bisecting fixing commit since b94de4d19498b454645b72d08a05d32fa9074fb5 building syzkaller on cba33199be220cbf61f7c0c8223d88a25a913d6f testing commit b94de4d19498b454645b72d08a05d32fa9074fb5 with gcc (GCC) 8.1.0 kernel signature: 6b78292a456cb58621f06dd7315d9788fb22aebd537ac4918d81df2b2d3fbf27 all runs: crashed: KASAN: use-after-free Read in kvm_vm_ioctl_unregister_coalesced_mmio testing current HEAD 3207316b3beec7e38e5dbe2f463df0cec71e0b97 testing commit 3207316b3beec7e38e5dbe2f463df0cec71e0b97 with gcc (GCC) 8.1.0 kernel signature: 91de2ef2dd79c5af3ac9efe26783054bb5528a17fc4efdd2a30673cf2f50c0d4 all runs: crashed: KASAN: use-after-free Read in kvm_vm_ioctl_unregister_coalesced_mmio revisions tested: 2, total time: 24m24.580830929s (build: 18m5.861315365s, test: 5m48.745811292s) the crash still happens on HEAD commit msg: Linux 4.19.164 crash: KASAN: use-after-free Read in kvm_vm_ioctl_unregister_coalesced_mmio R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000 R13: 00007ffee802507f R14: 00007f8d707af9c0 R15: 000000000118bf2c kvm: failed to shrink bus, removing it completely ================================================================== BUG: KASAN: use-after-free in kvm_vm_ioctl_unregister_coalesced_mmio+0x1f2/0x2a0 arch/x86/kvm/../../../virt/kvm/coalesced_mmio.c:178 Read of size 8 at addr ffff8881ef334380 by task syz-executor.0/9320 CPU: 0 PID: 9320 Comm: syz-executor.0 Not tainted 4.19.164-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+0x17c/0x22a lib/dump_stack.c:118 print_address_description.cold.6+0x9/0x211 mm/kasan/report.c:256 kasan_report_error mm/kasan/report.c:354 [inline] kasan_report.cold.7+0x242/0x307 mm/kasan/report.c:412 __asan_report_load8_noabort+0x14/0x20 mm/kasan/report.c:433 kvm_vm_ioctl_unregister_coalesced_mmio+0x1f2/0x2a0 arch/x86/kvm/../../../virt/kvm/coalesced_mmio.c:178 kvm_vm_ioctl+0x5ac/0x1770 arch/x86/kvm/../../../virt/kvm/kvm_main.c:3252 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: 0033:0x45deb9 Code: 0d b4 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 db b3 fb ff c3 66 2e 0f 1f 84 00 00 00 00 RSP: 002b:00007f8d707aec78 EFLAGS: 00000246 ORIG_RAX: 0000000000000010 RAX: ffffffffffffffda RBX: 0000000000012740 RCX: 000000000045deb9 RDX: 0000000020000180 RSI: 000000004010ae68 RDI: 0000000000000004 RBP: 00007f8d707aeca0 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000 R13: 00007ffee802507f R14: 00007f8d707af9c0 R15: 000000000118bf2c Allocated by task 9320: save_stack mm/kasan/kasan.c:448 [inline] set_track mm/kasan/kasan.c:460 [inline] kasan_kmalloc.part.1+0x62/0xf0 mm/kasan/kasan.c:553 kasan_kmalloc+0xaf/0xc0 mm/kasan/kasan.c:538 kmem_cache_alloc_trace+0x152/0x3a0 mm/slab.c:3625 kmalloc include/linux/slab.h:515 [inline] kzalloc include/linux/slab.h:709 [inline] kvm_vm_ioctl_register_coalesced_mmio+0x4f/0x320 arch/x86/kvm/../../../virt/kvm/coalesced_mmio.c:146 kvm_vm_ioctl+0xa0e/0x1770 arch/x86/kvm/../../../virt/kvm/kvm_main.c:3243 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 9320: save_stack mm/kasan/kasan.c:448 [inline] set_track mm/kasan/kasan.c:460 [inline] __kasan_slab_free+0x13c/0x220 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 coalesced_mmio_destructor+0x100/0x150 arch/x86/kvm/../../../virt/kvm/coalesced_mmio.c:101 kvm_iodevice_destructor include/kvm/iodev.h:73 [inline] kvm_io_bus_unregister_dev.cold.38+0xbd/0x10e arch/x86/kvm/../../../virt/kvm/kvm_main.c:3875 kvm_vm_ioctl_unregister_coalesced_mmio+0x15b/0x2a0 arch/x86/kvm/../../../virt/kvm/coalesced_mmio.c:180 kvm_vm_ioctl+0x5ac/0x1770 arch/x86/kvm/../../../virt/kvm/kvm_main.c:3252 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 ffff8881ef334380 which belongs to the cache kmalloc-64 of size 64 The buggy address is located 0 bytes inside of 64-byte region [ffff8881ef334380, ffff8881ef3343c0) The buggy address belongs to the page: page:ffffea0007bccd00 count:1 mapcount:0 mapping:ffff8881f6000340 index:0x0 flags: 0x17ff00000000100(slab) raw: 017ff00000000100 ffffea0007ada088 ffffea0007454c48 ffff8881f6000340 raw: 0000000000000000 ffff8881ef334000 0000000100000020 0000000000000000 page dumped because: kasan: bad access detected Memory state around the buggy address: ffff8881ef334280: 00 00 00 00 00 00 00 fc fc fc fc fc fc fc fc fc ffff8881ef334300: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc >ffff8881ef334380: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc ^ ffff8881ef334400: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc ffff8881ef334480: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc ==================================================================