Subject: CVE-2024-43900: media: xc2028: avoid use-after-free in load_firmware_cb()

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

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

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.

[1]:
    ==================================================================
     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.

The Linux kernel CVE team has assigned CVE-2024-43900 to this issue.

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

	Fixed in 6.1.105 with commit ef517bdfc018
	Fixed in 6.6.46 with commit 850304152d36
	Fixed in 6.10.5 with commit 208deb6d8c3c
	Fixed in 6.11 with commit 68594cec291f

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-2024-43900
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/media/tuners/xc2028.c

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/ef517bdfc01818419f7bd426969a0c86b14f3e0e
	https://git.kernel.org/stable/c/850304152d367f104d21c77cfbcc05806504218b
	https://git.kernel.org/stable/c/208deb6d8c3cb8c3acb1f41eb31cf68ea08726d5
	https://git.kernel.org/stable/c/68594cec291ff9523b9feb3f43fd853dcddd1f60