linux-kernel - [PATCH 0/1] Fix race condition causing NULL pointer dereference

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Message-ID: <20250301081057.1952519-1-akuchynski@chromium.org>
Date: Sat,  1 Mar 2025 08:10:55 +0000
From: Andrei Kuchynski <akuchynski@...omium.org>
To: Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
	Benson Leung <bleung@...omium.org>,
	"Christian A. Ehrhardt" <lk@...e.de>,
	Jameson Thies <jthies@...gle.com>,
	linux-usb@...r.kernel.org,
	linux-kernel@...r.kernel.org
Cc: Andrei Kuchynski <akuchynski@...omium.org>
Subject: [PATCH 0/1] Fix race condition causing NULL pointer dereference

The kernel crashes during UCSI initialization due to a race condition.
In ucsi_init():
1. ucsi_register_port() sets up a work queue and schedules
ucsi_check_connector_capability task.
2. "PPM policy conflict" causes ucsi_send_command to fail.
3. The error path (err_unregister) deallocates resources,
setting con->partner to NULL.
4. After that, ucsi_init() waits for the work queue to finish its task.
5. ucsi_check_connector_capability task, running in the work queue,
attempts to dereference the con->partner pointer, resulting in the crash.

The core issue is that con->partner is set to NULL before
the work queue task is guaranteed to have finished using it.

The crash log:

cros_ec_ucsi cros_ec_ucsi.3.auto: PPM Policy conflict
 BUG: kernel NULL pointer dereference, address: 000000000000030c
 #PF: supervisor read access in kernel mode
 #PF: error_code(0x0000) - not-present page
 PGD 0 P4D 0Oops: Oops: 0000 [#1] PREEMPT SMP NOPTI
 CPU: 8 UID: 0 PID: 13 Comm: kworker/u64:1 Tainted: G     U  W          
 6.12.0-g15b373ee5573-dirty #1 b5276ebf6ba85f471d9524ce34509877165c9f58
 Tainted: [U]=USER, [W]=WARN
 Hardware name: Google Fatcat/Fatcat, BIOS Google_Fatcat.16163.0.0 01/15/2025
 Workqueue: cros_ec_ucsi.3.auto-con1 ucsi_poll_worker [typec_ucsi]
 RIP: 0010:typec_partner_set_pd_revision+0x5/0x80 [typec]
 Code: cc cc cc b8 ea ff ff ff c3 cc cc cc cc cc 0f 1f 80 00 00 00 00 90 90 90
 90 90 90 90 90 90 90 90 90 90 90 90 90 0f 1f 44 00 00 <66> 39 b7 0c 03 00 00
 75 06 c3 cc cc cc cc cc 55 48 89 e5 41 56 53
 RSP: 0018:ffffb532400c7dd8 EFLAGS: 00010206
 RAX: 0000000000000004 RBX: 0000000000000004 RCX: 0000000000000000
 RDX: ffffb532400c7cc0 RSI: 0000000000000300 RDI: 0000000000000000
 RBP: ffffb532400c7de8 R08: ffffa3ab042d28f0 R09: 0000000000000080
 R10: 0000000000000080 R11: 00000000000000c0 R12: ffffa3ab01dc6480
 R13: ffffa3ab120d12c0 R14: ffffa3ab120d12c0 R15: ffffa3ab12074000
 FS:  0000000000000000(0000) GS:ffffa3ae6f800000(0000) knlGS:0000000000000000
 CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
 CR2: 000000000000030c CR3: 000000010700e004 CR4: 0000000000772ef0
 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
 DR3: 0000000000000000 DR6: 00000000ffff07f0 DR7: 0000000000000400
 PKRU: 55555554
 Call Trace:
  <TASK>
  ? __die_body+0x6a/0xb0
  ? page_fault_oops+0x38e/0x400
  ? work_grab_pending+0x56/0x230
  ? exc_page_fault+0x5b/0xb0
  ? asm_exc_page_fault+0x22/0x30
  ? typec_partner_set_pd_revision+0x5/0x80 
  [typec bc1e7c7e089f4aaed440a0a5388387e3ef1ca2cb]
  ucsi_check_connector_capability+0x71/0xa0 \
  [typec_ucsi 843b0396f746abb17c01f8d4d12ead8b09b88609]
  ucsi_poll_worker+0x3c/0x110 
  [typec_ucsi 843b0396f746abb17c01f8d4d12ead8b09b88609]
  process_scheduled_works+0x20e/0x450
  worker_thread+0x2e0/0x390
  kthread+0xee/0x110
  ? __pfx_worker_thread+0x10/0x10
  ? __pfx_kthread+0x10/0x10
  ret_from_fork+0x38/0x50
  ? __pfx_kthread+0x10/0x10
  ret_from_fork_asm+0x1a/0x30
  </TASK>

Andrei Kuchynski (1):
  usb: typec: ucsi: Fix NULL pointer access

 drivers/usb/typec/ucsi/ucsi.c | 13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

-- 
2.48.1.711.g2feabab25a-goog