);
-	usb_composite_setup_continue(fu->function.config->cdev);
+
+	if (tcm_complete_delayed_status(fu))
+		return;
+
+	tcm_cleanup_old_alt(fu);
+out_done:
+	tcm_delayed_set_alt_done(fu);
 }
 
 static int tcm_get_alt(struct usb_function *f, unsigned intf)
@@ -2413,15 +2540,20 @@ static int tcm_set_alt(struct usb_function *f, unsigned intf, unsigned alt)
 		return -EOPNOTSUPP;
 
 	if ((alt == USB_G_ALT_INT_BBB) || (alt == USB_G_ALT_INT_UAS)) {
-		struct guas_setup_wq *work;
+		unsigned long flags;
 
-		work = kmalloc_obj(*work, GFP_ATOMIC);
-		if (!work)
-			return -ENOMEM;
-		INIT_WORK(&work->work, tcm_delayed_set_alt);
-		work->fu = fu;
-		work->alt = alt;
-		schedule_work(&work->work);
+		spin_lock_irqsave(&fu->delayed_set_alt_lock, flags);
+		if (fu->delayed_set_alt_state != USBG_DELAYED_SET_ALT_IDLE) {
+			spin_unlock_irqrestore(&fu->delayed_set_alt_lock,
+					       flags);
+			return -EBUSY;
+		}
+		fu->delayed_alt = alt;
+		fu->delayed_set_alt_cancel = false;
+		fu->delayed_set_alt_state = USBG_DELAYED_SET_ALT_QUEUED;
+		spin_unlock_irqrestore(&fu->delayed_set_alt_lock, flags);
+
+		schedule_work(&fu->delayed_set_alt);
 		return USB_GADGET_DELAYED_STATUS;
 	}
 	return -EOPNOTSUPP;
@@ -2431,11 +2563,8 @@ static void tcm_disable(struct usb_function *f)
 {
 	struct f_uas *fu = to_f_uas(f);
 
-	if (fu->flags & USBG_IS_UAS)
-		uasp_cleanup_old_alt(fu);
-	else if (fu->flags & USBG_IS_BOT)
-		bot_cleanup_old_alt(fu);
-	fu->flags = 0;
+	if (tcm_cancel_delayed_set_alt(fu))
+		tcm_cleanup_old_alt(fu);
 }
 
 static int tcm_setup(struct usb_function *f,
@@ -2583,11 +2712,16 @@ static void tcm_free(struct usb_function *f)
 {
 	struct f_uas *tcm = to_f_uas(f);
 
+	tcm_cancel_delayed_set_alt_sync(tcm);
 	kfree(tcm);
 }
 
 static void tcm_unbind(struct usb_configuration *c, struct usb_function *f)
 {
+	struct f_uas *fu = to_f_uas(f);
+
+	tcm_cancel_delayed_set_alt_sync(fu);
+	tcm_cleanup_old_alt(fu);
 	usb_free_all_descriptors(f);
 }
 
@@ -2620,6 +2754,8 @@ static struct usb_function *tcm_alloc(struct usb_function_instance *fi)
 	fu->function.disable = tcm_disable;
 	fu->function.free_func = tcm_free;
 	fu->tpg = tpg_instances[i].tpg;
+	INIT_WORK(&fu->delayed_set_alt, tcm_delayed_set_alt);
+	spin_lock_init(&fu->delayed_set_alt_lock);
 
 	hash_init(fu->stream_hash);
 	mutex_unlock(&tpg_instances_lock);
diff --git a/drivers/usb/gadget/function/tcm.h b/drivers/usb/gadget/function/tcm.h
index 009974d81d66..e1d5a9391612 100644
--- a/drivers/usb/gadget/function/tcm.h
+++ b/drivers/usb/gadget/function/tcm.h
@@ -3,6 +3,7 @@
 #define __TARGET_USB_GADGET_H__
 
 #include <linux/kref.h>
+#include <linux/spinlock.h>
 /* #include <linux/usb/uas.h> */
 #include <linux/hashtable.h>
 #include <linux/usb/composite.h>
@@ -29,6 +30,12 @@ enum {
 
 #define USB_G_DEFAULT_SESSION_TAGS	USBG_NUM_CMDS
 
+enum {
+	USBG_DELAYED_SET_ALT_IDLE = 0,
+	USBG_DELAYED_SET_ALT_QUEUED,
+	USBG_DELAYED_SET_ALT_RUNNING,
+};
+
 struct tcm_usbg_nexus {
 	struct se_session *tvn_se_sess;
 };
@@ -132,6 +139,12 @@ struct f_uas {
 #define USBG_BOT_CMD_PEND	(1 << 4)
 #define USBG_BOT_WEDGED		(1 << 5)
 
+	struct work_struct	delayed_set_alt;
+	spinlock_t		delayed_set_alt_lock; /* protects delayed_set_alt_* */
+	unsigned int		delayed_alt;
+	unsigned int		delayed_set_alt_state;
+	bool			delayed_set_alt_cancel;
+
 	struct usbg_cdb		cmd[USBG_NUM_CMDS];
 	struct usb_ep		*ep_in;
 	struct usb_ep		*ep_out;