From: Helge Deller Date: Sat, 27 May 2023 06:41:09 +0000 (+0200) Subject: fbcon: Fix null-ptr-deref in soft_cursor X-Git-Tag: v6.1.37~531 X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=3270095f6eb52b50b8c6844594bdd650258aac2b;p=platform%2Fkernel%2Flinux-starfive.git fbcon: Fix null-ptr-deref in soft_cursor 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 Reported-by: syzbot+d910bd780e6efac35869@syzkaller.appspotmail.com Acked-by: Sam Ravnborg Cc: stable@kernel.org Signed-off-by: Greg Kroah-Hartman --- diff --git a/drivers/video/fbdev/core/bitblit.c b/drivers/video/fbdev/core/bitblit.c index f98e8f2..8587c9d 100644 --- 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 *vc, struct fb_info *info, int mode, 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));