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/*
* gcc link_failure.c -o link_failure.so -shared -ldl
* LD_PRELOAD=./link_failure.so FAILURE_PATH=/etc/shadow ./test /etc/shadow
*/
#define _GNU_SOURCE
#include <dlfcn.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <stdarg.h>
#include <fcntl.h>
#include <string.h>
#include <errno.h>
#include <assert.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
typedef int (*link_type) (const char *oldpath, const char *newpath);
static link_type next_link;
static const char *failure_path = NULL;
int link (const char *oldpath, const char *newpath)
{
if (NULL == next_link)
{
next_link = dlsym (RTLD_NEXT, "link");
assert (NULL != next_link);
}
if (NULL == failure_path) {
failure_path = getenv ("FAILURE_PATH");
if (NULL == failure_path) {
fputs ("No FAILURE_PATH defined\n", stderr);
}
}
if ( (NULL != newpath)
&& (NULL != failure_path)
&& (strcmp (newpath, failure_path) == 0))
{
fprintf (stderr, "link FAILURE %s %s\n", oldpath, newpath);
errno = EIO;
return -1;
}
return next_link (oldpath, newpath);
}
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