bisecting fixing commit since 312017a460d5ea31d646e7148e400e13db799ddc building syzkaller on eef6e5808d6507716d331b9eff67fdd991be891a testing commit 312017a460d5ea31d646e7148e400e13db799ddc with gcc (GCC) 8.1.0 kernel signature: ef14c6aa067a94f40e8307c379da52982719f162 all runs: crashed: KASAN: use-after-free Read in fbcon_cursor testing current HEAD dcd888983542055210f5e68f1b1f1f8fe11a369a testing commit dcd888983542055210f5e68f1b1f1f8fe11a369a with gcc (GCC) 8.1.0 kernel signature: 29db6f632f0e55bfe2daada9c8b32059b5f0d71a all runs: crashed: KASAN: use-after-free Read in fbcon_cursor revisions tested: 2, total time: 25m14.444627801s (build: 17m35.219168308s, test: 7m12.9320003s) the crash still happens on HEAD commit msg: Linux 4.19.95 crash: KASAN: use-after-free Read in fbcon_cursor IPv6: ADDRCONF(NETDEV_CHANGE): vxcan1: link becomes ready IPv6: ADDRCONF(NETDEV_CHANGE): vxcan0: link becomes ready ================================================================== BUG: KASAN: use-after-free in fbcon_cursor+0x583/0x6c0 drivers/video/fbdev/core/fbcon.c:1347 Read of size 2 at addr ffff8880804f148c by task syz-executor.1/9701 CPU: 0 PID: 9701 Comm: syz-executor.1 Not tainted 4.19.95-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 print_address_description.cold.8+0x9/0x1ff mm/kasan/report.c:256 kasan_report_error mm/kasan/report.c:354 [inline] kasan_report.cold.9+0x242/0x309 mm/kasan/report.c:412 __asan_report_load2_noabort+0x14/0x20 mm/kasan/report.c:431 fbcon_cursor+0x583/0x6c0 drivers/video/fbdev/core/fbcon.c:1347 fbcon_scrolldelta+0x521/0xff0 drivers/video/fbdev/core/fbcon.c:2855 fbcon_set_origin+0x16/0x20 drivers/video/fbdev/core/fbcon.c:2906 set_origin+0x31c/0x400 drivers/tty/vt/vt.c:919 vc_do_resize+0x90b/0x1330 drivers/tty/vt/vt.c:1267 vc_resize+0x3d/0x60 drivers/tty/vt/vt.c:1307 vt_ioctl+0x36e/0x2130 drivers/tty/vt/vt_ioctl.c:840 tty_ioctl+0x452/0x1290 drivers/tty/tty_io.c:2669 vfs_ioctl fs/ioctl.c:46 [inline] file_ioctl fs/ioctl.c:501 [inline] do_vfs_ioctl+0x196/0x10c0 fs/ioctl.c:688 ksys_ioctl+0x62/0x90 fs/ioctl.c:705 __do_sys_ioctl fs/ioctl.c:712 [inline] __se_sys_ioctl fs/ioctl.c:710 [inline] __x64_sys_ioctl+0x6e/0xb0 fs/ioctl.c:710 do_syscall_64+0xd0/0x4e0 arch/x86/entry/common.c:293 entry_SYSCALL_64_after_hwframe+0x49/0xbe RIP: 0033:0x45a909 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:00007fd18078ac78 EFLAGS: 00000246 ORIG_RAX: 0000000000000010 RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 000000000045a909 RDX: 0000000020000000 RSI: 0000000000005609 RDI: 0000000000000003 RBP: 000000000075bf20 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 00007fd18078b6d4 R13: 00000000004c7009 R14: 00000000004dd670 R15: 