fbdev: simplefb: Fix use after free in simplefb_detach_genpds()
CVE: CVE-2025-40037
Component: kernel
CWE: CWE-416
Severity: Moderate
CVSS v3: 5.6/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
Release date: 2025-10-28T00:00:00+00:00

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

fbdev: simplefb: Fix use after free in simplefb_detach_genpds()

The pm_domain cleanup can not be devres managed as it uses struct
simplefb_par which is allocated within struct fb_info by
framebuffer_alloc(). This allocation is explicitly freed by
unregister_framebuffer() in simplefb_remove().
Devres managed cleanup runs after the device remove call and thus can no
longer access struct simplefb_par.
Call simplefb_detach_genpds() explicitly from simplefb_destroy() like
the cleanup functions for clocks and regulators.

Fixes an use after free on M2 Mac mini during
aperture_remove_conflicting_devices() using the downstream asahi kernel
with Debian's kernel config. For unknown reasons this started to
consistently dereference an invalid pointer in v6.16.3 based kernels.

[    6.736134] BUG: KASAN: slab-use-after-free in simplefb_detach_genpds+0x58/0x220
[    6.743545] Read of size 4 at addr ffff8000304743f0 by task (udev-worker)/227
[    6.750697]
[    6.752182] CPU: 6 UID: 0 PID: 227 Comm: (udev-worker) Tainted: G S                  6.16.3-asahi+ #16 PREEMPTLAZY
[    6.752186] Tainted: [S]=CPU_OUT_OF_SPEC
[    6.752187] Hardware name: Apple Mac mini (M2, 2023) (DT)
[    6.752189] Call trace:
[    6.752190]  show_stack+0x34/0x98 (C)
[    6.752194]  dump_stack_lvl+0x60/0x80
[    6.752197]  print_report+0x17c/0x4d8
[    6.752201]  kasan_report+0xb4/0x100
[    6.752206]  __asan_report_load4_noabort+0x20/0x30
[    6.752209]  simplefb_detach_genpds+0x58/0x220
[    6.752213]  devm_action_release+0x50/0x98
[    6.752216]  release_nodes+0xd0/0x2c8
[    6.752219]  devres_release_all+0xfc/0x178
[    6.752221]  device_unbind_cleanup+0x28/0x168
[    6.752224]  device_release_driver_internal+0x34c/0x470
[    6.752228]  device_release_driver+0x20/0x38
[    6.752231]  bus_remove_device+0x1b0/0x380
[    6.752234]  device_del+0x314/0x820
[    6.752238]  platform_device_del+0x3c/0x1e8
[    6.752242]  platform_device_unregister+0x20/0x50
[    6.752246]  aperture_detach_platform_device+0x1c/0x30
[    6.752250]  aperture_detach_devices+0x16c/0x290
[    6.752253]  aperture_remove_conflicting_devices+0x34/0x50
...
[    6.752343]
[    6.967409] Allocated by task 62:
[    6.970724]  kasan_save_stack+0x3c/0x70
[    6.974560]  kasan_save_track+0x20/0x40
[    6.978397]  kasan_save_alloc_info+0x40/0x58
[    6.982670]  __kasan_kmalloc+0xd4/0xd8
[    6.986420]  __kmalloc_noprof+0x194/0x540
[    6.990432]  framebuffer_alloc+0xc8/0x130
[    6.994444]  simplefb_probe+0x258/0x2378
...
[    7.054356]
[    7.055838] Freed by task 227:
[    7.058891]  kasan_save_stack+0x3c/0x70
[    7.062727]  kasan_save_track+0x20/0x40
[    7.066565]  kasan_save_free_info+0x4c/0x80
[    7.070751]  __kasan_slab_free+0x6c/0xa0
[    7.074675]  kfree+0x10c/0x380
[    7.077727]  framebuffer_release+0x5c/0x90
[    7.081826]  simplefb_destroy+0x1b4/0x2c0
[    7.085837]  put_fb_info+0x98/0x100
[    7.089326]  unregister_framebuffer+0x178/0x320
[    7.093861]  simplefb_remove+0x3c/0x60
[    7.097611]  platform_remove+0x60/0x98
[    7.101361]  device_remove+0xb8/0x160
[    7.105024]  device_release_driver_internal+0x2fc/0x470
[    7.110256]  device_release_driver+0x20/0x38
[    7.114529]  bus_remove_device+0x1b0/0x380
[    7.118628]  device_del+0x314/0x820
[    7.122116]  platform_device_del+0x3c/0x1e8
[    7.126302]  platform_device_unregister+0x20/0x50
[    7.131012]  aperture_detach_platform_device+0x1c/0x30
[    7.136157]  aperture_detach_devices+0x16c/0x290
[    7.140779]  aperture_remove_conflicting_devices+0x34/0x50
...

Statement: The fix removes devres-managed cleanup for power domains and calls simplefb_detach_genpds() explicitly from simplefb_destroy(), aligning PD teardown with clocks/regulators and ensuring it runs before fb_info/simplefb_par is freed. par->num_genpds is set only after successful allocations and reset to 0 during detach to prevent double-free or use after free. Error paths in probe() now call simplefb_detach_genpds(par) explicitly.

Remediation: