From: Helge Deller <deller@xxxxxx> commit d78bd6cc68276bd57f766f7cb98bfe32c23ab327 upstream. 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@xxxxxx> Reported-by: syzbot+d910bd780e6efac35869@xxxxxxxxxxxxxxxxxxxxxxxxx Acked-by: Sam Ravnborg <sam@xxxxxxxxxxxx> Cc: stable@xxxxxxxxxx Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- drivers/video/fbdev/core/bitblit.c | 3 +++ 1 file changed, 3 insertions(+) --- a/drivers/video/fbdev/core/bitblit.c +++ b/drivers/video/fbdev/core/bitblit.c @@ -247,6 +247,9 @@ static void bit_cursor(struct vc_data *v cursor.set = 0; + 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));
