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 <[e-mail]>
Cc: [e-mail]
Fixes: 92a511a568e44 ("fbdev/simplefb: Add support for generic power-domains")
Signed-off-by: Janne Grunau <[e-mail]>
Reviewed-by: Hans de Goede <[e-mail]>
Signed-off-by: Helge Deller <[e-mail]>

drivers/video/fbdev/simplefb.c

···
 
 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
···
 
 	simplefb_regulators_destroy(info->par);
 	simplefb_clocks_destroy(info->par);
+	simplefb_detach_genpds(info->par);
 	if (info->screen_base)
 		iounmap(info->screen_base);
 
···
 		if (!IS_ERR_OR_NULL(par->genpds[i]))
 			dev_pm_domain_detach(par->genpds[i], true);
 	}
+	par->num_genpds = 0;
 }
 
 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",
···
 		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) {
+		par->num_genpds = num_genpds;
 		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);
···
 			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)
 {
···
 	ret = devm_aperture_acquire_for_platform_device(pdev, par->base, par->size);
 	if (ret) {
 		dev_err(&pdev->dev, "Unable to acquire aperture: %d\n", ret);
-		goto error_regulators;
+		goto error_genpds;
 	}
 	ret = register_framebuffer(info);
 	if (ret < 0) {
 		dev_err(&pdev->dev, "Unable to register simplefb: %d\n", ret);
-		goto error_regulators;
+		goto error_genpds;
 	}
 
 	dev_info(&pdev->dev, "fb%d: simplefb registered!\n", info->node);
 
 	return 0;
 
+error_genpds:
+	simplefb_detach_genpds(par);
 error_regulators:
 	simplefb_regulators_destroy(par);
 error_clocks: