linux-kernel - [PATCH v2] [media] em28xx-input: fix refcount bug in em28xx_usb

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Date:   Wed,  7 Jul 2021 17:34:09 +0800
From:   Dongliang Mu <mudongliangabcd@...il.com>
To:     Mauro Carvalho Chehab <mchehab@...nel.org>,
        Igor Matheus Andrade Torrente <igormtorrente@...il.com>,
        Hans Verkuil <hverkuil-cisco@...all.nl>
Cc:     Dongliang Mu <mudongliangabcd@...il.com>,
        Mauro Carvalho Chehab <mchehab+huawei@...nel.org>,
        linux-media@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH v2] [media] em28xx-input: fix refcount bug in em28xx_usb_disconnect

If em28xx_ir_init fails, it would decrease the refcount of dev. However,
in the em28xx_ir_fini, when ir is NULL, it goes to ref_put and decrease
the refcount of dev. This will lead to a refcount bug.

Fix this bug by removing the kref_put in the error handling code
of em28xx_ir_init.

refcount_t: underflow; use-after-free.
WARNING: CPU: 0 PID: 7 at lib/refcount.c:28 refcount_warn_saturate+0x18e/0x1a0 lib/refcount.c:28
Modules linked in:
CPU: 0 PID: 7 Comm: kworker/0:1 Not tainted 5.13.0 #3
Workqueue: usb_hub_wq hub_event
RIP: 0010:refcount_warn_saturate+0x18e/0x1a0 lib/refcount.c:28
Call Trace:
  kref_put.constprop.0+0x60/0x85 include/linux/kref.h:69
  em28xx_usb_disconnect.cold+0xd7/0xdc drivers/media/usb/em28xx/em28xx-cards.c:4150
  usb_unbind_interface+0xbf/0x3a0 drivers/usb/core/driver.c:458
  __device_release_driver drivers/base/dd.c:1201 [inline]
  device_release_driver_internal+0x22a/0x230 drivers/base/dd.c:1232
  bus_remove_device+0x108/0x160 drivers/base/bus.c:529
  device_del+0x1fe/0x510 drivers/base/core.c:3540
  usb_disable_device+0xd1/0x1d0 drivers/usb/core/message.c:1419
  usb_disconnect+0x109/0x330 drivers/usb/core/hub.c:2221
  hub_port_connect drivers/usb/core/hub.c:5151 [inline]
  hub_port_connect_change drivers/usb/core/hub.c:5440 [inline]
  port_event drivers/usb/core/hub.c:5586 [inline]
  hub_event+0xf81/0x1d40 drivers/usb/core/hub.c:5668
  process_one_work+0x2c9/0x610 kernel/workqueue.c:2276
  process_scheduled_works kernel/workqueue.c:2338 [inline]
  worker_thread+0x333/0x5b0 kernel/workqueue.c:2424
  kthread+0x188/0x1d0 kernel/kthread.c:319
  ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295

Reported-by: Dongliang Mu <mudongliangabcd@...il.com>
Fixes: ac5688637144 ("media: em28xx: Fix possible memory leak of em28xx struct")
Signed-off-by: Dongliang Mu <mudongliangabcd@...il.com>
---
v1->v2: move kref_get to the original position
 drivers/media/usb/em28xx/em28xx-input.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/drivers/media/usb/em28xx/em28xx-input.c b/drivers/media/usb/em28xx/em28xx-input.c
index 59529cbf9cd0..0b6d77c3bec8 100644
--- a/drivers/media/usb/em28xx/em28xx-input.c
+++ b/drivers/media/usb/em28xx/em28xx-input.c
@@ -842,7 +842,6 @@ static int em28xx_ir_init(struct em28xx *dev)
 	kfree(ir);
 ref_put:
 	em28xx_shutdown_buttons(dev);
-	kref_put(&dev->ref, em28xx_free_device);
 	return err;
 }

-- 
2.25.1