On 23.03.2017 13:33, Dmitry Vyukov wrote: > Hello, > > I've got the following report while running syzkaller fuzzer on > 093b995e3b55a0ae0670226ddfcb05bfbf0099ae. Note the preceding injected > kmalloc failure, most likely it's the root cause. > > > FAULT_INJECTION: forcing a failure. > name failslab, interval 1, probability 0, space 0, times 0 > CPU: 0 PID: 14650 Comm: syz-executor2 Not tainted 4.11.0-rc3+ #364 > Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011 > Call Trace: > __dump_stack lib/dump_stack.c:16 [inline] > dump_stack+0x1b8/0x28d lib/dump_stack.c:52 > fail_dump lib/fault-inject.c:45 [inline] > should_fail+0x78a/0x870 lib/fault-inject.c:154 > should_failslab+0xec/0x120 mm/failslab.c:31 > slab_pre_alloc_hook mm/slab.h:434 [inline] > slab_alloc mm/slab.c:3394 [inline] > __do_kmalloc mm/slab.c:3734 [inline] > __kmalloc+0x220/0x730 mm/slab.c:3745 > kmalloc include/linux/slab.h:495 [inline] > kvm_io_bus_unregister_dev+0x1a2/0x300 > arch/x86/kvm/../../../virt/kvm/kvm_main.c:3594 > kvm_free_pit+0x58/0x110 arch/x86/kvm/i8254.c:727 > kvm_arch_sync_events+0x35/0x40 arch/x86/kvm/x86.c:8078 > kvm_destroy_vm arch/x86/kvm/../../../virt/kvm/kvm_main.c:727 [inline] > kvm_put_kvm+0x27f/0xa70 arch/x86/kvm/../../../virt/kvm/kvm_main.c:761 > kvm_vm_release+0x42/0x50 arch/x86/kvm/../../../virt/kvm/kvm_main.c:772 > __fput+0x327/0x7f0 fs/file_table.c:209 > ____fput+0x15/0x20 fs/file_table.c:245 > task_work_run+0x1a4/0x270 kernel/task_work.c:116 > tracehook_notify_resume include/linux/tracehook.h:191 [inline] > exit_to_usermode_loop+0x24d/0x2d0 arch/x86/entry/common.c:161 > prepare_exit_to_usermode arch/x86/entry/common.c:191 [inline] > syscall_return_slowpath+0x3bd/0x460 arch/x86/entry/common.c:260 > entry_SYSCALL_64_fastpath+0xc0/0xc2 > RIP: 0033:0x445b79 > RSP: 002b:00007f6e094bc858 EFLAGS: 00000292 ORIG_RAX: 0000000000000021 > RAX: 000000000000001c RBX: 0000000000708000 RCX: 0000000000445b79 > RDX: 0000000000000000 RSI: 000000000000001c RDI: 000000000000001b > RBP: 0000000000000430 R08: 0000000000000000 R09: 0000000000000000 > R10: 0000000000000000 R11: 0000000000000292 R12: 00000000006de4f0 > R13: 000000000000001c R14: 0000000000000000 R15: 000000000000001b > ================================================================== > BUG: KASAN: use-after-free in kvm_io_bus_destroy > include/kvm/iodev.h:72 [inline] at addr ffff88003bfb7d40 > BUG: KASAN: use-after-free in kvm_destroy_vm > arch/x86/kvm/../../../virt/kvm/kvm_main.c:733 [inline] at addr > ffff88003bfb7d40 > BUG: KASAN: use-after-free in kvm_put_kvm+0x932/0xa70 > arch/x86/kvm/../../../virt/kvm/kvm_main.c:761 at addr ffff88003bfb7d40 > Read of size 8 by task syz-executor2/14650 > CPU: 0 PID: 14650 Comm: syz-executor2 Not tainted 4.11.0-rc3+ #364 > Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011 > Call Trace: > __dump_stack lib/dump_stack.c:16 [inline] > dump_stack+0x1b8/0x28d lib/dump_stack.c:52 > kasan_object_err+0x1c/0x70 mm/kasan/report.c:166 > print_address_description mm/kasan/report.c:210 [inline] > kasan_report_error mm/kasan/report.c:294 [inline] > kasan_report.part.2+0x1be/0x480 mm/kasan/report.c:316 > kasan_report mm/kasan/report.c:337 [inline] > __asan_report_load8_noabort+0x29/0x30 mm/kasan/report.c:337 > kvm_io_bus_destroy include/kvm/iodev.h:72 [inline] > kvm_destroy_vm arch/x86/kvm/../../../virt/kvm/kvm_main.c:733 [inline] > kvm_put_kvm+0x932/0xa70 arch/x86/kvm/../../../virt/kvm/kvm_main.c:761 > kvm_vm_release+0x42/0x50 arch/x86/kvm/../../../virt/kvm/kvm_main.c:772 > __fput+0x327/0x7f0 