linux-kernel - Re: [PATCH v3] fbdev/simplefb: Fix use after free in simplefb_detach

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Message-ID: <e0b113e6-8b3d-4d2d-b1b8-cd6609b8bca7@gmx.de>
Date: Tue, 30 Sep 2025 21:12:21 +0200
From: Helge Deller <deller@....de>
To: Janne Grunau <j@...nau.net>, Hans de Goede <hansg@...nel.org>,
 Thierry Reding <treding@...dia.com>
Cc: linux-fbdev@...r.kernel.org, dri-devel@...ts.freedesktop.org,
 linux-kernel@...r.kernel.org, Daniel Huhardeaux <tech@...tai.net>,
 stable@...r.kernel.org
Subject: Re: [PATCH v3] fbdev/simplefb: Fix use after free in
 simplefb_detach_genpds()

On 9/15/25 08:36, Janne Grunau wrote:
> 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
> ...
> 
> Reported-by: Daniel Huhardeaux <tech@...tai.net>
> Cc: stable@...r.kernel.org
> Fixes: 92a511a568e44 ("fbdev/simplefb: Add support for generic power-domains")
> Signed-off-by: Janne Grunau <j@...nau.net>
> ---
> Changes in v3:
> - release power-domains on probe errors
> - set par->num_genpds when it's <= 1
> - set par->num_genpds to 0 after detaching
> - Link to v2: https://lore.kernel.org/r/20250908-simplefb-genpd-uaf-v2-1-f88a0d9d880f@jannau.net
> 
> Changes in v2:
> - reworked change due to missed use of `par->num_genpds` before setting
>    it. Missed in testing due to mixing up FB_SIMPLE and SYSFB_SIMPLEFB.
> - Link to v1: https://lore.kernel.org/r/20250901-simplefb-genpd-uaf-v1-1-0d9f3a34c4dc@jannau.net
> ---
>   drivers/video/fbdev/simplefb.c | 31 +++++++++++++++++++++++--------
>   1 file changed, 23 insertions(+), 8 deletions(-)

applied to fbdev git tree.
Thanks!
Helge

PS: Janne, if you want to push yourself via drm-misc, just let me know and I drop it...