[S390] KVM: Read buffer overflow

Check whether index is within bounds before testing the element.
Signed-off-by: NRoel Kluin <roel.kluin@gmail.com>
Signed-off-by: NMartin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/kvm/sigp.c

@@ -169,7 +169,7 @@ static int __sigp_set_prefix(struct kvm_vcpu *vcpu, u16 cpu_addr, u32 address,
 			     unsigned long *reg)
 {
 	struct kvm_s390_float_interrupt *fi = &vcpu->kvm->arch.float_int;
-	struct kvm_s390_local_interrupt *li;
+	struct kvm_s390_local_interrupt *li = NULL;
 	struct kvm_s390_interrupt_info *inti;
 	int rc;
 	u8 tmp;
@@ -189,9 +189,10 @@ static int __sigp_set_prefix(struct kvm_vcpu *vcpu, u16 cpu_addr, u32 address,
 		return 2; /* busy */
 
 	spin_lock(&fi->lock);
-	li = fi->local_int[cpu_addr];
+	if (cpu_addr < KVM_MAX_VCPUS)
+		li = fi->local_int[cpu_addr];
 
-	if ((cpu_addr >= KVM_MAX_VCPUS) || (li == NULL)) {
+	if (li == NULL) {
 		rc = 1; /* incorrect state */
 		*reg &= SIGP_STAT_INCORRECT_STATE;
 		kfree(inti);