kernel/linux.git/drivers/video/fbdev/core/fbmem.c, branch v5.15.210

fbcon: Set fb_display[i]->mode to NULL when the mode is released

2026-04-18T08:33:35+00:00

[ Upstream commit a1f3058930745d2b938b6b4f5bd9630dc74b26b7 ] Recently, we discovered the following issue through syzkaller: BUG: KASAN: slab-use-after-free in fb_mode_is_equal+0x285/0x2f0 Read of size 4 at addr ff11000001b3c69c by task syz.xxx ... Call Trace: dump_stack_lvl+0xab/0xe0 print_address_description.constprop.0+0x2c/0x390 print_report+0xb9/0x280 kasan_report+0xb8/0xf0 fb_mode_is_equal+0x285/0x2f0 fbcon_mode_deleted+0x129/0x180 fb_set_var+0xe7f/0x11d0 do_fb_ioctl+0x6a0/0x750 fb_ioctl+0xe0/0x140 __x64_sys_ioctl+0x193/0x210 do_syscall_64+0x5f/0x9c0 entry_SYSCALL_64_after_hwframe+0x76/0x7e Based on experimentation and analysis, during framebuffer unregistration, only the memory of fb_info->modelist is freed, without setting the corresponding fb_display[i]->mode to NULL for the freed modes. This leads to UAF issues during subsequent accesses. Here's an example of reproduction steps: 1. With /dev/fb0 already registered in the system, load a kernel module to register a new device /dev/fb1; 2. Set fb1's mode to the global fb_display[] array (via FBIOPUT_CON2FBMAP); 3. Switch console from fb to VGA (to allow normal rmmod of the ko); 4. Unload the kernel module, at this point fb1's modelist is freed, leaving a wild pointer in fb_display[]; 5. Trigger the bug via system calls through fb0 attempting to delete a mode from fb0. Add a check in do_unregister_framebuffer(): if the mode to be freed exists in fb_display[], set the corresponding mode pointer to NULL. [ The context change is due to the commit 2c0c19b681d5 ("fbdev: fbmem: Fix double free of 'fb_info->pixmap.addr'") in v5.16 which is irrelevant to the logic of this patch. ] Signed-off-by: Quanmin Yan Reviewed-by: Thomas Zimmermann Signed-off-by: Helge Deller Cc: stable@vger.kernel.org Signed-off-by: Johnny Hao Signed-off-by: Sasha Levin

Revert "fbdev: Disable sysfb device registration when removing conflicting FBs"

2025-10-02T11:38:58+00:00

This reverts commit 13d28e0c79cbf69fc6f145767af66905586c1249. Commit ee7a69aa38d8 ("fbdev: Disable sysfb device registration when removing conflicting FBs") was backported to 5.15.y LTS. This causes a regression where all virtual consoles stop responding during boot at: "Populating /dev with existing devices through uevents ..." Reverting the commit fixes the regression. Signed-off-by: Brett A C Sheffield Signed-off-by: Sasha Levin

