Fix NULL dereference in gfn_to_hva_prot()

gfn_to_memslot() can return NULL or invalid slot. We need to check slot
validity before accessing it.

Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Gleb Natapov <gleb@redhat.com>

1 files changed, 4 insertions, 2 deletions

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 979bff485fb0..a9dd682cf5e3 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -1064,10 +1064,12 @@ EXPORT_SYMBOL_GPL(gfn_to_hva);
 unsigned long gfn_to_hva_prot(struct kvm *kvm, gfn_t gfn, bool *writable)
 {
         struct kvm_memory_slot *slot = gfn_to_memslot(kvm, gfn);
-        if (writable)
+        unsigned long hva = __gfn_to_hva_many(slot, gfn, NULL, false);
+
+        if (!kvm_is_error_hva(hva) && writable)
                 *writable = !memslot_is_readonly(slot);
 
-        return __gfn_to_hva_many(gfn_to_memslot(kvm, gfn), gfn, NULL, false);
+        return hva;
 }
 
 static int kvm_read_hva(void *data, void __user *hva, int len)