CVE-2026-98694

In the Linux kernel, the following vulnerability has been resolved:

thunderbolt: Fix KASAN reported use-after-free when request is canceled

Alan reported that when doing stress testing sometimes KASAN notices
use-after-free during control channel operation (stripped down keeping
the relevant parts):

 BUG: KASAN: slab-use-after-free in tb_cfg_request_sync+0x240/0x250 [thunderbolt]
 Read of size 24 at addr ffff88811067f290 by task kworker/u40:2/1760
  <TASK>
  tb_cfg_request_sync+0x240/0x250 [thunderbolt]
  tb_cfg_read_raw+0x367/0x510 [thunderbolt]
  tb_cfg_read+0xec/0x240 [thunderbolt]
  tb_port_get_link_generation+0x258/0x420 [thunderbolt]
  tb_usb3_consumed_bandwidth+0x1c1/0x2c0 [thunderbolt]
  tb_tunnel_consumed_bandwidth+0xfd/0x910 [thunderbolt]
  tb_available_bandwidth+0x5f2/0xeb0 [thunderbolt]
  tb_recalc_estimated_bandwidth+0x2a0/0x1bc0 [thunderbolt]
  tb_handle_dp_bandwidth_request+0x1897/0x5e20 [thunderbolt]
  process_one_work+0x675/0x1230
  worker_thread+0x5e6/0xf70
  kthread+0x365/0x470
  ret_from_fork+0x54d/0x710
  ret_from_fork_asm+0x1a/0x30
  </TASK>

 Allocated by task 1760:
  __kmalloc_cache_noprof+0x1ee/0x550
  tb_cfg_read_raw+0x1d3/0x510 [thunderbolt]
  tb_cfg_read+0xec/0x240 [thunderbolt]
  tb_port_get_link_generation+0x258/0x420 [thunderbolt]
  tb_usb3_consumed_bandwidth+0x1c1/0x2c0 [thunderbolt]
  tb_tunnel_consumed_bandwidth+0xfd/0x910 [thunderbolt]
  tb_available_bandwidth+0x5f2/0xeb0 [thunderbolt]
  tb_recalc_estimated_bandwidth+0x2a0/0x1bc0 [thunderbolt]
  tb_handle_dp_bandwidth_request+0x1897/0x5e20 [thunderbolt]
  process_one_work+0x675/0x1230
  worker_thread+0x5e6/0xf70
  kthread+0x365/0x470
  ret_from_fork+0x54d/0x710
  ret_from_fork_asm+0x1a/0x30

 Freed by task 926:
  kfree+0x18f/0x4a0
  tb_cfg_request_put+0xb7/0xe0 [thunderbolt]
  tb_cfg_request_work+0x82/0x120 [thunderbolt]
  process_one_work+0x675/0x1230
  worker_thread+0x5e6/0xf70
  kthread+0x365/0x470
  ret_from_fork+0x54d/0x710
  ret_from_fork_asm+0x1a/0x30

 Second to last potentially related work creation:
  __queue_work+0x575/0xd00
  queue_work_on+0x77/0x80
  tb_cfg_request_cancel+0xc7/0x260 [thunderbolt]
  tb_cfg_request_sync+0x1f6/0x250 [thunderbolt]
  tb_cfg_read_raw+0x367/0x510 [thunderbolt]
  tb_cfg_read+0xec/0x240 [thunderbolt]
  tb_port_get_link_generation+0x258/0x420 [thunderbolt]
  tb_usb3_consumed_bandwidth+0x1c1/0x2c0 [thunderbolt]
  tb_tunnel_consumed_bandwidth+0xfd/0x910 [thunderbolt]
  tb_available_bandwidth+0x5f2/0xeb0 [thunderbolt]
  tb_recalc_estimated_bandwidth+0x2a0/0x1bc0 [thunderbolt]
  tb_handle_dp_bandwidth_request+0x1897/0x5e20 [thunderbolt]
  process_one_work+0x675/0x1230
  worker_thread+0x5e6/0xf70
  kthread+0x365/0x470
  ret_from_fork+0x54d/0x710
  ret_from_fork_asm+0x1a/0x30

The last stack trace is helpful because it shows that we are cancelling
a request and looking at tb_cfg_request_cancel() what might happen is
that tb_cfg_request_work() completes right before tb_cfg_request_cancel()
starts and because of this it will call schedule_work() queueing the
same work to run again. However, it is already removed from the
request_queue and reference count is dropped so when
tb_cfg_request_work() triggers again it will access memory that is
already released.

Fix this so that we first make sure a cancelled request is not handed
away from tb_cfg_request_find() or scheduled to run. Then instead of
relying on the worker to clean up the request we will do it in
tb_cfg_request_cancel() after the work is canceled from running. Make
tb_cfg_request_dequeue() release the request only if it was actually
removed from the queue.