/*
 * t_mmap_madvise_1.c
 *
 * Check that an mprotect(PROT_NONE) region cannot be read even after an
 * madvise(MADV_WILLNEED) has been executed on the region.
 *
 * Returns 0 if mprotect() protected the segment, 1 if the segment was readable
 * despite PROT_NONE.
 *
 * $Id: t_mmap_madvise_1.c,v 1.1 2011/10/30 15:10:34 me Exp me $
 */

#include <sys/types.h>
#include <sys/wait.h>
#include <sys/mman.h>

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <fcntl.h>
#include <unistd.h>
#include <err.h>

int
main(int argc, char *argv[])
{
        int fd;
        char *mem;
        char *tmpfile;
        char teststring[] = "hello, world!\0";
        int rc;
        char c0;
        int status;
        
        /* Setup: create a test file, write a test pattern, map it */
        tmpfile = tmpnam(NULL);

        fd = open(tmpfile, O_RDWR | O_CREAT | O_TRUNC, 0777);
        if (fd == -1)
                err(1, "open/creat failure");

        unlink(tmpfile);
        write(fd, teststring, strlen(teststring));
        fsync(fd);

        mem = mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0);
        if (mem == MAP_FAILED)
                err(1, "mmap failure");
        
        /* At this point the segment should be readable and reflect the file */
        rc = strcmp(mem, teststring);
        if (rc != 0)
                err(1, "unexpected map region");
        
        rc = mprotect(mem, 4096, PROT_NONE);
        if (rc == -1)
                err(1, "mprotect error");
        
        /* At this point the segment should no longer be readable */
        
        /* POSIX hat: this call might want to fail w/ EINVAL; we are offering
         * advice for a region that is invalid, posix_madvise() is marked as
         * failing w/ EINVAL if "The value of advice is invalid." ; we need
         * a more precise definition of invalid. */
        rc = madvise(mem, 4096, MADV_WILLNEED);
        if (rc == -1)
                err(1, "madvise failed");
        
        /* Segment should still not be readable */
        
        rc = fork();
        if (rc == 0) {
                c0 = mem[0];
                if (c0 == 'h')
                        exit(0);
                exit(1);
        }
        wait(&status);
        rc = 0;
        
        /* The child was able to read the segment. Uhoh. */
        if (WIFEXITED(status)) {
                rc = -1;
        }
        /* Child died via a signal (SEGV) */
        if (WIFSIGNALED(status)) {
                rc = 0;
        }
        
        munmap(mem, 4096);
        close(fd);
        
        printf("%d \n", rc);
        return (rc);
}