@@ -89,6 +89,44 @@ int main() {
8989 fclose (fd );
9090 }
9191
92+ // Use mmap to read out.txt and modify the contents in memory,
93+ // but make sure it's not overwritten on munmap
94+ {
95+ const char * readonlytext = "readonly mmap\0" ;
96+ const char * text = "write mmap\0" ;
97+ const char * path = "/yolo/outreadonly.txt" ;
98+ size_t readonlytextsize = strlen (readonlytext );
99+ size_t textsize = strlen (text );
100+
101+ int fd = open (path , O_RDWR | O_CREAT , (mode_t )0600 );
102+ // write contents to the file ( we don't want this to be overwritten on munmap )
103+ assert (write (fd , readonlytext , readonlytextsize ) != -1 );
104+ close (fd );
105+
106+ fd = open (path , O_RDWR );
107+ char * map = (char * )mmap (0 , textsize , PROT_READ , MAP_SHARED , fd , 0 );
108+ assert (map != MAP_FAILED );
109+
110+ for (size_t i = 0 ; i < textsize ; i ++ ) {
111+ map [i ] = text [i ];
112+ }
113+
114+ assert (munmap (map , textsize ) != -1 );
115+ close (fd );
116+ }
117+
118+ {
119+ FILE * fd = fopen ("/yolo/outreadonly.txt" , "r" );
120+ if (fd == NULL ) {
121+ printf ("failed to open /yolo/outreadonly.txt\n" );
122+ return 1 ;
123+ }
124+ char buffer [14 ];
125+ fread (buffer , 1 , 15 , fd );
126+ printf ("/yolo/outreadonly.txt content=%s\n" , buffer );
127+ fclose (fd );
128+ }
129+
92130 // MAP_PRIVATE
93131 {
94132 const char * text = "written mmap" ;
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