fs/file_table.c:209 > ____fput+0x15/0x20 fs/file_table.c:245 > task_work_run+0x1a4/0x270 kernel/task_work.c:116 > tracehook_notify_resume include/linux/tracehook.h:191 [inline] > exit_to_usermode_loop+0x24d/0x2d0 arch/x86/entry/common.c:161 > prepare_exit_to_usermode arch/x86/entry/common.c:191 [inline] > syscall_return_slowpath+0x3bd/0x460 arch/x86/entry/common.c:260 > entry_SYSCALL_64_fastpath+0xc0/0xc2 > RIP: 0033:0x445b79 > RSP: 002b:00007f6e094bc858 EFLAGS: 00000292 ORIG_RAX: 0000000000000021 > RAX: 000000000000001c RBX: 0000000000708000 RCX: 0000000000445b79 > RDX: 0000000000000000 RSI: 000000000000001c RDI: 000000000000001b > RBP: 0000000000000430 R08: 0000000000000000 R09: 0000000000000000 > R10: 0000000000000000 R11: 0000000000000292 R12: 00000000006de4f0 > R13: 000000000000001c R14: 0000000000000000 R15: 000000000000001b > Object at ffff88003bfb7d40, in cache kmalloc-512 size: 512 > Allocated: > PID = 14650 > save_stack_trace+0x16/0x20 arch/x86/kernel/stacktrace.c:59 > save_stack+0x43/0xd0 mm/kasan/kasan.c:517 > set_track mm/kasan/kasan.c:529 [inline] > kasan_kmalloc+0xbc/0xf0 mm/kasan/kasan.c:620 > kmem_cache_alloc_trace+0x11a/0x720 mm/slab.c:3638 > kmalloc include/linux/slab.h:490 [inline] > kzalloc include/linux/slab.h:663 [inline] > kvm_create_pit+0xc2/0x8b0 arch/x86/kvm/i8254.c:656 > kvm_arch_vm_ioctl+0x1339/0x2190 arch/x86/kvm/x86.c:4058 > kvm_vm_ioctl+0x20f/0x1c60 arch/x86/kvm/../../../virt/kvm/kvm_main.c:3113 > vfs_ioctl fs/ioctl.c:45 [inline] > do_vfs_ioctl+0x1af/0x16d0 fs/ioctl.c:685 > SYSC_ioctl fs/ioctl.c:700 [inline] > SyS_ioctl+0x8f/0xc0 fs/ioctl.c:691 > entry_SYSCALL_64_fastpath+0x1f/0xc2 > Freed: > PID = 14650 > save_stack_trace+0x16/0x20 arch/x86/kernel/stacktrace.c:59 > save_stack+0x43/0xd0 mm/kasan/kasan.c:517 > set_track mm/kasan/kasan.c:529 [inline] > kasan_slab_free+0x81/0xc0 mm/kasan/kasan.c:593 > __cache_free mm/slab.c:3514 [inline] > kfree+0xd7/0x250 mm/slab.c:3831 > kvm_free_pit+0xe0/0x110 arch/x86/kvm/i8254.c:733 > kvm_arch_sync_events+0x35/0x40 arch/x86/kvm/x86.c:8078 > kvm_destroy_vm arch/x86/kvm/../../../virt/kvm/kvm_main.c:727 [inline] > kvm_put_kvm+0x27f/0xa70 arch/x86/kvm/../../../virt/kvm/kvm_main.c:761 > kvm_vm_release+0x42/0x50 arch/x86/kvm/../../../virt/kvm/kvm_main.c:772 > __fput+0x327/0x7f0 fs/file_table.c:209 > ____fput+0x15/0x20 fs/file_table.c:245 > task_work_run+0x1a4/0x270 kernel/task_work.c:116 > tracehook_notify_resume include/linux/tracehook.h:191 [inline] > exit_to_usermode_loop+0x24d/0x2d0 arch/x86/entry/common.c:161 > prepare_exit_to_usermode arch/x86/entry/common.c:191 [inline] > syscall_return_slowpath+0x3bd/0x460 arch/x86/entry/common.c:260 > entry_SYSCALL_64_fastpath+0xc0/0xc2 > Memory state around the buggy address: > ffff88003bfb7c00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 > ffff88003bfb7c80: 00 00 00 00 00 00 00 fc fc fc fc fc fc fc fc fc >> ffff88003bfb7d00: fc fc fc fc fc fc fc fc fb fb fb fb fb fb fb fb > ^ > ffff88003bfb7d80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb > ffff88003bfb7e00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb > ================================================================== >
Looks like nobody is prepared to see kvm_io_bus_unregister_dev() fail. kvm_free_pit() silently goes ahead and and zappes itself. Actually, I think nobody even takes care if kvm_io_bus_unregister_dev() fails, so this is a more general problem. It should never fail. No caller can handle it. Will look into this! zyzkaller is magic, thanks Dimitry. -- Thanks, David
