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authorPaolo Bonzini <pbonzini@redhat.com>2016-06-01 14:09:24 +0200
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2019-07-21 09:07:16 +0200
commitc02686acab234a36aeb678a040d8aee0c4a07845 (patch)
tree8f2108c9da0f29f112c8dcbae9ad243d7524b092
parent970871c643fc8ba2b0eabe740303c8a155b35e22 (diff)
KVM: x86: protect KVM_CREATE_PIT/KVM_CREATE_PIT2 with kvm->lock
commit 250715a6171a076748be8ab88b274e72f0cfb435 upstream. The syzkaller folks reported a NULL pointer dereference that seems to be cause by a race between KVM_CREATE_IRQCHIP and KVM_CREATE_PIT2. The former takes kvm->lock (except when registering the devices, which needs kvm->slots_lock); the latter takes kvm->slots_lock only. Change KVM_CREATE_PIT2 to follow the same model as KVM_CREATE_IRQCHIP. Testcase: #include <pthread.h> #include <linux/kvm.h> #include <fcntl.h> #include <sys/ioctl.h> #include <stdint.h> #include <string.h> #include <stdlib.h> #include <sys/syscall.h> #include <unistd.h> long r[23]; void* thr1(void* arg) { struct kvm_pit_config pitcfg = { .flags = 4 }; switch ((long)arg) { case 0: r[2] = open("/dev/kvm", O_RDONLY|O_ASYNC); break; case 1: r[3] = ioctl(r[2], KVM_CREATE_VM, 0); break; case 2: r[4] = ioctl(r[3], KVM_CREATE_IRQCHIP, 0); break; case 3: r[22] = ioctl(r[3], KVM_CREATE_PIT2, &pitcfg); break; } return 0; } int main(int argc, char **argv) { long i; pthread_t th[4]; memset(r, -1, sizeof(r)); for (i = 0; i < 4; i++) { pthread_create(&th[i], 0, thr, (void*)i); if (argc > 1 && rand()%2) usleep(rand()%1000); } usleep(20000); return 0; } Reported-by: Dmitry Vyukov <dvyukov@google.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> Signed-off-by: Radim Krčmář <rkrcmar@redhat.com> Signed-off-by: Zubin Mithra <zsm@google.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
-rw-r--r--arch/x86/kvm/i8254.c5
-rw-r--r--arch/x86/kvm/x86.c4
2 files changed, 5 insertions, 4 deletions
diff --git a/arch/x86/kvm/i8254.c b/arch/x86/kvm/i8254.c
index ab5318727579..ef56d70d1026 100644
--- a/arch/x86/kvm/i8254.c
+++ b/arch/x86/kvm/i8254.c
@@ -678,7 +678,6 @@ static const struct kvm_io_device_ops speaker_dev_ops = {
.write = speaker_ioport_write,
};
-/* Caller must hold slots_lock */
struct kvm_pit *kvm_create_pit(struct kvm *kvm, u32 flags)
{
struct kvm_pit *pit;
@@ -733,6 +732,7 @@ struct kvm_pit *kvm_create_pit(struct kvm *kvm, u32 flags)
pit->mask_notifier.func = pit_mask_notifer;
kvm_register_irq_mask_notifier(kvm, 0, &pit->mask_notifier);
+ mutex_lock(&kvm->slots_lock);
kvm_iodevice_init(&pit->dev, &pit_dev_ops);
ret = kvm_io_bus_register_dev(kvm, KVM_PIO_BUS, KVM_PIT_BASE_ADDRESS,
KVM_PIT_MEM_LENGTH, &pit->dev);
@@ -747,13 +747,14 @@ struct kvm_pit *kvm_create_pit(struct kvm *kvm, u32 flags)
if (ret < 0)
goto fail_unregister;
}
+ mutex_unlock(&kvm->slots_lock);
return pit;
fail_unregister:
kvm_io_bus_unregister_dev(kvm, KVM_PIO_BUS, &pit->dev);
-
fail:
+ mutex_unlock(&kvm->slots_lock);
kvm_unregister_irq_mask_notifier(kvm, 0, &pit->mask_notifier);
kvm_unregister_irq_ack_notifier(kvm, &pit_state->irq_ack_notifier);
kvm_free_irq_source_id(kvm, pit->irq_source_id);
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 52439fa8b463..8613422660b6 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -3867,7 +3867,7 @@ long kvm_arch_vm_ioctl(struct file *filp,
sizeof(struct kvm_pit_config)))
goto out;
create_pit:
- mutex_lock(&kvm->slots_lock);
+ mutex_lock(&kvm->lock);
r = -EEXIST;
if (kvm->arch.vpit)
goto create_pit_unlock;
@@ -3876,7 +3876,7 @@ long kvm_arch_vm_ioctl(struct file *filp,
if (kvm->arch.vpit)
r = 0;
create_pit_unlock:
- mutex_unlock(&kvm->slots_lock);
+ mutex_unlock(&kvm->lock);
break;
case KVM_GET_IRQCHIP: {
/* 0: PIC master, 1: PIC slave, 2: IOAPIC */