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Prevent shared-network races during simultaneous VM starts

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Serialize Windows shared-network lookup and creation so concurrently started VMs reuse the same network.
This commit is contained in:
James Stringer committed 2026-09-15 20:17:41 -04:00
1 parent 042559092b
commit d307a227d4
1 file changed
+20 -4
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src/backend_win/hcn_network.c
+20 -4
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@@ -27,6 +27,7 @@ typedef HRESULT (WINAPI *PFN_HcnOpenNetwork)(
/* ---- Loaded function pointers ---- */
static HMODULE g_hcn_dll = NULL;
static SRWLOCK g_network_lock = SRWLOCK_INIT;
static PFN_HcnCreateNetwork pfnCreateNet;
static PFN_HcnCreateEndpoint pfnCreateEp;
@@ -306,7 +307,9 @@ static void pick_nat_base_once(void)
const char *hcn_nat_subnet_base(void)
{
AcquireSRWLockExclusive(&g_network_lock);
pick_nat_base_once();
ReleaseSRWLockExclusive(&g_network_lock);
return g_nat_base;
}
@@ -322,10 +325,13 @@ HRESULT hcn_create_nat_network(GUID *network_id)
*network_id = APPSANDBOX_NAT_GUID;
AcquireSRWLockExclusive(&g_network_lock);
/* Reuse the existing AppSandbox NAT network if it's already up -
multiple VMs share one network, each with its own endpoint. */
if (hcn_network_exists(&APPSANDBOX_NAT_GUID))
if (hcn_network_exists(&APPSANDBOX_NAT_GUID)) {
ReleaseSRWLockExclusive(&g_network_lock);
return S_OK;
}
pick_nat_base_once();
@@ -353,6 +359,7 @@ HRESULT hcn_create_nat_network(GUID *network_id)
if (network && pfnCloseNet)
pfnCloseNet(network);
ReleaseSRWLockExclusive(&g_network_lock);
return hr;
}
@@ -368,8 +375,11 @@ HRESULT hcn_create_internal_network(GUID *network_id)
*network_id = APPSANDBOX_INTERNAL_GUID;
if (hcn_network_exists(&APPSANDBOX_INTERNAL_GUID))
AcquireSRWLockExclusive(&g_network_lock);
if (hcn_network_exists(&APPSANDBOX_INTERNAL_GUID)) {
ReleaseSRWLockExclusive(&g_network_lock);
return S_OK;
}
swprintf_s(settings, 1024,
L"{"
@@ -386,6 +396,7 @@ HRESULT hcn_create_internal_network(GUID *network_id)
}
if (network && pfnCloseNet) pfnCloseNet(network);
ReleaseSRWLockExclusive(&g_network_lock);
return hr;
}
@@ -402,8 +413,11 @@ HRESULT hcn_create_external_network(GUID *network_id, const wchar_t *adapter_nam
*network_id = APPSANDBOX_EXTERNAL_GUID;
if (hcn_network_exists(&APPSANDBOX_EXTERNAL_GUID))
AcquireSRWLockExclusive(&g_network_lock);
if (hcn_network_exists(&APPSANDBOX_EXTERNAL_GUID)) {
ReleaseSRWLockExclusive(&g_network_lock);
return S_OK;
}
/* Use specified adapter, or auto-detect */
if (adapter_name && adapter_name[0] != L'\0') {
@@ -412,6 +426,7 @@ HRESULT hcn_create_external_network(GUID *network_id, const wchar_t *adapter_nam
} else {
if (!get_default_adapter_name(adapter, 256)) {
ui_log(L"Error: No connected network adapter found for External network.");
ReleaseSRWLockExclusive(&g_network_lock);
return E_FAIL;
}
}
@@ -432,6 +447,7 @@ HRESULT hcn_create_external_network(GUID *network_id, const wchar_t *adapter_nam
}
if (network && pfnCloseNet) pfnCloseNet(network);
ReleaseSRWLockExclusive(&g_network_lock);
return hr;
}
@@ -486,7 +502,7 @@ HRESULT hcn_create_endpoint(const GUID *network_id, GUID *endpoint_id,
L"\"IpConfigurations\":[{\"IpAddress\":\"%S\",\"PrefixLength\":24}]"
L"%s}", net_guid_str, nat_ip, mac_settings);
} else if (IsEqualGUID(network_id, &APPSANDBOX_NAT_GUID)) {
pick_nat_base_once();
hcn_nat_subnet_base();
swprintf_s(settings, 1024,
L"{"
L"\"SchemaVersion\":{\"Major\":2,\"Minor\":0},"