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linux/drivers/video
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Jiri Slaby (SUSE) 2f91a96b89 fbcon: always restore the old font data in fbcon_do_set_font() 
[ Upstream commit 00d6a284fc ]

Commit a5a923038d (fbdev: fbcon: Properly revert changes when
vc_resize() failed) started restoring old font data upon failure (of
vc_resize()). But it performs so only for user fonts. It means that the
"system"/internal fonts are not restored at all. So in result, the very
first call to fbcon_do_set_font() performs no restore at all upon
failing vc_resize().

This can be reproduced by Syzkaller to crash the system on the next
invocation of font_get(). It's rather hard to hit the allocation failure
in vc_resize() on the first font_set(), but not impossible. Esp. if
fault injection is used to aid the execution/failure. It was
demonstrated by Sirius:
  BUG: unable to handle page fault for address: fffffffffffffff8
  #PF: supervisor read access in kernel mode
  #PF: error_code(0x0000) - not-present page
  PGD cb7b067 P4D cb7b067 PUD cb7d067 PMD 0
  Oops: 0000 [#1] PREEMPT SMP KASAN
  CPU: 1 PID: 8007 Comm: poc Not tainted 6.7.0-g9d1694dc91ce #20
  Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1 04/01/2014
  RIP: 0010:fbcon_get_font+0x229/0x800 drivers/video/fbdev/core/fbcon.c:2286
  Call Trace:
   <TASK>
   con_font_get drivers/tty/vt/vt.c:4558 [inline]
   con_font_op+0x1fc/0xf20 drivers/tty/vt/vt.c:4673
   vt_k_ioctl drivers/tty/vt/vt_ioctl.c:474 [inline]
   vt_ioctl+0x632/0x2ec0 drivers/tty/vt/vt_ioctl.c:752
   tty_ioctl+0x6f8/0x1570 drivers/tty/tty_io.c:2803
   vfs_ioctl fs/ioctl.c:51 [inline]
  ...

So restore the font data in any case, not only for user fonts. Note the
later 'if' is now protected by 'old_userfont' and not 'old_data' as the
latter is always set now. (And it is supposed to be non-NULL. Otherwise
we would see the bug above again.)

Signed-off-by: Jiri Slaby (SUSE) <jirislaby@kernel.org>
Fixes: a5a923038d ("fbdev: fbcon: Properly revert changes when vc_resize() failed")
Reported-and-tested-by: Ubisectech Sirius <bugreport@ubisectech.com>
Cc: Ubisectech Sirius <bugreport@ubisectech.com>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: Helge Deller <deller@gmx.de>
Cc: linux-fbdev@vger.kernel.org
Cc: dri-devel@lists.freedesktop.org
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20240208114411.14604-1-jirislaby@kernel.org
Signed-off-by: Sasha Levin <sashal@kernel.org>
History 2024-03-06 14:45:09 +00:00
..
backlight backlight: gpio_backlight: Drop output GPIO direction check for initial power state 2023-09-19 12:27:59 +02:00
console fbdev: Move fbdev drivers from strlcpy to strscpy 2022-08-24 22:06:15 +02:00
fbdev fbcon: always restore the old font data in fbcon_do_set_font() 2024-03-06 14:45:09 +00:00
logo .gitignore: add SPDX License Identifier 2020-03-25 11:50:48 +01:00
aperture.c video/aperture: Move vga handling to pci function 2023-08-30 16:10:58 +02:00
display_timing.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 428 2019-06-05 17:37:16 +02:00
hdmi.c video/hdmi: Add audio_infoframe packing for DP 2022-09-04 15:31:59 +03:00
Kconfig drm: Implement DRM aperture helpers under video/ 2022-06-27 11:07:55 +02:00
Makefile drm: Implement DRM aperture helpers under video/ 2022-06-27 11:07:55 +02:00
of_display_timing.c video: fbdev: of: display_timing: Remove a redundant zeroing of memory 2022-04-04 08:55:23 +02:00
of_videomode.c video: Fix kernel-doc warnings in of_display_timing + of_videomode 2020-11-29 22:42:17 +01:00
vgastate.c Video: vgastate: fixed a spacing coding style 2018-10-08 12:57:35 +02:00
videomode.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 428 2019-06-05 17:37:16 +02:00