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// SPDX-License-Identifier: GPL-2.0
/*
* Copyright (c) 2018 Dmitry Safonov, Arista Networks
*
* MAP_POPULATE | MAP_PRIVATE should COW VMA pages.
*/
#define _GNU_SOURCE
#include <errno.h>
#include <fcntl.h>
#include <sys/mman.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#define MMAP_SZ 4096
#define BUG_ON(condition, description) \
do { \
if (condition) { \
fprintf(stderr, "[FAIL]\t%s:%d\t%s:%s\n", __func__, \
__LINE__, (description), strerror(errno)); \
exit(1); \
} \
} while (0)
static int parent_f(int sock, unsigned long *smap, int child)
{
int status, ret;
ret = read(sock, &status, sizeof(int));
BUG_ON(ret <= 0, "read(sock)");
*smap = 0x22222BAD;
ret = msync(smap, MMAP_SZ, MS_SYNC);
BUG_ON(ret, "msync()");
ret = write(sock, &status, sizeof(int));
BUG_ON(ret <= 0, "write(sock)");
waitpid(child, &status, 0);
BUG_ON(!WIFEXITED(status), "child in unexpected state");
return WEXITSTATUS(status);
}
static int child_f(int sock, unsigned long *smap, int fd)
{
int ret, buf = 0;
smap = mmap(0, MMAP_SZ, PROT_READ | PROT_WRITE,
MAP_PRIVATE | MAP_POPULATE, fd, 0);
BUG_ON(smap == MAP_FAILED, "mmap()");
BUG_ON(*smap != 0xdeadbabe, "MAP_PRIVATE | MAP_POPULATE changed file");
ret = write(sock, &buf, sizeof(int));
BUG_ON(ret <= 0, "write(sock)");
ret = read(sock, &buf, sizeof(int));
BUG_ON(ret <= 0, "read(sock)");
BUG_ON(*smap == 0x22222BAD, "MAP_POPULATE didn't COW private page");
BUG_ON(*smap != 0xdeadbabe, "mapping was corrupted");
return 0;
}
int main(int argc, char **argv)
{
int sock[2], child, ret;
FILE *ftmp;
unsigned long *smap;
ftmp = tmpfile();
BUG_ON(!ftmp, "tmpfile()");
ret = ftruncate(fileno(ftmp), MMAP_SZ);
BUG_ON(ret, "ftruncate()");
smap = mmap(0, MMAP_SZ, PROT_READ | PROT_WRITE,
MAP_SHARED, fileno(ftmp), 0);
BUG_ON(smap == MAP_FAILED, "mmap()");
*smap = 0xdeadbabe;
/* Probably unnecessary, but let it be. */
ret = msync(smap, MMAP_SZ, MS_SYNC);
BUG_ON(ret, "msync()");
ret = socketpair(PF_LOCAL, SOCK_SEQPACKET, 0, sock);
BUG_ON(ret, "socketpair()");
child = fork();
BUG_ON(child == -1, "fork()");
if (child) {
ret = close(sock[0]);
BUG_ON(ret, "close()");
return parent_f(sock[1], smap, child);
}
ret = close(sock[1]);
BUG_ON(ret, "close()");
return child_f(sock[0], smap, fileno(ftmp));
}
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