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SubjectKASAN: null-ptr-deref Read in do_con_trol
From
Hello,

syzbot found the following crash on:

HEAD commit: f2850dd5 Merge tag 'kbuild-fixes-v5.6' of git://git.kernel..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=16afe07ee00000
kernel config: https://syzkaller.appspot.com/x/.config?x=735296e4dd620b10
dashboard link: https://syzkaller.appspot.com/bug?extid=70b2d05eec48639a904e
compiler: gcc (GCC) 9.0.0 20181231 (experimental)
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=154ac65ee00000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=15d296b5e00000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+70b2d05eec48639a904e@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: null-ptr-deref in memcpy include/linux/string.h:381 [inline]
BUG: KASAN: null-ptr-deref in scr_memcpyw include/linux/vt_buffer.h:49 [inline]
BUG: KASAN: null-ptr-deref in delete_char drivers/tty/vt/vt.c:852 [inline]
BUG: KASAN: null-ptr-deref in csi_P drivers/tty/vt/vt.c:1985 [inline]
BUG: KASAN: null-ptr-deref in do_con_trol+0x3b9/0x61b0 drivers/tty/vt/vt.c:2379
Read of size 4294967294 at addr 0000000000000012 by task syz-executor841/9673

CPU: 0 PID: 9673 Comm: syz-executor841 Not tainted 5.6.0-rc1-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
__kasan_report.cold+0x5/0x32 mm/kasan/report.c:510
kasan_report+0x12/0x20 mm/kasan/common.c:641
check_memory_region_inline mm/kasan/generic.c:185 [inline]
check_memory_region+0x134/0x1a0 mm/kasan/generic.c:192
memcpy+0x24/0x50 mm/kasan/common.c:127
memcpy include/linux/string.h:381 [inline]
scr_memcpyw include/linux/vt_buffer.h:49 [inline]
delete_char drivers/tty/vt/vt.c:852 [inline]
csi_P drivers/tty/vt/vt.c:1985 [inline]
do_con_trol+0x3b9/0x61b0 drivers/tty/vt/vt.c:2379
do_con_write.part.0+0xfd9/0x1ef0 drivers/tty/vt/vt.c:2797
do_con_write drivers/tty/vt/vt.c:2565 [inline]
con_write+0x46/0xd0 drivers/tty/vt/vt.c:3135
process_output_block drivers/tty/n_tty.c:595 [inline]
n_tty_write+0x40e/0x1080 drivers/tty/n_tty.c:2333
do_tty_write drivers/tty/tty_io.c:962 [inline]
tty_write+0x496/0x7f0 drivers/tty/tty_io.c:1046
__vfs_write+0x8a/0x110 fs/read_write.c:494
vfs_write+0x268/0x5d0 fs/read_write.c:558
ksys_write+0x14f/0x290 fs/read_write.c:611
__do_sys_write fs/read_write.c:623 [inline]
__se_sys_write fs/read_write.c:620 [inline]
__x64_sys_write+0x73/0xb0 fs/read_write.c:620
do_syscall_64+0xfa/0x790 arch/x86/entry/common.c:294
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x4404f9
Code: 18 89 d0 c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 0f 83 5b 14 fc ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007ffefa71b898 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00000000004002c8 RCX: 00000000004404f9
RDX: 0000000000000078 RSI: 0000000020000140 RDI: 0000000000000004
RBP: 00000000006ca018 R08: 0000000000000000 R09: 00000000004002c8
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000401de0
R13: 0000000000401e70 R14: 0000000000000000 R15: 0000000000000000
==================================================================


---
This bug is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
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syzbot will keep track of this bug report. See:
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syzbot can test patches for this bug, for details see:
https://goo.gl/tpsmEJ#testing-patches

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