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SubjectKASAN: use-after-free Read in irq_bypass_unregister_consumer
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Hello,

syzbot found the following crash on:

HEAD commit: 0b449a441dac Merge tag 'dmaengine-fix-4.17-rc6' of git://g..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=16a44b37800000
kernel config: https://syzkaller.appspot.com/x/.config?x=f3b4e30da84ec1ed
dashboard link: https://syzkaller.appspot.com/bug?extid=37364ced0d0b0fdf115c
compiler: gcc (GCC) 8.0.1 20180413 (experimental)
syzkaller repro:https://syzkaller.appspot.com/x/repro.syz?x=1120eb37800000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=13f1227b800000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+37364ced0d0b0fdf115c@syzkaller.appspotmail.com

random: sshd: uninitialized urandom read (32 bytes read)
random: sshd: uninitialized urandom read (32 bytes read)
random: sshd: uninitialized urandom read (32 bytes read)
IPVS: ftp: loaded support on port[0] = 21
==================================================================
BUG: KASAN: use-after-free in irq_bypass_unregister_consumer+0x3cd/0x4a0
virt/lib/irqbypass.c:247
Read of size 8 at addr ffff8801adf2a168 by task kworker/0:1/24

CPU: 0 PID: 24 Comm: kworker/0:1 Not tainted 4.17.0-rc5+ #59
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
Workqueue: kvm-irqfd-cleanup irqfd_shutdown
Call Trace:
__dump_stack lib/dump_stack.c:77 [inline]
dump_stack+0x1b9/0x294 lib/dump_stack.c:113
print_address_description+0x6c/0x20b mm/kasan/report.c:256
kasan_report_error mm/kasan/report.c:354 [inline]
kasan_report.cold.7+0x242/0x2fe mm/kasan/report.c:412
__asan_report_load8_noabort+0x14/0x20 mm/kasan/report.c:433
irq_bypass_unregister_consumer+0x3cd/0x4a0 virt/lib/irqbypass.c:247
irqfd_shutdown+0x112/0x1a0 arch/x86/kvm/../../../virt/kvm/eventfd.c:145
process_one_work+0xc1e/0x1b50 kernel/workqueue.c:2145
worker_thread+0x1cc/0x1440 kernel/workqueue.c:2279
kthread+0x345/0x410 kernel/kthread.c:240
ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:412

Allocated by task 4534:
save_stack+0x43/0xd0 mm/kasan/kasan.c:448
set_track mm/kasan/kasan.c:460 [inline]
kasan_kmalloc+0xc4/0xe0 mm/kasan/kasan.c:553
kmem_cache_alloc_trace+0x152/0x780 mm/slab.c:3620
kmalloc include/linux/slab.h:512 [inline]
kzalloc include/linux/slab.h:701 [inline]
kvm_irqfd_assign arch/x86/kvm/../../../virt/kvm/eventfd.c:296 [inline]
kvm_irqfd+0x187/0x1ec0 arch/x86/kvm/../../../virt/kvm/eventfd.c:572
kvm_vm_ioctl+0xf84/0x1d90 arch/x86/kvm/../../../virt/kvm/kvm_main.c:2997
vfs_ioctl fs/ioctl.c:46 [inline]
file_ioctl fs/ioctl.c:500 [inline]
do_vfs_ioctl+0x1cf/0x16a0 fs/ioctl.c:684
ksys_ioctl+0xa9/0xd0 fs/ioctl.c:701
__do_sys_ioctl fs/ioctl.c:708 [inline]
__se_sys_ioctl fs/ioctl.c:706 [inline]
__x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:706
do_syscall_64+0x1b1/0x800 arch/x86/entry/common.c:287
entry_SYSCALL_64_after_hwframe+0x49/0xbe

Freed by task 24:
save_stack+0x43/0xd0 mm/kasan/kasan.c:448
set_track mm/kasan/kasan.c:460 [inline]
__kasan_slab_free+0x11a/0x170 mm/kasan/kasan.c:521
kasan_slab_free+0xe/0x10 mm/kasan/kasan.c:528
__cache_free mm/slab.c:3498 [inline]
kfree+0xd9/0x260 mm/slab.c:3813
irqfd_shutdown+0x13a/0x1a0 arch/x86/kvm/../../../virt/kvm/eventfd.c:148
process_one_work+0xc1e/0x1b50 kernel/workqueue.c:2145
worker_thread+0x1cc/0x1440 kernel/workqueue.c:2279
kthread+0x345/0x410 kernel/kthread.c:240
ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:412

The buggy address belongs to the object at ffff8801adf2a000
which belongs to the cache kmalloc-512 of size 512
The buggy address is located 360 bytes inside of
512-byte region [ffff8801adf2a000, ffff8801adf2a200)
The buggy address belongs to the page:
page:ffffea0006b7ca80 count:1 mapcount:0 mapping:ffff8801adf2a000 index:0x0
flags: 0x2fffc0000000100(slab)
raw: 02fffc0000000100 ffff8801adf2a000 0000000000000000 0000000100000006
raw: ffffea0007647a20 ffffea0006b45ba0 ffff8801da800940 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff8801adf2a000: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff8801adf2a080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> ffff8801adf2a100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff8801adf2a180: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff8801adf2a200: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
==================================================================


---
This bug is generated by a bot. It may contain errors.
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