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BUG: KASAN: use-after-free in fbcon_cursor+0x4ef/0x660 drivers/video/fbdev/core/fbcon.c:1380
Read of size 2 at addr ffff8880a8f9938c by task syz-executor.0/9418

CPU: 0 PID: 9418 Comm: syz-executor.0 Not tainted 5.5.0-rc2-next-20191220-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+0xd4/0x30b 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_load2_noabort+0x14/0x20 mm/kasan/generic_report.c:133
 fbcon_cursor+0x4ef/0x660 drivers/video/fbdev/core/fbcon.c:1380
 fbcon_scrolldelta+0x679/0x1220 drivers/video/fbdev/core/fbcon.c:2877
 fbcon_set_origin+0x43/0x50 drivers/video/fbdev/core/fbcon.c:2928
 set_origin+0xf3/0x400 drivers/tty/vt/vt.c:919
 vc_do_resize+0xacc/0x1460 drivers/tty/vt/vt.c:1264
 vc_resize+0x4d/0x60 drivers/tty/vt/vt.c:1304
 vt_ioctl+0x14bb/0x26d0 drivers/tty/vt/vt_ioctl.c:840
 tty_ioctl+0xa37/0x14f0 drivers/tty/tty_io.c:2660
 vfs_ioctl fs/ioctl.c:47 [inline]
 ksys_ioctl+0x123/0x180 fs/ioctl.c:747
 __do_sys_ioctl fs/ioctl.c:756 [inline]
 __se_sys_ioctl fs/ioctl.c:754 [inline]
 __x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:754
 do_syscall_64+0xfa/0x790 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x45a919
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:00007fde31333c78 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 000000000045a919
RDX: 0000000020000000 RSI: 0000000000005609 RDI: 0000000000000003
RBP: 000000000075bf20 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007fde313346d4
R13: 00000000004c6fec R14: 00000000004dd790 R15: 00000000ffffffff

Allocated by task 9418:
 save_stack+0x23/0x90 mm/kasan/common.c:72
 set_track mm/kasan/common.c:80 [inline]
 __kasan_kmalloc mm/kasan/common.c:513 [inline]
 __kasan_kmalloc.constprop.0+0xcf/0xe0 mm/kasan/common.c:486
 kasan_kmalloc+0x9/0x10 mm/kasan/common.c:527
 __do_kmalloc mm/slab.c:3656 [inline]
 __kmalloc+0x163/0x770 mm/slab.c:3665
 kmalloc include/linux/slab.h:560 [inline]
 kzalloc include/linux/slab.h:669 [inline]
 vc_do_resize+0x262/0x1460 drivers/tty/vt/vt.c:1187
 vc_resize+0x4d/0x60 drivers/tty/vt/vt.c:1304
 vt_ioctl+0x14bb/0x26d0 drivers/tty/vt/vt_ioctl.c:840
 tty_ioctl+0xa37/0x14f0 drivers/tty/tty_io.c:2660
 vfs_ioctl fs/ioctl.c:47 [inline]
 ksys_ioctl+0x123/0x180 fs/ioctl.c:747
 __do_sys_ioctl fs/ioctl.c:756 [inline]
 __se_sys_ioctl fs/ioctl.c:754 [inline]
 __x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:754
 do_syscall_64+0xfa/0x790 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x49/0xbe

Freed by task 9418:
 save_stack+0x23/0x90 mm/kasan/common.c:72
 set_track mm/kasan/common.c:80 [inline]
 kasan_set_free_info mm/kasan/common.c:335 [inline]
 __kasan_slab_free+0x102/0x150 mm/kasan/common.c:474
 kasan_slab_free+0xe/0x10 mm/kasan/common.c:483
 __cache_free mm/slab.c:3426 [inline]
 kfree+0x10a/0x2c0 mm/slab.c:3757
 vc_do_resize+0xa69/0x1460 drivers/tty/vt/vt.c:1261
 vc_resize+0x4d/0x60 drivers/tty/vt/vt.c:1304
 vt_ioctl+0x14bb/0x26d0 drivers/tty/vt/vt_ioctl.c:840
 tty_ioctl+0xa37/0x14f0 drivers/tty/tty_io.c:2660
 vfs_ioctl fs/ioctl.c:47 [inline]
 ksys_ioctl+0x123/0x180 fs/ioctl.c:747
 __do_sys_ioctl fs/ioctl.c:756 [inline]
 __se_sys_ioctl fs/ioctl.c:754 [inline]
 __x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:754
 do_syscall_64+0xfa/0x790 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x49/0xbe

The buggy address belongs to the object at ffff8880a8f99380
 which belongs to the cache kmalloc-32 of size 32
The buggy address is located 12 bytes inside of
 32-byte region [ffff8880a8f99380, ffff8880a8f993a0)
The buggy address belongs to the page:
page:ffffea0002a3e640 refcount:1 mapcount:0 mapping:ffff8880aa4001c0 index:0xffff8880a8f99fc1
raw: 00fffe0000000200 ffffea0002a4d6c8 ffffea00028d4e48 ffff8880aa4001c0
raw: ffff8880a8f99fc1 ffff8880a8f99000 000000010000003f 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff8880a8f99280: fb fb fb fb fc fc fc fc fb fb fb fb fc fc fc fc
 ffff8880a8f99300: fb fb fb fb fc fc fc fc fb fb fb fb fc fc fc fc
>ffff8880a8f99380: fb fb fb fb fc fc fc fc fb fb fb fb fc fc fc fc
                      ^
 ffff8880a8f99400: fb fb fb fb fc fc fc fc fb fb fb fb fc fc fc fc
 ffff8880a8f99480: fb fb fb fb fc fc fc fc 00 00 00 00 fc fc fc fc
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