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Message-ID: <0f358cc9-c8cf-4fd9-80d5-b524cc5b6c3c@kernel.org>
Date: Wed, 10 Sep 2025 17:07:29 +0200
From: Hans de Goede <hansg@...nel.org>
To: Janne Grunau <j@...nau.net>, Helge Deller <deller@....de>,
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 v2] fbdev/simplefb: Fix use after free in
simplefb_detach_genpds()
Hi Janne,
On 8-Sep-25 11:23 PM, 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.
Thank you for your patch.
This patch seems to miss adding a simplefb_detach_genpds()
on error-exit from simplefb_probe() after a successful
simplefb_attach_genpds() call ?
Regards,
Hans
>
> [ 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 v2:
> - reworked change due to missed use of `par->num_genpds` before setting
> it. Missed in testing due to FB_SIMPLE vs. SYSFB_SIMPLEFB.
> - Link to v1: https://lore.kernel.org/r/20250901-simplefb-genpd-uaf-v1-1-0d9f3a34c4dc@jannau.net
> ---
> drivers/video/fbdev/simplefb.c | 22 ++++++++++++++++------
> 1 file changed, 16 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/video/fbdev/simplefb.c b/drivers/video/fbdev/simplefb.c
> index 1893815dc67f4c1403eea42c0e10a7ead4d96ba9..2f3e5449509d1824a3d26f73e103af82d56d558a 100644
> --- a/drivers/video/fbdev/simplefb.c
> +++ b/drivers/video/fbdev/simplefb.c
> @@ -93,6 +93,7 @@ struct simplefb_par {
>
> static void simplefb_clocks_destroy(struct simplefb_par *par);
> static void simplefb_regulators_destroy(struct simplefb_par *par);
> +static void simplefb_detach_genpds(void *res);
>
> /*
> * fb_ops.fb_destroy is called by the last put_fb_info() call at the end
> @@ -105,6 +106,7 @@ static void simplefb_destroy(struct fb_info *info)
>
> simplefb_regulators_destroy(info->par);
> simplefb_clocks_destroy(info->par);
> + simplefb_detach_genpds(info->par);
> if (info->screen_base)
> iounmap(info->screen_base);
>
> @@ -451,7 +453,7 @@ static int simplefb_attach_genpds(struct simplefb_par *par,
> struct platform_device *pdev)
> {
> struct device *dev = &pdev->dev;
> - unsigned int i;
> + unsigned int i, num_genpds;
> int err;
>
> err = of_count_phandle_with_args(dev->of_node, "power-domains",
> @@ -465,26 +467,33 @@ static int simplefb_attach_genpds(struct simplefb_par *par,
> return err;
> }
>
> - par->num_genpds = err;
> + num_genpds = err;
>
> /*
> * Single power-domain devices are handled by the driver core, so
> * nothing to do here.
> */
> - if (par->num_genpds <= 1)
> + if (num_genpds <= 1)
> return 0;
>
> - par->genpds = devm_kcalloc(dev, par->num_genpds, sizeof(*par->genpds),
> + par->genpds = devm_kcalloc(dev, num_genpds, sizeof(*par->genpds),
> GFP_KERNEL);
> if (!par->genpds)
> return -ENOMEM;
>
> - par->genpd_links = devm_kcalloc(dev, par->num_genpds,
> + par->genpd_links = devm_kcalloc(dev, num_genpds,
> sizeof(*par->genpd_links),
> GFP_KERNEL);
> if (!par->genpd_links)
> return -ENOMEM;
>
> + /*
> + * Set par->num_genpds only after genpds and genpd_links are allocated
> + * to exit early from simplefb_detach_genpds() without full
> + * initialisation.
> + */
> + par->num_genpds = num_genpds;
> +
> for (i = 0; i < par->num_genpds; i++) {
> par->genpds[i] = dev_pm_domain_attach_by_id(dev, i);
> if (IS_ERR(par->genpds[i])) {
> @@ -506,9 +515,10 @@ static int simplefb_attach_genpds(struct simplefb_par *par,
> dev_warn(dev, "failed to link power-domain %u\n", i);
> }
>
> - return devm_add_action_or_reset(dev, simplefb_detach_genpds, par);
> + return 0;
> }
> #else
> +static void simplefb_detach_genpds(void *res) { }
> static int simplefb_attach_genpds(struct simplefb_par *par,
> struct platform_device *pdev)
> {
>
> ---
> base-commit: 8f5ae30d69d7543eee0d70083daf4de8fe15d585
> change-id: 20250901-simplefb-genpd-uaf-352704761a29
>
> Best regards,
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