fbdev: Fix fb_set_var to prevent null-ptr-deref in fb_videomode_to_var

2025-06-27T10:05:26+00:00

commit 05f6e183879d9785a3cdf2f08a498bc31b7a20aa upstream. If fb_add_videomode() in fb_set_var() fails to allocate memory for fb_videomode, later it may lead to a null-ptr dereference in fb_videomode_to_var(), as the fb_info is registered while not having the mode in modelist that is expected to be there, i.e. the one that is described in fb_info->var. ================================================================ general protection fault, probably for non-canonical address 0xdffffc0000000001: 0000 [#1] PREEMPT SMP KASAN NOPTI KASAN: null-ptr-deref in range [0x0000000000000008-0x000000000000000f] CPU: 1 PID: 30371 Comm: syz-executor.1 Not tainted 5.10.226-syzkaller #0 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.12.0-1 04/01/2014 RIP: 0010:fb_videomode_to_var+0x24/0x610 drivers/video/fbdev/core/modedb.c:901 Call Trace: display_to_var+0x3a/0x7c0 drivers/video/fbdev/core/fbcon.c:929 fbcon_resize+0x3e2/0x8f0 drivers/video/fbdev/core/fbcon.c:2071 resize_screen drivers/tty/vt/vt.c:1176 [inline] vc_do_resize+0x53a/0x1170 drivers/tty/vt/vt.c:1263 fbcon_modechanged+0x3ac/0x6e0 drivers/video/fbdev/core/fbcon.c:2720 fbcon_update_vcs+0x43/0x60 drivers/video/fbdev/core/fbcon.c:2776 do_fb_ioctl+0x6d2/0x740 drivers/video/fbdev/core/fbmem.c:1128 fb_ioctl+0xe7/0x150 drivers/video/fbdev/core/fbmem.c:1203 vfs_ioctl fs/ioctl.c:48 [inline] __do_sys_ioctl fs/ioctl.c:753 [inline] __se_sys_ioctl fs/ioctl.c:739 [inline] __x64_sys_ioctl+0x19a/0x210 fs/ioctl.c:739 do_syscall_64+0x33/0x40 arch/x86/entry/common.c:46 entry_SYSCALL_64_after_hwframe+0x67/0xd1 ================================================================ The reason is that fb_info->var is being modified in fb_set_var(), and then fb_videomode_to_var() is called. If it fails to add the mode to fb_info->modelist, fb_set_var() returns error, but does not restore the old value of fb_info->var. Restore fb_info->var on failure the same way it is done earlier in the function. Found by Linux Verification Center (linuxtesting.org) with Syzkaller. Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") Cc: stable@vger.kernel.org Signed-off-by: Murad Masimov Signed-off-by: Helge Deller Signed-off-by: Greg Kroah-Hartman

fbdev: Fix invalid page access after closing deferred I/O devices

2024-02-23T07:55:13+00:00

[ Upstream commit 3efc61d95259956db25347e2a9562c3e54546e20 ] When a fbdev with deferred I/O is once opened and closed, the dirty pages still remain queued in the pageref list, and eventually later those may be processed in the delayed work. This may lead to a corruption of pages, hitting an Oops. This patch makes sure to cancel the delayed work and clean up the pageref list at closing the device for addressing the bug. A part of the cleanup code is factored out as a new helper function that is called from the common fb_release(). Reviewed-by: Patrik Jakobsson Cc: Signed-off-by: Takashi Iwai Tested-by: Miko Larsson Fixes: 56c134f7f1b5 ("fbdev: Track deferred-I/O pages in pageref struct") Reviewed-by: Thomas Zimmermann Signed-off-by: Thomas Zimmermann Link: https://patchwork.freedesktop.org/patch/msgid/20230129082856.22113-1-tiwai@suse.de Stable-dep-of: 33cd6ea9c067 ("fbdev: flush deferred IO before closing") Signed-off-by: Sasha Levin

fbmem: Reject FB_ACTIVATE_KD_TEXT from userspace

2023-04-20T10:13:52+00:00

commit 6fd33a3333c7916689b8f051a185defe4dd515b0 upstream. This is an oversight from dc5bdb68b5b3 ("drm/fb-helper: Fix vt restore") - I failed to realize that nasty userspace could set this. It's not pretty to mix up kernel-internal and userspace uapi flags like this, but since the entire fb_var_screeninfo structure is uapi we'd need to either add a new parameter to the ->fb_set_par callback and fb_set_par() function, which has a _lot_ of users. Or some other fairly ugly side-channel int fb_info. Neither is a pretty prospect. Instead just correct the issue at hand by filtering out this kernel-internal flag in the ioctl handling code. Reviewed-by: Javier Martinez Canillas Acked-by: Maarten Lankhorst Signed-off-by: Daniel Vetter Fixes: dc5bdb68b5b3 ("drm/fb-helper: Fix vt restore") Cc: Alex Deucher Cc: shlomo@fastmail.com Cc: Michel Dänzer Cc: Noralf Trønnes Cc: Thomas Zimmermann Cc: Daniel Vetter Cc: Maarten Lankhorst Cc: Maxime Ripard Cc: David Airlie Cc: Daniel Vetter Cc: dri-devel@lists.freedesktop.org Cc: # v5.7+ Cc: Bartlomiej Zolnierkiewicz Cc: Geert Uytterhoeven Cc: Nathan Chancellor Cc: Qiujun Huang Cc: Peter Rosin Cc: linux-fbdev@vger.kernel.org Cc: Helge Deller Cc: Sam Ravnborg Cc: Geert Uytterhoeven Cc: Samuel Thibault Cc: Tetsuo Handa Cc: Shigeru Yoshida Link: https://patchwork.freedesktop.org/patch/msgid/20230404193934.472457-1-daniel.vetter@ffwll.ch Signed-off-by: Greg Kroah-Hartman

