bisecting fixing commit since 3d40d7117e353b84627c1e8c5ed9ae0b1237ef5c
building syzkaller on ddc3e85997efdad885e208db6a98bca86e5dd52f
testing commit 3d40d7117e353b84627c1e8c5ed9ae0b1237ef5c with gcc (GCC) 8.1.0
kernel signature: c94c537e23da32c5a54b2ef7bcc1b68380694f05763f2aaacd6c3c9fa60d6064
all runs: crashed: KASAN: null-ptr-deref Read in insert_char
testing current HEAD 6dd0e32665e591e9debe3edaf73c2f8135bf047e
testing commit 6dd0e32665e591e9debe3edaf73c2f8135bf047e with gcc (GCC) 8.1.0
kernel signature: 2ed5338476041136fea468a5401d309a2fd3176399a91f751f09c2e44ffec40c
all runs: crashed: KASAN: null-ptr-deref Read in insert_char
revisions tested: 2, total time: 24m51.777589599s (build: 18m0.375057962s, test: 6m1.307202367s)
the crash still happens on HEAD
commit msg: Linux 4.19.115
crash: KASAN: null-ptr-deref Read in insert_char
IPv6: ADDRCONF(NETDEV_UP): macvlan1: link is not ready
IPv6: ADDRCONF(NETDEV_CHANGE): macvlan0: link becomes ready
IPv6: ADDRCONF(NETDEV_CHANGE): macvlan1: link becomes ready
==================================================================
BUG: KASAN: null-ptr-deref in memmove include/linux/string.h:363 [inline]
BUG: KASAN: null-ptr-deref in scr_memmovew include/linux/vt_buffer.h:68 [inline]
BUG: KASAN: null-ptr-deref in insert_char+0x1e2/0x440 drivers/tty/vt/vt.c:839
Read of size 4294967294 at addr 0000000000000010 by task syz-executor.4/7772

CPU: 0 PID: 7772 Comm: syz-executor.4 Not tainted 4.19.115-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+0x123/0x177 lib/dump_stack.c:118
 kasan_report_error mm/kasan/report.c:352 [inline]
 kasan_report.cold.9+0x6d/0x309 mm/kasan/report.c:412
 check_memory_region_inline mm/kasan/kasan.c:260 [inline]
 check_memory_region+0x13e/0x1b0 mm/kasan/kasan.c:267
 memmove+0x23/0x50 mm/kasan/kasan.c:293
 memmove include/linux/string.h:363 [inline]
 scr_memmovew include/linux/vt_buffer.h:68 [inline]
 insert_char+0x1e2/0x440 drivers/tty/vt/vt.c:839
 csi_at drivers/tty/vt/vt.c:1989 [inline]
 do_con_trol+0x33e0/0x6370 drivers/tty/vt/vt.c:2436
 do_con_write.part.26+0xad0/0x1aa0 drivers/tty/vt/vt.c:2797
 do_con_write drivers/tty/vt/vt.c:2565 [inline]
 con_write+0x1f/0x80 drivers/tty/vt/vt.c:3132
 process_output_block drivers/tty/n_tty.c:593 [inline]
 n_tty_write+0x4a4/0x1060 drivers/tty/n_tty.c:2331
 do_tty_write drivers/tty/tty_io.c:960 [inline]
 tty_write+0x346/0x770 drivers/tty/tty_io.c:1044
 __vfs_write+0xe3/0x890 fs/read_write.c:485
 vfs_write+0x150/0x4d0 fs/read_write.c:549
 ksys_write+0x103/0x260 fs/read_write.c:599
 __do_sys_write fs/read_write.c:611 [inline]
 __se_sys_write fs/read_write.c:608 [inline]
 __x64_sys_write+0x6e/0xb0 fs/read_write.c:608
 do_syscall_64+0xd0/0x4e0 arch/x86/entry/common.c:293
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x45af49
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:00007f7260869c78 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 000000000045af49
RDX: 0000000000000078 RSI: 0000000020000000 RDI: 0000000000000004
RBP: 000000000075bf20 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007f726086a6d4
R13: 00000000004cce19 R14: 00000000004e81c0 R15: 00000000ffffffff
==================================================================