From d78bd6cc68276bd57f766f7cb98bfe32c23ab327 Mon Sep 17 00:00:00 2001
From: Helge Deller <deller@gmx.de>
Date: Sat, 27 May 2023 08:41:09 +0200
Subject: fbcon: Fix null-ptr-deref in soft_cursor
Git-commit: d78bd6cc68276bd57f766f7cb98bfe32c23ab327
Patch-mainline: v6.4-rc5
References: bsc#1154048
syzbot repored this bug in the softcursor code:
BUG: KASAN: null-ptr-deref in soft_cursor+0x384/0x6b4 drivers/video/fbdev/core/softcursor.c:70
Read of size 16 at addr 0000000000000200 by task kworker/u4:1/12
CPU: 0 PID: 12 Comm: kworker/u4:1 Not tainted 6.4.0-rc3-syzkaller-geb0f1697d729 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/28/2023
Workqueue: events_power_efficient fb_flashcursor
Call trace:
dump_backtrace+0x1b8/0x1e4 arch/arm64/kernel/stacktrace.c:233
show_stack+0x2c/0x44 arch/arm64/kernel/stacktrace.c:240
__dump_stack lib/dump_stack.c:88 [inline]
dump_stack_lvl+0xd0/0x124 lib/dump_stack.c:106
print_report+0xe4/0x514 mm/kasan/report.c:465
kasan_report+0xd4/0x130 mm/kasan/report.c:572
kasan_check_range+0x264/0x2a4 mm/kasan/generic.c:187
__asan_memcpy+0x3c/0x84 mm/kasan/shadow.c:105
soft_cursor+0x384/0x6b4 drivers/video/fbdev/core/softcursor.c:70
bit_cursor+0x113c/0x1a64 drivers/video/fbdev/core/bitblit.c:377
fb_flashcursor+0x35c/0x54c drivers/video/fbdev/core/fbcon.c:380
process_one_work+0x788/0x12d4 kernel/workqueue.c:2405
worker_thread+0x8e0/0xfe8 kernel/workqueue.c:2552
kthread+0x288/0x310 kernel/kthread.c:379
ret_from_fork+0x10/0x20 arch/arm64/kernel/entry.S:853
This fix let bit_cursor() bail out early when a font bitmap
isn't available yet.
Signed-off-by: Helge Deller <deller@gmx.de>
Reported-by: syzbot+d910bd780e6efac35869@syzkaller.appspotmail.com
Acked-by: Sam Ravnborg <sam@ravnborg.org>
Cc: stable@kernel.org
Acked-by: Thomas Zimmermann <tzimmermann@suse.com>
---
drivers/video/console/bitblit.c | 3 +++
1 file changed, 3 insertions(+)
--- a/drivers/video/console/bitblit.c
+++ b/drivers/video/console/bitblit.c
@@ -256,6 +256,9 @@ static void bit_cursor(struct vc_data *v
y += softback_lines;
}
+ if (!vc->vc_font.data)
+ return;
+
c = scr_readw((u16 *) vc->vc_pos);
attribute = get_attribute(info, c);
src = vc->vc_font.data + ((c & charmask) * (w * vc->vc_font.height));