fbdev: Disable sysfb device registration when removing conflicting FBs

2022-07-21T19:24:35+00:00

[ Upstream commit ee7a69aa38d87a3bbced7b8245c732c05ed0c6ec ] The platform devices registered by sysfb match with firmware-based DRM or fbdev drivers, that are used to have early graphics using a framebuffer provided by the system firmware. DRM or fbdev drivers later are probed and remove conflicting framebuffers, leading to these platform devices for generic drivers to be unregistered. But the current solution has a race, since the sysfb_init() function could be called after a DRM or fbdev driver is probed and request to unregister the devices for drivers with conflicting framebuffes. To prevent this, disable any future sysfb platform device registration by calling sysfb_disable(), if a driver requests to remove the conflicting framebuffers. Suggested-by: Daniel Vetter Signed-off-by: Javier Martinez Canillas Reviewed-by: Daniel Vetter Link: https://patchwork.freedesktop.org/patch/msgid/20220607182338.344270-4-javierm@redhat.com Signed-off-by: Sasha Levin

fbcon: Prevent that screen size is smaller than font size

2022-07-12T14:35:09+00:00

commit e64242caef18b4a5840b0e7a9bff37abd4f4f933 upstream. We need to prevent that users configure a screen size which is smaller than the currently selected font size. Otherwise rendering chars on the screen will access memory outside the graphics memory region. This patch adds a new function fbcon_modechange_possible() which implements this check and which later may be extended with other checks if necessary. The new function is called from the FBIOPUT_VSCREENINFO ioctl handler in fbmem.c, which will return -EINVAL if userspace asked for a too small screen size. Signed-off-by: Helge Deller Reviewed-by: Geert Uytterhoeven Cc: stable@vger.kernel.org # v5.4+ Signed-off-by: Greg Kroah-Hartman

fbmem: Check virtual screen sizes in fb_set_var()

2022-07-12T14:35:09+00:00

commit 6c11df58fd1ac0aefcb3b227f72769272b939e56 upstream. Verify that the fbdev or drm driver correctly adjusted the virtual screen sizes. On failure report the failing driver and reject the screen size change. Signed-off-by: Helge Deller Reviewed-by: Geert Uytterhoeven Cc: stable@vger.kernel.org # v5.4+ Signed-off-by: Greg Kroah-Hartman

fbdev: fbmem: Fix logo center image dx issue

2022-07-12T14:35:09+00:00

commit 955f04766d4e6eb94bf3baa539e096808c74ebfb upstream. Image.dx gets wrong value because of missing '()'. If xres == logo->width and n == 1, image.dx = -16. Signed-off-by: Guiling Deng Fixes: 3d8b1933eb1c ("fbdev: fbmem: add config option to center the bootup logo") Cc: stable@vger.kernel.org # v5.0+ Signed-off-by: Helge Deller Signed-off-by: Greg Kroah-Hartman

Revert "fbdev: Make fb_release() return -ENODEV if fbdev was unregistered"

2022-05-25T07:57:35+00:00

[ Upstream commit 135332f34ba2662bc1e32b5c612e06a8cc41a053 ] This reverts commit aafa025c76dcc7d1a8c8f0bdefcbe4eb480b2f6a. That commit attempted to fix a NULL pointer dereference, caused by the struct fb_info associated with a framebuffer device to not longer be valid when the file descriptor was closed. The issue was exposed by commit 27599aacbaef ("fbdev: Hot-unplug firmware fb devices on forced removal"), which added a new path that goes through the struct device removal instead of directly unregistering the fb. Most fbdev drivers have issues with the fb_info lifetime, because call to framebuffer_release() from their driver's .remove callback, rather than doing from fbops.fb_destroy callback. This meant that due to this switch, the fb_info was now destroyed too early, while references still existed, while before it was simply leaked. The patch we're reverting here reinstated that leak, hence "fixed" the regression. But the proper solution is to fix the drivers to not release the fb_info too soon. Suggested-by: Daniel Vetter Signed-off-by: Javier Martinez Canillas Reviewed-by: Daniel Vetter Link: https://patchwork.freedesktop.org/patch/msgid/20220504115917.758787-1-javierm@redhat.com Signed-off-by: Sasha Levin