KVM: x86: avoid vmalloc(0) in the KVM_SET_CPUID
This causes an ugly dmesg splat. Beautified syzkaller testcase:
#include <unistd.h>
#include <sys/syscall.h>
#include <sys/ioctl.h>
#include <fcntl.h>
#include <linux/kvm.h>
long r[8];
int main()
{
struct kvm_irq_routing ir = { 0 };
r[2] = open("/dev/kvm", O_RDWR);
r[3] = ioctl(r[2], KVM_CREATE_VM, 0);
r[4] = ioctl(r[3], KVM_SET_GSI_ROUTING, &ir);
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>
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 37af230..02e98f3 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -2935,7 +2935,7 @@
case KVM_SET_GSI_ROUTING: {
struct kvm_irq_routing routing;
struct kvm_irq_routing __user *urouting;
- struct kvm_irq_routing_entry *entries;
+ struct kvm_irq_routing_entry *entries = NULL;
r = -EFAULT;
if (copy_from_user(&routing, argp, sizeof(routing)))
@@ -2945,15 +2945,17 @@
goto out;
if (routing.flags)
goto out;
- r = -ENOMEM;
- entries = vmalloc(routing.nr * sizeof(*entries));
- if (!entries)
- goto out;
- r = -EFAULT;
- urouting = argp;
- if (copy_from_user(entries, urouting->entries,
- routing.nr * sizeof(*entries)))
- goto out_free_irq_routing;
+ if (routing.nr) {
+ r = -ENOMEM;
+ entries = vmalloc(routing.nr * sizeof(*entries));
+ if (!entries)
+ goto out;
+ r = -EFAULT;
+ urouting = argp;
+ if (copy_from_user(entries, urouting->entries,
+ routing.nr * sizeof(*entries)))
+ goto out_free_irq_routing;
+ }
r = kvm_set_irq_routing(kvm, entries, routing.nr,
routing.flags);
out_free_irq_routing: