[PATCH 1/2] KVM: Fix NULL-ptr defer after kvm_create_vm fails

[Wanpeng Li]

From: Wanpeng Li <wanpengli@xxxxxxxxxxx>

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 9121923c457d ("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 deferenced by kvm_coalesced_mmio_init(), this patch 
fixes it.

syz repro: https://syzkaller.appspot.com/x/repro.syz?x=13509b84e00000

Reported-by: syzbot+89a8060879fa0bd2db4f@xxxxxxxxxxxxxxxxxxxxxxxxx
Fixes: 9121923c457d ("kvm: Allocate memslots and buses before calling kvm_arch_init_vm") 
Cc: Jim Mattson <jmattson@xxxxxxxxxx>
Signed-off-by: Wanpeng Li <wanpengli@xxxxxxxxxxx>
---
 virt/kvm/kvm_main.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index d6f0696..8c272eb 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -675,6 +675,7 @@ static struct kvm *kvm_create_vm(unsigned long type)
 	INIT_HLIST_HEAD(&kvm->irq_ack_notifier_list);
 #endif
 
+	r = -ENOMEM;
 	if (init_srcu_struct(&kvm->srcu))
 		goto out_err_no_srcu;
 	if (init_srcu_struct(&kvm->irq_srcu))
-- 
2.7.4