bisecting fixing commit since 829e6944699530c47739b5ef091f8137526c1494
building syzkaller on 5d7b90f1af2e3bf33992b75e7fcf0bab6bf49bd6
testing commit 829e6944699530c47739b5ef091f8137526c1494 with gcc (GCC) 8.1.0
kernel signature: ca8fc2670f11c0597860d5018325202af584037aa297883818decfc158b7698a
all runs: crashed: KASAN: null-ptr-deref Read in do_con_trol
testing current HEAD fb33c6510d5595144d585aa194d377cf74d31911
testing commit fb33c6510d5595144d585aa194d377cf74d31911 with gcc (GCC) 8.1.0
kernel signature: 40a290b07e276c92cc0f17c99479145ddffdbe709ba6bd099a65007939e34636
all runs: crashed: KASAN: null-ptr-deref Read in do_con_trol
revisions tested: 2, total time: 22m6.792381717s (build: 12m59.491943184s, test: 8m42.538743765s)
the crash still happens on HEAD
commit msg: Linux 5.6-rc6
crash: KASAN: null-ptr-deref Read in do_con_trol
==================================================================
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:1996 [inline]
BUG: KASAN: null-ptr-deref in do_con_trol+0x3c8b/0x63d0 drivers/tty/vt/vt.c:2390
Read of size 4294967294 at addr 0000000000000012 by task syz-executor.4/8871

CPU: 0 PID: 8871 Comm: syz-executor.4 Not tainted 5.6.0-rc6-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+0x12d/0x187 lib/dump_stack.c:118
 __kasan_report.cold.11+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+0x153/0x1d0 mm/kasan/generic.c:192
 memcpy+0x23/0x50 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:1996 [inline]
 do_con_trol+0x3c8b/0x63d0 drivers/tty/vt/vt.c:2390
 do_con_write.part.25+0xab6/0x1ad0 drivers/tty/vt/vt.c:2808
 do_con_write drivers/tty/vt/vt.c:2576 [inline]
 con_write+0x1f/0x80 drivers/tty/vt/vt.c:3144
 process_output_block drivers/tty/n_tty.c:595 [inline]
 n_tty_write+0x494/0xfa0 drivers/tty/n_tty.c:2333
 do_tty_write drivers/tty/tty_io.c:962 [inline]
 tty_write+0x371/0x7d0 drivers/tty/tty_io.c:1046
 __vfs_write+0x5e/0x110 fs/read_write.c:494
 vfs_write+0x18a/0x520 fs/read_write.c:558
 ksys_write+0x105/0x220 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+0x6e/0xb0 fs/read_write.c:620
 do_syscall_64+0xca/0x630 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x45c6c9
Code: ad b6 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 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 7b b6 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007f17349bfc78 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007f17349c06d4 RCX: 000000000045c6c9
RDX: 0000000000000078 RSI: 0000000020000140 RDI: 0000000000000004
RBP: 000000000076bf20 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000ffffffff
R13: 0000000000000ca8 R14: 00000000004ceba3 R15: 000000000076bf2c
==================================================================