• Wanpeng Li's avatar
    KVM: eventfd: fix NULL deref irqbypass consumer · 4f3dbdf4
    Wanpeng Li authored
    Reported syzkaller:
    
        BUG: unable to handle kernel NULL pointer dereference at 0000000000000008
        IP: irq_bypass_unregister_consumer+0x9d/0xb70 [irqbypass]
        PGD 0
    
        Oops: 0002 [#1] SMP
        CPU: 1 PID: 125 Comm: kworker/1:1 Not tainted 4.9.0+ #1
        Workqueue: kvm-irqfd-cleanup irqfd_shutdown [kvm]
        task: ffff9bbe0dfbb900 task.stack: ffffb61802014000
        RIP: 0010:irq_bypass_unregister_consumer+0x9d/0xb70 [irqbypass]
        Call Trace:
         irqfd_shutdown+0x66/0xa0 [kvm]
         process_one_work+0x16b/0x480
         worker_thread+0x4b/0x500
         kthread+0x101/0x140
         ? process_one_work+0x480/0x480
         ? kthread_create_on_node+0x60/0x60
         ret_from_fork+0x25/0x30
        RIP: irq_bypass_unregister_consumer+0x9d/0xb70 [irqbypass] RSP: ffffb61802017e20
        CR2: 0000000000000008
    
    The syzkaller folks reported a NULL pointer dereference that due to
    unregister an consumer which fails registration before. The syzkaller
    creates two VMs w/ an equal eventfd occasionally. So the second VM
    fails to register an irqbypass consumer. It will make irqfd as inactive
    and queue an workqueue work to shutdown irqfd and unregister the irqbypass
    consumer when eventfd is closed. However, the second consumer has been
    initialized though it fails registration. So the token(same as the first
    VM's) is taken to unregister the consumer through the workqueue, the
    consumer of the first VM is found and unregistered, then NULL deref incurred
    in the path of deleting consumer from the consumers list.
    
    This patch fixes it by making irq_bypass_register/unregister_consumer()
    looks for the consumer entry based on consumer pointer itself instead of
    token matching.
    Reported-by: 's avatarDmitry Vyukov <dvyukov@google.com>
    Suggested-by: Alex Williamson's avatarAlex Williamson <alex.williamson@redhat.com>
    Cc: stable@vger.kernel.org
    Cc: Paolo Bonzini <pbonzini@redhat.com>
    Cc: Radim Krčmář <rkrcmar@redhat.com>
    Cc: Dmitry Vyukov <dvyukov@google.com>
    Cc: Alex Williamson <alex.williamson@redhat.com>
    Signed-off-by: 's avatarWanpeng Li <wanpeng.li@hotmail.com>
    Signed-off-by: 's avatarPaolo Bonzini <pbonzini@redhat.com>
    4f3dbdf4
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