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Jiri Slaby (SUSE)gregkh
Jiri Slaby (SUSE)
authored and
gregkh
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fbcon: always restore the old font data in fbcon_do_set_font()
[ Upstream commit 00d6a28 ] Commit a5a9230 (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: a5a9230 ("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: Sasha Levin <[email protected]>
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1 file changed

Lines changed: 3 additions & 5 deletions

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‎drivers/video/fbdev/core/fbcon.c‎

Lines changed: 3 additions & 5 deletions
Original file line numberDiff line numberDiff line change
@@ -2400,11 +2400,9 @@ static int fbcon_do_set_font(struct vc_data *vc, int w, int h, int charcount,
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struct fbcon_ops *ops = info->fbcon_par;
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struct fbcon_display *p = &fb_display[vc->vc_num];
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int resize, ret, old_userfont, old_width, old_height, old_charcount;
2403-
char *old_data = NULL;
2403+
u8 *old_data = vc->vc_font.data;
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resize = (w != vc->vc_font.width) || (h != vc->vc_font.height);
2406-
if (p->userfont)
2407-
old_data = vc->vc_font.data;
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vc->vc_font.data = (void *)(p->fontdata = data);
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old_userfont = p->userfont;
24102408
if ((p->userfont = userfont))
@@ -2438,13 +2436,13 @@ static int fbcon_do_set_font(struct vc_data *vc, int w, int h, int charcount,
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update_screen(vc);
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}
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2441-
if (old_data && (--REFCOUNT(old_data) == 0))
2439+
if (old_userfont && (--REFCOUNT(old_data) == 0))
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kfree(old_data - FONT_EXTRA_WORDS * sizeof(int));
24432441
return 0;
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err_out:
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p->fontdata = old_data;
2447-
vc->vc_font.data = (void *)old_data;
2445+
vc->vc_font.data = old_data;
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if (userfont) {
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p->userfont = old_userfont;

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