Avoid null pointer write in FFI

If a function returning variable length output was called with a
null output buffer but a non-zero output buffer length, FFI layer
would call memset(nullptr, 0, buffer_len) and crash.

Caught by Coverity.

1 files changed, 4 insertions, 1 deletions

diff --git a/src/lib/ffi/ffi_util.h b/src/lib/ffi/ffi_util.h
index 684b25870..f72af0a63 100644
--- a/src/lib/ffi/ffi_util.h
+++ b/src/lib/ffi/ffi_util.h
@@ -128,7 +128,10 @@ inline int write_output(uint8_t out[], size_t* out_len, const uint8_t buf[], siz
       }
    else
       {
-      Botan::clear_mem(out, avail);
+      if(out != nullptr)
+         {
+         Botan::clear_mem(out, avail);
+         }
       return BOTAN_FFI_ERROR_INSUFFICIENT_BUFFER_SPACE;
       }
    }