CVE-2024-43900

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

media: xc2028: avoid use-after-free in load_firmware_cb()

syzkaller reported use-after-free in load_firmware_cb() 1.
The reason is because the module allocated a struct tuner in tuner_probe(),
and then the module initialization failed, the struct tuner was released.
A worker which created during module initialization accesses this struct
tuner later, it caused use-after-free.

The process is as follows:

task-6504 worker_thread
tuner_probe <= alloc dvb_frontend [2]
…
request_firmware_nowait <= create a worker
…
tuner_remove <= free dvb_frontend
…
request_firmware_work_func <= the firmware is ready
load_firmware_cb <= but now the dvb_frontend has been freed

To fix the issue, check the dvd_frontend in load_firmware_cb(), if it is
null, report a warning and just return.

 BUG: KASAN: use-after-free in load_firmware_cb+0x1310/0x17a0
 Read of size 8 at addr ffff8000d7ca2308 by task kworker/2:3/6504

 Call trace:
  load_firmware_cb+0x1310/0x17a0
  request_firmware_work_func+0x128/0x220
  process_one_work+0x770/0x1824
  worker_thread+0x488/0xea0
  kthread+0x300/0x430
  ret_from_fork+0x10/0x20

 Allocated by task 6504:
  kzalloc
  tuner_probe+0xb0/0x1430
  i2c_device_probe+0x92c/0xaf0
  really_probe+0x678/0xcd0
  driver_probe_device+0x280/0x370
  __device_attach_driver+0x220/0x330
  bus_for_each_drv+0x134/0x1c0
  __device_attach+0x1f4/0x410
  device_initial_probe+0x20/0x30
  bus_probe_device+0x184/0x200
  device_add+0x924/0x12c0
  device_register+0x24/0x30
  i2c_new_device+0x4e0/0xc44
  v4l2_i2c_new_subdev_board+0xbc/0x290
  v4l2_i2c_new_subdev+0xc8/0x104
  em28xx_v4l2_init+0x1dd0/0x3770

 Freed by task 6504:
  kfree+0x238/0x4e4
  tuner_remove+0x144/0x1c0
  i2c_device_remove+0xc8/0x290
  __device_release_driver+0x314/0x5fc
  device_release_driver+0x30/0x44
  bus_remove_device+0x244/0x490
  device_del+0x350/0x900
  device_unregister+0x28/0xd0
  i2c_unregister_device+0x174/0x1d0
  v4l2_device_unregister+0x224/0x380
  em28xx_v4l2_init+0x1d90/0x3770

 The buggy address belongs to the object at ffff8000d7ca2000
  which belongs to the cache kmalloc-2k of size 2048
 The buggy address is located 776 bytes inside of
  2048-byte region [ffff8000d7ca2000, ffff8000d7ca2800)
 The buggy address belongs to the page:
 page:ffff7fe00035f280 count:1 mapcount:0 mapping:ffff8000c001f000 index:0x0
 flags: 0x7ff800000000100(slab)
 raw: 07ff800000000100 ffff7fe00049d880 0000000300000003 ffff8000c001f000
 raw: 0000000000000000 0000000080100010 00000001ffffffff 0000000000000000
 page dumped because: kasan: bad access detected

 Memory state around the buggy address:
  ffff8000d7ca2200: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
  ffff8000d7ca2280: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 >ffff8000d7ca2300: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                       ^
  ffff8000d7ca2380: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
  ffff8000d7ca2400: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ==================================================================

[2]
Actually, it is allocated for struct tuner, and dvb_frontend is inside.