00000000ffffffff Allocated by task 9713: save_stack+0x43/0xd0 mm/kasan/kasan.c:448 set_track mm/kasan/kasan.c:460 [inline] kasan_kmalloc+0xc7/0xe0 mm/kasan/kasan.c:553 __do_kmalloc mm/slab.c:3727 [inline] __kmalloc+0x15b/0x770 mm/slab.c:3736 kmalloc include/linux/slab.h:520 [inline] kzalloc include/linux/slab.h:709 [inline] vc_do_resize+0x1de/0x1330 drivers/tty/vt/vt.c:1190 vc_resize+0x3d/0x60 drivers/tty/vt/vt.c:1307 vt_ioctl+0x36e/0x2130 drivers/tty/vt/vt_ioctl.c:840 tty_ioctl+0x452/0x1290 drivers/tty/tty_io.c:2669 vfs_ioctl fs/ioctl.c:46 [inline] file_ioctl fs/ioctl.c:501 [inline] do_vfs_ioctl+0x196/0x10c0 fs/ioctl.c:688 ksys_ioctl+0x62/0x90 fs/ioctl.c:705 __do_sys_ioctl fs/ioctl.c:712 [inline] __se_sys_ioctl fs/ioctl.c:710 [inline] __x64_sys_ioctl+0x6e/0xb0 fs/ioctl.c:710 do_syscall_64+0xd0/0x4e0 arch/x86/entry/common.c:293 entry_SYSCALL_64_after_hwframe+0x49/0xbe Freed by task 9701: save_stack+0x43/0xd0 mm/kasan/kasan.c:448 set_track mm/kasan/kasan.c:460 [inline] __kasan_slab_free+0x102/0x150 mm/kasan/kasan.c:521 kasan_slab_free+0xe/0x10 mm/kasan/kasan.c:528 __cache_free mm/slab.c:3503 [inline] kfree+0xcf/0x220 mm/slab.c:3822 vc_do_resize+0x8a8/0x1330 drivers/tty/vt/vt.c:1264 vc_resize+0x3d/0x60 drivers/tty/vt/vt.c:1307 vt_ioctl+0x36e/0x2130 drivers/tty/vt/vt_ioctl.c:840 tty_ioctl+0x452/0x1290 drivers/tty/tty_io.c:2669 vfs_ioctl fs/ioctl.c:46 [inline] file_ioctl fs/ioctl.c:501 [inline] do_vfs_ioctl+0x196/0x10c0 fs/ioctl.c:688 ksys_ioctl+0x62/0x90 fs/ioctl.c:705 __do_sys_ioctl fs/ioctl.c:712 [inline] __se_sys_ioctl fs/ioctl.c:710 [inline] __x64_sys_ioctl+0x6e/0xb0 fs/ioctl.c:710 do_syscall_64+0xd0/0x4e0 arch/x86/entry/common.c:293 entry_SYSCALL_64_after_hwframe+0x49/0xbe The buggy address belongs to the object at ffff8880804f1480 which belongs to the cache kmalloc-32 of size 32 The buggy address is located 12 bytes inside of 32-byte region [ffff8880804f1480, ffff8880804f14a0) The buggy address belongs to the page: page:ffffea0002013c40 count:1 mapcount:0 mapping:ffff88812c29c1c0 index:0xffff8880804f1fc1 flags: 0xfffe0000000100(slab) raw: 00fffe0000000100 ffffea0002274e48 ffffea00027b3e48 ffff88812c29c1c0 raw: ffff8880804f1fc1 ffff8880804f1000 000000010000003c 0000000000000000 page dumped because: kasan: bad access detected Memory state around the buggy address: ffff8880804f1380: 00 00 01 fc fc fc fc fc fb fb fb fb fc fc fc fc ffff8880804f1400: fb fb fb fb fc fc fc fc fb fb fb fb fc fc fc fc >ffff8880804f1480: fb fb fb fb fc fc fc fc fb fb fb fb fc fc fc fc ^ ffff8880804f1500: fb fb fb fb fc fc fc fc fb fb fb fb fc fc fc fc ffff8880804f1580: fb fb fb fb fc fc fc fc fb fb fb fb fc fc fc fc ==================================================================