This is a note to let you know that I've just added the patch titled
fbcon: always restore the old font data in fbcon_do_set_font()
to the 5.10-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
fbcon-always-restore-the-old-font-data-in-fbcon_do_set_font.patch
and it can be found in the queue-5.10 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <[email protected]> know about it.
>From 00d6a284fcf3fad1b7e1b5bc3cd87cbfb60ce03f Mon Sep 17 00:00:00 2001
From: "Jiri Slaby (SUSE)" <[email protected]>
Date: Thu, 8 Feb 2024 12:44:11 +0100
Subject: fbcon: always restore the old font data in fbcon_do_set_font()
From: Jiri Slaby (SUSE) <[email protected]>
commit 00d6a284fcf3fad1b7e1b5bc3cd87cbfb60ce03f upstream.
Commit a5a923038d70 (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) <[email protected]>
Fixes: a5a923038d70 ("fbdev: fbcon: Properly revert changes when vc_resize()
failed")
Reported-and-tested-by: Ubisectech Sirius <[email protected]>
Cc: Ubisectech Sirius <[email protected]>
Cc: Daniel Vetter <[email protected]>
Cc: Helge Deller <[email protected]>
Cc: [email protected]
Cc: [email protected]
Signed-off-by: Daniel Vetter <[email protected]>
Link:
https://patchwork.freedesktop.org/patch/msgid/[email protected]
Signed-off-by: Greg Kroah-Hartman <[email protected]>
---
drivers/video/fbdev/core/fbcon.c | 8 +++-----
1 file changed, 3 insertions(+), 5 deletions(-)
--- a/drivers/video/fbdev/core/fbcon.c
+++ b/drivers/video/fbdev/core/fbcon.c
@@ -2425,11 +2425,9 @@ static int fbcon_do_set_font(struct vc_d
struct fbcon_ops *ops = info->fbcon_par;
struct fbcon_display *p = &fb_display[vc->vc_num];
int resize, ret, old_userfont, old_width, old_height, old_charcount;
- char *old_data = NULL;
+ u8 *old_data = vc->vc_font.data;
resize = (w != vc->vc_font.width) || (h != vc->vc_font.height);
- if (p->userfont)
- old_data = vc->vc_font.data;
vc->vc_font.data = (void *)(p->fontdata = data);
old_userfont = p->userfont;
if ((p->userfont = userfont))
@@ -2463,13 +2461,13 @@ static int fbcon_do_set_font(struct vc_d
update_screen(vc);
}
- if (old_data && (--REFCOUNT(old_data) == 0))
+ if (old_userfont && (--REFCOUNT(old_data) == 0))
kfree(old_data - FONT_EXTRA_WORDS * sizeof(int));
return 0;
err_out:
p->fontdata = old_data;
- vc->vc_font.data = (void *)old_data;
+ vc->vc_font.data = old_data;
if (userfont) {
p->userfont = old_userfont;
Patches currently in stable-queue which might be from [email protected] are
queue-5.10/fbcon-always-restore-the-old-font-data-in-fbcon_do_set_font.patch
