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Message-Id: <20250901-simplefb-genpd-uaf-v1-1-0d9f3a34c4dc@jannau.net>
Date: Mon, 01 Sep 2025 11:12:45 +0200
From: Janne Grunau <j@...nau.net>
To: Hans de Goede <hansg@...nel.org>, 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, Janne Grunau <j@...nau.net>
Subject: [PATCH] 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
...
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>
---
drivers/video/fbdev/simplefb.c | 15 +++++++++++----
1 file changed, 11 insertions(+), 4 deletions(-)
diff --git a/drivers/video/fbdev/simplefb.c b/drivers/video/fbdev/simplefb.c
index 1893815dc67f4c1403eea42c0e10a7ead4d96ba9..cd5193e704ffe1ccc178c13916a462446af9cb14 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);
@@ -465,13 +467,11 @@ static int simplefb_attach_genpds(struct simplefb_par *par,
return err;
}
- par->num_genpds = err;
-
/*
* Single power-domain devices are handled by the driver core, so
* nothing to do here.
*/
- if (par->num_genpds <= 1)
+ if (err <= 1)
return 0;
par->genpds = devm_kcalloc(dev, par->num_genpds, sizeof(*par->genpds),
@@ -485,6 +485,12 @@ static int simplefb_attach_genpds(struct simplefb_par *par,
if (!par->genpd_links)
return -ENOMEM;
+ /*
+ * Set num_genpds only after genpds and genpd_links are allocated to
+ * exit early from simplefb_detach_genpds() without full initialisation.
+ */
+ par->num_genpds = err;
+
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 +512,10 @@ 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,
--
Janne Grunau <j@...nau.net>
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