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Top Forums Programming Reason for Segmentation fault Post 302142296 by andryk on Thursday 25th of October 2007 09:47:58 AM
Old 10-25-2007
Quote:
Originally Posted by royalibrahim
The following program fails with "Segmentation fault" error message, while I try to run in Ubuntu (Debian) Linux m/c. It is not creating any core file, so I could not cross examine it with the debugger. See the comments for much better understanding. Could any one tell me the exact reason why the program is failing?

Code:
int main( ) {
    char *ch; (or) ch = 'A';   // but if it assigned to any string then no segmentation fault
    int *p = (int*) &ch[0];   // or &ch[1], &ch[2], .... ch;      but &ch runs fine
    printf("%c", *p);           // Segmentation Fault: only if you use this print statement 
}

Well, i would say you're attempting to print a char from some odd pointer value (ptr on ptr on stack, huh ?) you got from an uninitialized var which is char *ch and ... thus accessing outside your 'legal' space therefore the core.
You attending some security course on coding and braging about it or just goofing around Smilie lol me just joking
 

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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
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