server: Do not permit FileDispositionInformation to delete a file without write access.

dlls/ntdll/tests/file.c

@@ -1507,6 +1507,20 @@ static void test_file_disposition_information(void)
 
     /* cannot set disposition on readonly file */
     GetTempFileNameA( tmp_path, "dis", 0, buffer );
+    DeleteFileA( buffer );
+    handle = CreateFileA(buffer, GENERIC_WRITE | DELETE, 0, NULL, CREATE_ALWAYS, FILE_ATTRIBUTE_READONLY, 0);
+    ok( handle != INVALID_HANDLE_VALUE, "failed to create temp file\n" );
+    fdi.DoDeleteFile = TRUE;
+    res = pNtSetInformationFile( handle, &io, &fdi, sizeof fdi, FileDispositionInformation );
+    ok( res == STATUS_CANNOT_DELETE, "unexpected FileDispositionInformation result (expected STATUS_CANNOT_DELETE, got %x)\n", res );
+    CloseHandle( handle );
+    fileDeleted = GetFileAttributesA( buffer ) == INVALID_FILE_ATTRIBUTES && GetLastError() == ERROR_FILE_NOT_FOUND;
+    ok( !fileDeleted, "File shouldn't have been deleted\n" );
+    SetFileAttributesA( buffer, FILE_ATTRIBUTE_NORMAL );
+    DeleteFileA( buffer );
+
+    /* cannot set disposition on readonly file */
+    GetTempFileNameA( tmp_path, "dis", 0, buffer );
     handle = CreateFileA(buffer, GENERIC_WRITE | DELETE, 0, NULL, CREATE_ALWAYS, FILE_ATTRIBUTE_READONLY, 0);
     ok( handle != INVALID_HANDLE_VALUE, "failed to create temp file\n" );
     fdi.DoDeleteFile = TRUE;

server/fd.c

@@ -2244,6 +2244,13 @@ static void set_fd_disposition( struct fd *fd, int unlink )
         return;
     }
 
+    /* can't unlink files we don't have permission to access */
+    if (unlink && !(st.st_mode & (S_IWUSR | S_IWGRP | S_IWOTH)))
+    {
+        set_error( STATUS_CANNOT_DELETE );
+        return;
+    }
+
     fd->closed->unlink = unlink || (fd->options & FILE_DELETE_ON_CLOSE);
 }