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Subjectkvm: use-after-free in process_srcu
Hello,

I am getting the following use-after-free reports while running
syzkaller fuzzer.
On commit 318c8932ddec5c1c26a4af0f3c053784841c598e (Dec 7).
Unfortunately it is not reproducible, but all reports look sane and
very similar, so I would assume that it is some hard to trigger race.
In all cases the use-after-free offset within struct kvm is 344 bytes.
This points to srcu field, which starts at 208 with size 360 (I have
some debug configs enabled).


BUG: KASAN: use-after-free in process_srcu+0x27a/0x280 at addr ffff88005e29a418
Read of size 8 by task kworker/3:1/1496
CPU: 3 PID: 1496 Comm: kworker/3:1 Not tainted 4.9.0-rc8+ #78
Hardware name: Google Google/Google, BIOS Google 01/01/2011
Workqueue: events_power_efficient process_srcu
ffff88006b1df3a0 ffffffff8348fb59 ffffffff00000003 1ffff1000d63be07
ffffed000d63bdff 0000000041b58ab3 ffffffff8957cf20 ffffffff8348f86b
ffff8800668dc440 ffffffff8816c000 1ffff1000d63be18 dffffc0000000000
Call Trace:
[< inline >] __dump_stack lib/dump_stack.c:15
[<ffffffff8348fb59>] dump_stack+0x2ee/0x3f5 lib/dump_stack.c:51
[<ffffffff819f1c21>] kasan_object_err+0x21/0x70 mm/kasan/report.c:163
[< inline >] print_address_description mm/kasan/report.c:201
[< inline >] kasan_report_error mm/kasan/report.c:285
[<ffffffff819f1ec1>] kasan_report+0x1a1/0x440 mm/kasan/report.c:305
[<ffffffff819f21d9>] __asan_report_load8_noabort+0x19/0x20
mm/kasan/report.c:331
[< inline >] rcu_batch_empty kernel/rcu/srcu.c:64
[< inline >] rcu_batch_dequeue kernel/rcu/srcu.c:75
[< inline >] srcu_invoke_callbacks kernel/rcu/srcu.c:624
[<ffffffff815ba91a>] process_srcu+0x27a/0x280 kernel/rcu/srcu.c:672
[<ffffffff814731c0>] process_one_work+0xb40/0x1ba0 kernel/workqueue.c:2096
[<ffffffff81474434>] worker_thread+0x214/0x18a0 kernel/workqueue.c:2230
[<ffffffff8148a058>] kthread+0x328/0x3e0 kernel/kthread.c:209
[<ffffffff8816c61a>] ret_from_fork+0x2a/0x40 arch/x86/entry/entry_64.S:433
Object at ffff88005e29a2c0, in cache kmalloc-16384 size: 16384
Allocated:
PID = 13066
[ 376.024345] [<ffffffff81270fdb>] save_stack_trace+0x1b/0x20
arch/x86/kernel/stacktrace.c:57
[ 376.024345] [<ffffffff819f0ea3>] save_stack+0x43/0xd0 mm/kasan/kasan.c:495
[ 376.024345] [< inline >] set_track mm/kasan/kasan.c:507
[ 376.024345] [<ffffffff819f116d>] kasan_kmalloc+0xad/0xe0
mm/kasan/kasan.c:598
[ 376.024345] [<ffffffff819ed4ec>]
kmem_cache_alloc_trace+0x12c/0x710 mm/slab.c:3635
[ 376.024345] [< inline >] kvm_arch_alloc_vm include/linux/slab.h:490
[ 376.024345] [< inline >] kvm_create_vm
arch/x86/kvm/../../../virt/kvm/kvm_main.c:610
[ 376.024345] [< inline >] kvm_dev_ioctl_create_vm
arch/x86/kvm/../../../virt/kvm/kvm_main.c:3164
[ 376.024345] [<ffffffff810789d5>] kvm_dev_ioctl+0x1b5/0x1100
arch/x86/kvm/../../../virt/kvm/kvm_main.c:3208
[ 376.024345] [< inline >] vfs_ioctl fs/ioctl.c:43
[ 376.024345] [<ffffffff81abdf24>] do_vfs_ioctl+0x1c4/0x1630 fs/ioctl.c:679
[ 376.024345] [< inline >] SYSC_ioctl fs/ioctl.c:694
[ 376.024345] [<ffffffff81abf424>] SyS_ioctl+0x94/0xc0 fs/ioctl.c:685
[ 376.024345] [<ffffffff8816c385>] entry_SYSCALL_64_fastpath+0x23/0xc6
Freed:
PID = 13064
[ 376.024345] [<ffffffff81270fdb>] save_stack_trace+0x1b/0x20
arch/x86/kernel/stacktrace.c:57
[ 376.024345] [<ffffffff819f0ea3>] save_stack+0x43/0xd0 mm/kasan/kasan.c:495
[ 376.024345] [< inline >] set_track mm/kasan/kasan.c:507
[ 376.024345] [<ffffffff819f17c2>] kasan_slab_free+0x72/0xc0
mm/kasan/kasan.c:571
[ 376.024345] [< inline >] __cache_free mm/slab.c:3511
[ 376.024345] [<ffffffff819ef3e8>] kfree+0xc8/0x2a0 mm/slab.c:3828
[ 376.024345] [< inline >] kvm_arch_free_vm
include/linux/kvm_host.h:774
[ 376.024345] [< inline >] kvm_destroy_vm
arch/x86/kvm/../../../virt/kvm/kvm_main.c:739
[ 376.024345] [<ffffffff8106fcd9>] kvm_put_kvm+0x489/0x5f0
arch/x86/kvm/../../../virt/kvm/kvm_main.c:754
[ 376.024345] [<ffffffff8106ff97>] kvm_vm_release+0x47/0x60
arch/x86/kvm/../../../virt/kvm/kvm_main.c:765
[ 376.024345] [<ffffffff81a77f7e>] __fput+0x34e/0x910 fs/file_table.c:208
[ 376.024345] [<ffffffff81a785ca>] ____fput+0x1a/0x20 fs/file_table.c:244
[ 376.024345] [<ffffffff81483c20>] task_work_run+0x1a0/0x280
kernel/task_work.c:116
[ 376.024345] [< inline >] exit_task_work include/linux/task_work.h:21
[ 376.024345] [<ffffffff814129e2>] do_exit+0x1842/0x2650 kernel/exit.c:828
[ 376.024345] [<ffffffff814139ae>] do_group_exit+0x14e/0x420 kernel/exit.c:932
[ 376.024345] [<ffffffff81442b43>] get_signal+0x663/0x1880
kernel/signal.c:2307
[ 376.024345] [<ffffffff81239b45>] do_signal+0xc5/0x2190
arch/x86/kernel/signal.c:807
[ 376.024345] [<ffffffff8100666a>] exit_to_usermode_loop+0x1ea/0x2d0
arch/x86/entry/common.c:156
[ 376.024345] [< inline >] prepare_exit_to_usermode
arch/x86/entry/common.c:190
[ 376.024345] [<ffffffff81009693>]
syscall_return_slowpath+0x4d3/0x570 arch/x86/entry/common.c:259
[ 376.024345] [<ffffffff8816c426>] entry_SYSCALL_64_fastpath+0xc4/0xc6
Memory state around the buggy address:
ffff88005e29a300: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff88005e29a380: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff88005e29a400: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff88005e29a480: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff88005e29a500: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================

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