kernel/linux.git/drivers/video/fbdev/core/fbmem.c, branch v6.1.168

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

2025-12-06T21:12:10+00:00

commit a1f3058930745d2b938b6b4f5bd9630dc74b26b7 upstream. 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. Signed-off-by: Quanmin Yan Reviewed-by: Thomas Zimmermann Signed-off-by: Helge Deller Cc: stable@vger.kernel.org Signed-off-by: Greg Kroah-Hartman

fbdev: fix potential buffer overflow in do_register_framebuffer()

2025-08-28T14:25:59+00:00

[ Upstream commit 523b84dc7ccea9c4d79126d6ed1cf9033cf83b05 ] The current implementation may lead to buffer overflow when: 1. Unregistration creates NULL gaps in registered_fb[] 2. All array slots become occupied despite num_registered_fb < FB_MAX 3. The registration loop exceeds array bounds Add boundary check to prevent registered_fb[FB_MAX] access. Signed-off-by: Yongzhen Zhang Signed-off-by: Helge Deller Signed-off-by: Sasha Levin

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

2025-07-06T08:57:57+00:00

[ Upstream commit 17186f1f90d34fa701e4f14e6818305151637b9e ] If fb_add_videomode() in do_register_framebuffer() fails to allocate memory for fb_videomode, it will later 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 ================================================================ Even though fbcon_init() checks beforehand if fb_match_mode() in var_to_display() fails, it can not prevent the panic because fbcon_init() does not return error code. Considering this and the comment in the code about fb_match_mode() returning NULL - "This should not happen" - it is better to prevent registering the fb_info if its mode was not set successfully. Also move fb_add_videomode() closer to the beginning of do_register_framebuffer() to avoid having to do the cleanup on fail. 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: Sasha Levin

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

2025-06-27T10:07:29+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

fbmem: Reject FB_ACTIVATE_KD_TEXT from userspace

2023-04-20T10:35:06+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: Fix invalid page access after closing deferred I/O devices

2023-02-22T11:59:46+00:00

commit 3efc61d95259956db25347e2a9562c3e54546e20 upstream. 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 Signed-off-by: Greg Kroah-Hartman

fbdev: Make registered_fb[] private to fbmem.c

2022-07-27T07:40:18+00:00

No driver access this anymore, except for the olpc dcon fbdev driver but that has been marked as broken anyways by commit de0952f267ff ("staging: olpc_dcon: mark driver as broken"). Signed-off-by: Daniel Vetter Signed-off-by: Daniel Vetter Reviewed-by: Javier Martinez Canillas Signed-off-by: Javier Martinez Canillas Signed-off-by: Thomas Zimmermann Acked-by: Thomas Zimmermann Link: https://patchwork.freedesktop.org/patch/msgid/20220725075400.68478-1-javierm@redhat.com

fbdev: Remove conflict-handling code

2022-07-19T11:19:11+00:00

Remove the call to do_remove_conflicting_framebuffers() from the framebuffer registration. Aperture helpers take care of removing conflicting devices. With all ownership information stored in the aperture datastrcutures, remove remove_conflicting_framebuffers() entirely. This change also rectifies DRM generic-framebuffer registration, which tried to unregister conflicting framebuffers, even though it's entirely build on top of DRM. v2: * remove internal aperture-overlap helpers, which are now unused Signed-off-by: Thomas Zimmermann Reviewed-by: Javier Martinez Canillas Link: https://patchwork.freedesktop.org/patch/msgid/20220718072322.8927-12-tzimmermann@suse.de

fbdev: Acquire framebuffer apertures for firmware devices

2022-07-19T11:19:11+00:00

When registering a generic framebuffer, automatically acquire ownership of the framebuffer's I/O range. The device will now be handled by the aperture helpers. Fbdev-based conflict handling is no longer required. v2: * use fb_ prefix instead of fbm_ (Javier) Signed-off-by: Thomas Zimmermann Reviewed-by: Javier Martinez Canillas Link: https://patchwork.freedesktop.org/patch/msgid/20220718072322.8927-11-tzimmermann@suse.de

video: Provide constants for VGA I/O range

2022-07-19T11:19:11+00:00

Provide VGA_FB_ constants for the VGA framebuffer I/O range and convert fbdev code. In the case of vga16fb, this is a rename of the existing constants VGA_FB_PHYS and VGA_FB_PHYS_LEN. v2: * clarify relationship with old constants in vga16fb (Javier) Signed-off-by: Thomas Zimmermann Reviewed-by: Javier Martinez Canillas Link: https://patchwork.freedesktop.org/patch/msgid/20220718072322.8927-9-tzimmermann@suse.de