bisecting fixing commit since a844dc4c544291470aa69edbe2434b040794e269
building syzkaller on 2a752b7c5e39457c3c16ef91cf2192a42813c802
testing commit a844dc4c544291470aa69edbe2434b040794e269 with gcc (GCC) 8.1.0
kernel signature: e9610229d94411bf8e70853a6f9edacee35fa0e36767fdea6566db7801ba36ec
all runs: crashed: KASAN: slab-out-of-bounds Read in fbcon_get_font
testing current HEAD a41ba30d9df20fe141c92aacbb56b6b077f19716
testing commit a41ba30d9df20fe141c92aacbb56b6b077f19716 with gcc (GCC) 8.1.0
kernel signature: 2446e75d50f0601f27435aa4eb409485de0d0c21fbbca69c261e2f01ff372e93
all runs: crashed: KASAN: slab-out-of-bounds Read in fbcon_get_font
revisions tested: 2, total time: 25m14.387020363s (build: 17m57.644286958s, test: 6m26.507670506s)
the crash still happens on HEAD
commit msg: Linux 4.14.181
crash: KASAN: slab-out-of-bounds Read in fbcon_get_font
IPv6: ADDRCONF(NETDEV_UP): vxcan1: link is not ready
IPv6: ADDRCONF(NETDEV_CHANGE): vxcan1: link becomes ready
IPv6: ADDRCONF(NETDEV_CHANGE): vxcan0: link becomes ready
8021q: adding VLAN 0 to HW filter on device batadv0
==================================================================
BUG: KASAN: slab-out-of-bounds in memcpy include/linux/string.h:347 [inline]
BUG: KASAN: slab-out-of-bounds in fbcon_get_font+0x21c/0x570 drivers/video/fbdev/core/fbcon.c:2424
Read of size 5 at addr ffff8880a859774c by task syz-executor.1/7522

CPU: 0 PID: 7522 Comm: syz-executor.1 Not tainted 4.14.181-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:17 [inline]
 dump_stack+0xf7/0x13b lib/dump_stack.c:58
 print_address_description.cold.7+0x9/0x1c9 mm/kasan/report.c:252
 kasan_report_error mm/kasan/report.c:351 [inline]
 kasan_report.cold.8+0x11a/0x2d3 mm/kasan/report.c:409
 check_memory_region_inline mm/kasan/kasan.c:260 [inline]
 check_memory_region+0x13e/0x1b0 mm/kasan/kasan.c:267
 memcpy+0x23/0x50 mm/kasan/kasan.c:302
 memcpy include/linux/string.h:347 [inline]
 fbcon_get_font+0x21c/0x570 drivers/video/fbdev/core/fbcon.c:2424
 con_font_get drivers/tty/vt/vt.c:4098 [inline]
 con_font_op+0x75c/0x1020 drivers/tty/vt/vt.c:4249
 do_fontx_ioctl drivers/tty/vt/vt_ioctl.c:265 [inline]
 vt_ioctl+0xfa8/0x21f0 drivers/tty/vt/vt_ioctl.c:945
 tty_ioctl+0x434/0x1260 drivers/tty/tty_io.c:2661
 vfs_ioctl fs/ioctl.c:46 [inline]
 file_ioctl fs/ioctl.c:500 [inline]
 do_vfs_ioctl+0x180/0xfb0 fs/ioctl.c:684
 SYSC_ioctl fs/ioctl.c:701 [inline]
 SyS_ioctl+0x74/0x80 fs/ioctl.c:692
 do_syscall_64+0x1c7/0x5b0 arch/x86/entry/common.c:292
 entry_SYSCALL_64_after_hwframe+0x46/0xbb
RIP: 0033:0x45a909
RSP: 002b:00007ff25b181c78 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 000000000045a909
RDX: 0000000020000140 RSI: 0000000000004b60 RDI: 0000000000000003
RBP: 000000000075bf20 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007ff25b1826d4
R13: 00000000004c7019 R14: 00000000004dd688 R15: 00000000ffffffff

Allocated by task 7513:
 save_stack_trace+0x16/0x20 arch/x86/kernel/stacktrace.c:59
 save_stack+0x43/0xd0 mm/kasan/kasan.c:447
 set_track mm/kasan/kasan.c:459 [inline]
 kasan_kmalloc+0xc7/0xe0 mm/kasan/kasan.c:551
 __do_kmalloc mm/slab.c:3720 [inline]
 __kmalloc+0x15b/0x7b0 mm/slab.c:3729
 kmalloc include/linux/slab.h:493 [inline]
 fbcon_set_font+0x2c9/0x840 drivers/video/fbdev/core/fbcon.c:2621
 con_font_set drivers/tty/vt/vt.c:4182 [inline]
 con_font_op+0xb6f/0x1020 drivers/tty/vt/vt.c:4247
 do_fontx_ioctl drivers/tty/vt/vt_ioctl.c:265 [inline]
 vt_ioctl+0xfa8/0x21f0 drivers/tty/vt/vt_ioctl.c:945
 tty_ioctl+0x434/0x1260 drivers/tty/tty_io.c:2661
 vfs_ioctl fs/ioctl.c:46 [inline]
 file_ioctl fs/ioctl.c:500 [inline]
 do_vfs_ioctl+0x180/0xfb0 fs/ioctl.c:684
 SYSC_ioctl fs/ioctl.c:701 [inline]
 SyS_ioctl+0x74/0x80 fs/ioctl.c:692
 do_syscall_64+0x1c7/0x5b0 arch/x86/entry/common.c:292
 entry_SYSCALL_64_after_hwframe+0x46/0xbb

Freed by task 0:
(stack is not available)

The buggy address belongs to the object at ffff8880a8597340
 which belongs to the cache kmalloc-2048 of size 2048
The buggy address is located 1036 bytes inside of
 2048-byte region [ffff8880a8597340, ffff8880a8597b40)
The buggy address belongs to the page:
page:ffffea0002a16580 count:1 mapcount:0 mapping:ffff8880a8596240 index:0x0 compound_mapcount: 0
flags: 0xfffe0000008100(slab|head)
raw: 00fffe0000008100 ffff8880a8596240 0000000000000000 0000000100000003
raw: ffffea0002121da0 ffffea00021c25a0 ffff8880aa800c40 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff8880a8597600: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
 ffff8880a8597680: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>ffff8880a8597700: 00 00 00 00 00 00 00 00 00 00 fc fc fc fc fc fc
                                                 ^
 ffff8880a8597780: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff8880a8597800: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
==================================================================