Re: Re: KASAN: use-after-free Write in irq_bypass_register_consumer

[Eric Biggers]

On Sat, Dec 16, 2017 at 04:37:02PM +0800, Lan, Tianyu wrote:
> The root cause is that kvm_irqfd_assign() and kvm_irqfd_deassign() can't
> be run in parallel. Some data structure(e.g, irqfd->consumer) will be
> crashed because irqfd may be freed in deassign path before they are used
> in assign path. The other data maybe used in deassign path before
> initialization. Syzbot test hit such case. Add mutx between
> kvm_irqfd_assign() and kvm_irqfd_deassign() can fix such issue. Will
> send patch to fix it.
> 
> On 12/16/2017 12:53 PM, Tianyu Lan wrote:
> > I reproduced the issue. Will have a look.
> > 
> > -- Best regards Tianyu Lan 2017-12-15 18:14 GMT+08:00 syzbot
> > <bot+7ad82526b98c64c90062275162dacfa48c20dbd3@xxxxxxxxxxxxxxxxxxxxxxxxx>:
> > > syzkaller has found reproducer for the following crash on
> > > 82bcf1def3b5f1251177ad47c44f7e17af039b4b
> > > git://git.cmpxchg.org/linux-mmots.git/master
> > > compiler: gcc (GCC) 7.1.1 20170620
> > > .config is attached
> > > Raw console output is attached.
> > > C reproducer is attached
> > > syzkaller reproducer is attached. Seehttps://goo.gl/kgGztJ
> > > for information about syzkaller reproducers
> > > 
> > > 
> > > ==================================================================
> > > BUG: KASAN: use-after-free in __list_add include/linux/list.h:64 [inline]
> > > BUG: KASAN: use-after-free in list_add include/linux/list.h:79 [inline]
> > > BUG: KASAN: use-after-free in irq_bypass_register_consumer+0x4b4/0x500
> > > virt/lib/irqbypass.c:217
> > > Write of size 8 at addr ffff8801cdf51180 by task syzkaller436086/15031
> > > 
> > > CPU: 1 PID: 15031 Comm: syzkaller436086 Not tainted 4.15.0-rc2-mm1+ #39
> > > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
> > > Google 01/01/2011
> > > Call Trace:
> > >   __dump_stack lib/dump_stack.c:17 [inline]
> > >   dump_stack+0x194/0x257 lib/dump_stack.c:53
> > >   print_address_description+0x73/0x250 mm/kasan/report.c:252
> > >   kasan_report_error mm/kasan/report.c:351 [inline]
> > >   kasan_report+0x25b/0x340 mm/kasan/report.c:409
> > >   __asan_report_store8_noabort+0x17/0x20 mm/kasan/report.c:435
> > >   __list_add include/linux/list.h:64 [inline]
> > >   list_add include/linux/list.h:79 [inline]
> > >   irq_bypass_register_consumer+0x4b4/0x500 virt/lib/irqbypass.c:217
> > >   kvm_irqfd_assign arch/x86/kvm/../../../virt/kvm/eventfd.c:417 [inline]
> > >   kvm_irqfd+0x137f/0x1d50 arch/x86/kvm/../../../virt/kvm/eventfd.c:572
> > >   kvm_vm_ioctl+0x1079/0x1c40 arch/x86/kvm/../../../virt/kvm/kvm_main.c:2992
> > >   vfs_ioctl fs/ioctl.c:46 [inline]
> > >   do_vfs_ioctl+0x1b1/0x1530 fs/ioctl.c:686
> > >   SYSC_ioctl fs/ioctl.c:701 [inline]
> > >   SyS_ioctl+0x8f/0xc0 fs/ioctl.c:692
> > >   entry_SYSCALL_64_fastpath+0x1f/0x96
> > > RIP: 0033:0x44d379
> > > RSP: 002b:00007fc5ff9a9d08 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
> > > RAX: ffffffffffffffda RBX: 00007fc5ff9aa700 RCX: 000000000044d379
> > > RDX: 0000000020080fe0 RSI: 000000004020ae76 RDI: 0000000000000005
> > > RBP: 00000000007ff900 R08: 00007fc5ff9aa700 R09: 00007fc5ff9aa700
> > > R10: 00007fc5ff9aa700 R11: 0000000000000246 R12: 0000000000000000
> > > R13: 00000000007ff8ff R14: 00007fc5ff9aa9c0 R15: 0000000000000000
> > > 
> > > Allocated by task 15031:
> > >   save_stack+0x43/0xd0 mm/kasan/kasan.c:447
> > >   set_track mm/kasan/kasan.c:459 [inline]
> > >   kasan_kmalloc+0xad/0xe0 mm/kasan/kasan.c:551
> > >   kmem_cache_alloc_trace+0x136/0x750 mm/slab.c:3614
> > >   kmalloc include/linux/slab.h:516 [inline]
> > >   kzalloc include/linux/slab.h:705 [inline]
> > >   kvm_irqfd_assign arch/x86/kvm/../../../virt/kvm/eventfd.c:296 [inline]
> > >   kvm_irqfd+0x16c/0x1d50 arch/x86/kvm/../../../virt/kvm/eventfd.c:572
> > >   kvm_vm_ioctl+0x1079/0x1c40 arch/x86/kvm/../../../virt/kvm/kvm_main.c:2992
> > >   vfs_ioctl fs/ioctl.c:46 [inline]
> > >   do_vfs_ioctl+0x1b1/0x1530 fs/ioctl.c:686
> > >   SYSC_ioctl fs/ioctl.c:701 [inline]
> > >   SyS_ioctl+0x8f/0xc0 fs/ioctl.c:692
> > >   entry_SYSCALL_64_fastpath+0x1f/0x96
> > > 
> > > Freed by task 1402:
> > >   save_stack+0x43/0xd0 mm/kasan/kasan.c:447
> > >   set_track mm/kasan/kasan.c:459 [inline]
> > >   kasan_slab_free+0x71/0xc0 mm/kasan/kasan.c:524
> > >   __cache_free mm/slab.c:3492 [inline]
> > >   kfree+0xca/0x250 mm/slab.c:3807
> > >   irqfd_shutdown+0x13c/0x1a0 arch/x86/kvm/../../../virt/kvm/eventfd.c:148
> > >   process_one_work+0xbfd/0x1bc0 kernel/workqueue.c:2113
> > >   worker_thread+0x223/0x1990 kernel/workqueue.c:2247
> > >   kthread+0x37a/0x440 kernel/kthread.c:238
> > >   ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:524
> > > 
> > > The buggy address belongs to the object at ffff8801cdf51000
> > >   which belongs to the cache kmalloc-512 of size 512
> > > The buggy address is located 384 bytes inside of
> > >   512-byte region [ffff8801cdf51000, ffff8801cdf51200)
> > > The buggy address belongs to the page:
> > > page:00000000d08a0d63 count:1 mapcount:0 mapping:00000000d54c7be6 index:0x0
> > > flags: 0x2fffc0000000100(slab)
> > > raw: 02fffc0000000100 ffff8801cdf51000 0000000000000000 0000000100000006
> > > raw: ffffea00073a7660 ffffea000737f3a0 ffff8801dac00940 0000000000000000
> > > page dumped because: kasan: bad access detected
> > > 
> > > Memory state around the buggy address:
> > >   ffff8801cdf51080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> > >   ffff8801cdf51100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> > > > ffff8801cdf51180: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> > >                     ^
> > >   ffff8801cdf51200: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> > >   ffff8801cdf51280: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> > > ==================================================================
> > > 

Tianyu, are you still planning to send a patch for this?  This is still
happening.

- Eric