usb: gadget: f_tcm: synchronize delayed set_alt with teardown

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>