Re: KASAN: global-out-of-bounds Read in precalculate_color

[syzbot]

syzbot has found a reproducer for the following crash on:

HEAD commit:    46cf053e Linux 5.5-rc3
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=11932ce1e00000
kernel config:  https://syzkaller.appspot.com/x/.config?x=ed9d672709340e35
dashboard link: https://syzkaller.appspot.com/bug?extid=02d9172bf4c43104cd70
compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=14861a49e00000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1794423ee00000

The bug was bisected to:

commit 7594bf37ae9ffc434da425120c576909eb33b0bc
Author: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Date:   Mon Jul 17 02:53:08 2017 +0000

    9p: untangle ->poll() mess

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=15e323a6e00000
console output: https://syzkaller.appspot.com/x/log.txt?x=13e323a6e00000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+02d9172bf4c43104cd70@xxxxxxxxxxxxxxxxxxxxxxxxx
Fixes: 7594bf37ae9f ("9p: untangle ->poll() mess")

==================================================================
BUG: KASAN: global-out-of-bounds in precalculate_color+0x2154/0x2480  
drivers/media/common/v4l2-tpg/v4l2-tpg-core.c:942
Read of size 1 at addr ffffffff88b3d3f9 by task vivid-000-vid-c/9278

CPU: 0 PID: 9278 Comm: vivid-000-vid-c Not tainted 5.5.0-rc3-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x197/0x210 lib/dump_stack.c:118
 print_address_description.constprop.0.cold+0x5/0x30b mm/kasan/report.c:374
 __kasan_report.cold+0x1b/0x41 mm/kasan/report.c:506
 kasan_report+0x12/0x20 mm/kasan/common.c:639
 __asan_report_load1_noabort+0x14/0x20 mm/kasan/generic_report.c:132
 precalculate_color+0x2154/0x2480  
drivers/media/common/v4l2-tpg/v4l2-tpg-core.c:942
 tpg_precalculate_colors drivers/media/common/v4l2-tpg/v4l2-tpg-core.c:1093  
[inline]
 tpg_recalc+0x561/0x2850 drivers/media/common/v4l2-tpg/v4l2-tpg-core.c:2118
 tpg_calc_text_basep+0xa1/0x290  
drivers/media/common/v4l2-tpg/v4l2-tpg-core.c:2136
 vivid_fillbuff+0x1a5f/0x3af0  
drivers/media/platform/vivid/vivid-kthread-cap.c:466
 vivid_thread_vid_cap_tick+0x8cf/0x2210  
drivers/media/platform/vivid/vivid-kthread-cap.c:727
 vivid_thread_vid_cap+0x5d8/0xa60  
drivers/media/platform/vivid/vivid-kthread-cap.c:866
 kthread+0x361/0x430 kernel/kthread.c:255
 ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:352

The buggy address belongs to the variable:
 kbd_keycodes+0x119/0x760

Memory state around the buggy address:
 ffffffff88b3d280: fa fa fa fa 00 00 04 fa fa fa fa fa 00 00 00 00
 ffffffff88b3d300: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> ffffffff88b3d380: 00 00 00 00 00 00 00 00 00 00 00 00 fa fa fa fa
                                                                ^
 ffffffff88b3d400: 00 00 00 00 07 fa fa fa fa fa fa fa 00 00 00 00
 ffffffff88b3d480: 00 fa fa fa fa fa fa fa 02 fa fa fa fa fa fa fa
==================================================================