CVE-2026-68367: usb: gadget: f_tcm: synchronize delayed set_alt with teardown

From: Greg Kroah-Hartman <[email protected]>

Description
===========

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

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

The Linux kernel CVE team has assigned CVE-2026-68367 to this issue.


Affected and fixed versions
===========================

	Issue introduced in 3.5 with commit c52661d60f636d17e26ad834457db333bd1df494 and fixed in 6.6.151 with commit 3118bb872c7dff653294f193d5328a476619e04d
	Issue introduced in 3.5 with commit c52661d60f636d17e26ad834457db333bd1df494 and fixed in 6.12.103 with commit a6eb5a0ae7cd313cfd7df78decd8f43b64c68703
	Issue introduced in 3.5 with commit c52661d60f636d17e26ad834457db333bd1df494 and fixed in 6.18.42 with commit f282242906c12fd476b86757afba51f211d4f959
	Issue introduced in 3.5 with commit c52661d60f636d17e26ad834457db333bd1df494 and fixed in 7.1.6 with commit 4c6c6a5588b9a2f8437fb794e852d05fa60ebe53
	Issue introduced in 3.5 with commit c52661d60f636d17e26ad834457db333bd1df494 and fixed in 7.2-rc5 with commit 79e2d75725c85607f8a9d87ae9cace62a19f767d

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2026-68367
will be updated if fixes are backported, please check that for the most
up to date information about this issue.


Affected files
==============

The file(s) affected by this issue are:
	drivers/usb/gadget/function/f_tcm.c
	drivers/usb/gadget/function/tcm.h


Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/3118bb872c7dff653294f193d5328a476619e04d
	https://git.kernel.org/stable/c/a6eb5a0ae7cd313cfd7df78decd8f43b64c68703
	https://git.kernel.org/stable/c/f282242906c12fd476b86757afba51f211d4f959
	https://git.kernel.org/stable/c/4c6c6a5588b9a2f8437fb794e852d05fa60ebe53
	https://git.kernel.org/stable/c/79e2d75725c85607f8a9d87ae9cace62a19f767d