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Message-ID: <20251001061102.GA1519657@robin.jannau.net>
Date: Wed, 1 Oct 2025 08:11:02 +0200
From: Janne Grunau <j@...nau.net>
To: Helge Deller <deller@....de>
Cc: Hans de Goede <hansg@...nel.org>, Thierry Reding <treding@...dia.com>,
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 Tue, Sep 30, 2025 at 09:12:21PM +0200, Helge Deller wrote:
> 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.
>
> PS: Janne, if you want to push yourself via drm-misc, just let me know and I drop it...
I won't. My request for commit access is still pending. I should fine
someone at xdc to ask about that.
Janne
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