UsespaceEmulator: Fix minor bugs in recvfrom() interception

* Pass the correct source address for copying tine addr_length.
  Previously, this was broken when addr_length was non-nullptr.

* Copy min(sizeof(address), address_length) bytes into address,
  instead of sizeof(address), which might be larger than the
  user buffer.

* Use sockaddr_storage instead of sockaddr_un. In practice they're
  both the same size, but this is what sockaddr_storage is for.

With this (in particular, the first fix), `ue /bin/ntpquery`
actually gets past the recvfrom() call :^)

1 files changed, 7 insertions, 4 deletions

diff --git a/DevTools/UserspaceEmulator/Emulator.cpp b/DevTools/UserspaceEmulator/Emulator.cpp
index db6c46689a..657a8fa390 100644
--- a/DevTools/UserspaceEmulator/Emulator.cpp
+++ b/DevTools/UserspaceEmulator/Emulator.cpp
@@ -599,13 +599,16 @@ int Emulator::virt$recvfrom(FlatPtr params_addr)
     mmu().copy_from_vm(&params, params_addr, sizeof(params));
     auto buffer = ByteBuffer::create_uninitialized(params.buffer.size);
 
-    sockaddr_un address;
-    if (params.addr)
-        mmu().copy_from_vm(&address, (FlatPtr)params.addr, sizeof(address));
+    if (!params.addr_length && params.addr)
+        return -EINVAL;
 
     socklen_t address_length = 0;
     if (params.addr_length)
-        mmu().copy_from_vm(&address_length, (FlatPtr)address_length, sizeof(address_length));
+        mmu().copy_from_vm(&address_length, (FlatPtr)params.addr_length, sizeof(address_length));
+
+    sockaddr_storage address;
+    if (params.addr)
+        mmu().copy_from_vm(&address, (FlatPtr)params.addr, min(sizeof(address), (size_t)address_length));
 
     int rc = recvfrom(params.sockfd, buffer.data(), buffer.size(), params.flags, params.addr ? (struct sockaddr*)&address : nullptr, params.addr_length ? &address_length : nullptr);
     if (rc < 0)