• Paolo Bonzini's avatar
    KVM: Fix NULL-ptr deref after kvm_create_vm fails · 8a44119a
    Paolo Bonzini authored
    Reported by syzkaller:
    
        kasan: CONFIG_KASAN_INLINE enabled
        kasan: GPF could be caused by NULL-ptr deref or user memory access
        general protection fault: 0000 [#1] PREEMPT SMP KASAN
        CPU: 0 PID: 14727 Comm: syz-executor.3 Not tainted 5.4.0-rc4+ #0
        RIP: 0010:kvm_coalesced_mmio_init+0x5d/0x110 arch/x86/kvm/../../../virt/kvm/coalesced_mmio.c:121
        Call Trace:
         kvm_dev_ioctl_create_vm arch/x86/kvm/../../../virt/kvm/kvm_main.c:3446 [inline]
         kvm_dev_ioctl+0x781/0x1490 arch/x86/kvm/../../../virt/kvm/kvm_main.c:3494
         vfs_ioctl fs/ioctl.c:46 [inline]
         file_ioctl fs/ioctl.c:509 [inline]
         do_vfs_ioctl+0x196/0x1150 fs/ioctl.c:696
         ksys_ioctl+0x62/0x90 fs/ioctl.c:713
         __do_sys_ioctl fs/ioctl.c:720 [inline]
         __se_sys_ioctl fs/ioctl.c:718 [inline]
         __x64_sys_ioctl+0x6e/0xb0 fs/ioctl.c:718
         do_syscall_64+0xca/0x5d0 arch/x86/entry/common.c:290
         entry_SYSCALL_64_after_hwframe+0x49/0xbe
    
    Commit 9121923c ("kvm: Allocate memslots and buses before calling kvm_arch_init_vm")
    moves memslots and buses allocations around, however, if kvm->srcu/irq_srcu fails
    initialization, NULL will be returned instead of error code, NULL will not be intercepted
    in kvm_dev_ioctl_create_vm() and be dereferenced by kvm_coalesced_mmio_init(), this patch
    fixes it.
    
    Moving the initialization is required anyway to avoid an incorrect synchronize_srcu that
    was also reported by syzkaller:
    
     wait_for_completion+0x29c/0x440 kernel/sched/completion.c:136
     __synchronize_srcu+0x197/0x250 kernel/rcu/srcutree.c:921
     synchronize_srcu_expedited kernel/rcu/srcutree.c:946 [inline]
     synchronize_srcu+0x239/0x3e8 kernel/rcu/srcutree.c:997
     kvm_page_track_unregister_notifier+0xe7/0x130 arch/x86/kvm/page_track.c:212
     kvm_mmu_uninit_vm+0x1e/0x30 arch/x86/kvm/mmu.c:5828
     kvm_arch_destroy_vm+0x4a2/0x5f0 arch/x86/kvm/x86.c:9579
     kvm_create_vm arch/x86/kvm/../../../virt/kvm/kvm_main.c:702 [inline]
    
    so do it.
    
    Reported-by: syzbot+89a8060879fa0bd2db4f@syzkaller.appspotmail.com
    Reported-by: syzbot+e27e7027eb2b80e44225@syzkaller.appspotmail.com
    Fixes: 9121923c ("kvm: Allocate memslots and buses before calling kvm_arch_init_vm")
    Cc: Jim Mattson <jmattson@google.com>
    Cc: Wanpeng Li <wanpengli@tencent.com>
    Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
    8a44119a
kvm_main.c 102 KB