gh-114096: Restore privileges in _winapi.CreateJunction after creating the junction (GH-114089)

This avoids impact on later parts of the application which may be able to do things they otherwise shouldn't.

Author: zooba

Misc/NEWS.d/next/Windows/2024-01-15-23-53-25.gh-issue-114096.G-Myja.rst

@@ -0,0 +1,3 @@
+Process privileges that are activated for creating directory junctions are
+now restored afterwards, avoiding behaviour changes in other parts of the
+program.

Modules/_winapi.c

@@ -542,7 +542,12 @@ _winapi_CreateJunction_impl(PyObject *module, LPCWSTR src_path,
 {
     /* Privilege adjustment */
     HANDLE token = NULL;
-    TOKEN_PRIVILEGES tp;
+    struct {
+        TOKEN_PRIVILEGES base;
+        /* overallocate by a few array elements */
+        LUID_AND_ATTRIBUTES privs[4];
+    } tp, previousTp;
+    int previousTpSize = 0;
 
     /* Reparse data buffer */
     const USHORT prefix_len = 4;
@@ -566,17 +571,21 @@ _winapi_CreateJunction_impl(PyObject *module, LPCWSTR src_path,
 
     /* Adjust privileges to allow rewriting directory entry as a
        junction point. */
-    if (!OpenProcessToken(GetCurrentProcess(), TOKEN_ADJUST_PRIVILEGES, &token))
+    if (!OpenProcessToken(GetCurrentProcess(),
+                          TOKEN_ADJUST_PRIVILEGES | TOKEN_QUERY, &token)) {
         goto cleanup;
+    }
 
-    if (!LookupPrivilegeValue(NULL, SE_RESTORE_NAME, &tp.Privileges[0].Luid))
+    if (!LookupPrivilegeValue(NULL, SE_RESTORE_NAME, &tp.base.Privileges[0].Luid)) {
         goto cleanup;
+    }
 
-    tp.PrivilegeCount = 1;
-    tp.Privileges[0].Attributes = SE_PRIVILEGE_ENABLED;
-    if (!AdjustTokenPrivileges(token, FALSE, &tp, sizeof(TOKEN_PRIVILEGES),
-                               NULL, NULL))
+    tp.base.PrivilegeCount = 1;
+    tp.base.Privileges[0].Attributes = SE_PRIVILEGE_ENABLED;
+    if (!AdjustTokenPrivileges(token, FALSE, &tp.base, sizeof(previousTp),
+                               &previousTp.base, &previousTpSize)) {
         goto cleanup;
+    }
 
     if (GetFileAttributesW(src_path) == INVALID_FILE_ATTRIBUTES)
         goto cleanup;
@@ -657,8 +666,15 @@ _winapi_CreateJunction_impl(PyObject *module, LPCWSTR src_path,
 cleanup:
     ret = GetLastError();
 
-    CloseHandle(token);
-    CloseHandle(junction);
+    if (previousTpSize) {
+        AdjustTokenPrivileges(token, FALSE, &previousTp.base, previousTpSize,
+                              NULL, NULL);
+    }
+
+    if (token != NULL)
+        CloseHandle(token);
+    if (junction != NULL)
+        CloseHandle(junction);
     PyMem_RawFree(rdb);
 
     if (ret != 0)