Dammit, check for the proper return value...
% cat mmap-test.c
#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <sys/mman.h>
int main(int argc, char* argv[])
{
size_t len = 10;
int prot = PROT_EXEC | PROT_READ | PROT_WRITE;
int flags = MAP_PRIVATE | MAP_ANONYMOUS;
void *p = mmap (NULL, len, prot, flags, -1, 0);
int err = errno;
if (p != (void*) -1) {
printf("p is good\n");
munmap(p, len);
}
else {
printf("p is bad (%d)\n", err);
}
return 0;
}
% clang -Wall mmap-test.c -o mmap-test.exe
% ./mmap-test.exe
p is bad (13)
That is the permission denied.
Next, avoid W+X:
% cat mmap-test.c
#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <sys/mman.h>
int main(int argc, char* argv[])
{
size_t len = 10;
int prot = /*PROT_EXEC |*/ PROT_READ | PROT_WRITE;
int flags = MAP_PRIVATE | MAP_ANONYMOUS;
void *p = mmap (NULL, len, prot, flags, -1, 0);
int err = errno;
if (p != (void*) -1) {
printf("p is good\n");
munmap(p, len);
}
else {
printf("p is bad (%d)\n", err);
}
return 0;
}
It looks like W^X is the culprit.
Jeff
