06-25-2012
Quote:
Interposition is acheived by writing a shared library module (call it mylibrary.so as an example), compling it, then creating a special environment variable, LD_PRELOAD=mylibrary.so, and then running your code.
--> i have done all what you say , i have modified the code like that:
Quote:
size_t write(int fd, const void *buf, size_t count)
{
static size_t (*write_func)(int, const void *, size_t) = NULL;
/* get reference to original (libc provided) write */
if (!write_func)
{
write_func = (size_t(*)(int, const void *, size_t)) dlsym(RTLD_NEXT, "write");
}
return write_func(fd, buffer, sizeof (buffer));
}
I have a question please :how canget the buffer "const void *buf" because I want to change it before sending ?
Thank you so much for help
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SSP(3) BSD Library Functions Manual SSP(3)
NAME
ssp -- bounds checked libc functions
LIBRARY
Buffer Overflow Protection Library (libssp, -lssp)
SYNOPSIS
#include <ssp/stdio.h>
int
sprintf(char *str, const char *fmt, ...);
int
vsprintf(char *str, const char *fmt, va_list ap);
int
snprintf(char *str, size_t len, const char *fmt, ...);
int
vsnprintf(char *str, size_t len, const char *fmt, va_list ap);
char *
gets(char *str);
char *
fgets(char *str, int len, FILE *fp);
#include <ssp/string.h>
void *
memcpy(void *str, const void *ptr, size_t len);
void *
memmove(void *str, const void *ptr, size_t len);
void *
memset(void *str, int val, size_t len);
char *
strcpy(char *str, const char *ptr, size_t len);
char *
strcat(char *str, const char *ptr, size_t len);
char *
strncpy(char *str, const char *ptr, size_t len);
char *
strncat(char *str, const char *ptr, size_t len);
#include <ssp/strings.h>
void *
bcopy(const void *ptr, void *str, size_t len);
void *
bzero(void *str, size_t len);
#include <ssp/unistd.h>
ssize_t
read(int fd, void *str, size_t len);
int
readlink(const char * restrict path, char * restrict str, size_t len);
int
getcwd(char *str, size_t len);
DESCRIPTION
When _FORTIFY_SOURCE bounds checking is enabled as described below, the above functions get overwritten to use the __builtin_object_size(3)
function to compute the size of str, if known at compile time, and perform bounds check on it in order to avoid data buffer or stack buffer
overflows. If an overflow is detected, the routines will call abort(3).
To enable these function overrides the following should be added to the gcc(1) command line: ``-I/usr/include/ssp'' to override the standard
include files and ``-D_FORTIFY_SOURCE=1'' or ``-D_FORTIFY_SOURCE=2''.
If _FORTIFY_SOURCE is set to 1 the code will compute the maximum possible buffer size for str, and if set to 2 it will compute the minimum
buffer size.
SEE ALSO
gcc(1), __builtin_object_size(3), stdio(3), string(3), security(7)
HISTORY
The ssp library appeared NetBSD 4.0.
BSD
March 21, 2011 BSD