getpeername always gives bad file descriptor

Question

I have the following code, that i am trying to use to get the address of the other end of the socket, but getpeername() always fails with bad file descriptor error. What am i doing wrong?

#include <arpa/inet.h>
#include<syscall.h>
#include<errno.h>
#include <netinet/in.h>
#include<string.h>
#include<sys/socket.h>
#include<stdio.h>
#include<sys/ptrace.h>
#include<sys/types.h>
#include<sys/wait.h>
#include<unistd.h>
#include<sys/user.h>
#include<sys/syscall.h>   /* For SYS_write etc */
#include<stdlib.h>

#define ORIG_RAX 15
#define SYSCALL_MAXARGS 6
#define RDI 14

int main()
{
    //**********declarations and memory allocations**********//
    ssize_t size;
    long sys_call_number, temp_long;
    int status, temp, i, j, k, flag;

    struct sockaddr_in ip_addr_struct;
    socklen_t ip_addr_structlen = sizeof(ip_addr_struct);
    struct user_regs_struct regs;

    struct sockaddr_in* connect_struct;

    char* filepath = malloc(1024);
    char* fdpath = malloc(1024);
    char* message = malloc(1024);
    char* connect_ip = malloc(1024); 
    char* ip_addr = malloc(1024);

    char* temp_char1,* temp_char2;

    pid_t proc;

    //**********getting pid and attaching to process**********//
    scanf("%d",&proc);

    ptrace(PTRACE_ATTACH,proc, NULL, NULL);

    //**********starting the trace process**********//

    //The system call number used in switch() case to determine particular system   calls// 
    while(1)
    {
            wait(&status);
            if(WIFEXITED(status))
            {
                printf("****Process exited****\n");
                break;
            }
                ptrace(PTRACE_GETREGS, proc, NULL, &regs);
                sys_call_number = regs.orig_rax;

        switch(sys_call_number)
        {
            case 44:
                printf("sendto\n");
                //***printing the register values containing system call parameters***//
                printf("%llu - %llu - %llu - %llu - %llu - %llu\n", regs.rdi, regs.rsi, regs.rdx, regs.r10, regs.r8, regs.r9);
                //***getting the peer address***//
                errno = 0;
                temp = getpeername(regs.rdi, (struct sockaddr *)&ip_addr_struct, &ip_addr_structlen);
                if(temp == -1)
                {
                    printf("error is getpeername-%d-%s\n",temp,strerror(errno));
                    return -1;
                }

                int port = ntohs(ip_addr_struct.sin_port);
                inet_ntop(AF_INET, &(ip_addr_struct.sin_addr), ip_addr, 1024);
                printf("%d-%s\n", port, ip_addr);
                port = 0;
                //***reading message being send***//
                temp_char2 = message;
                j = 0;
                while( j < (regs.rdx/8) )
                {
                    temp_long = ptrace(PTRACE_PEEKDATA, proc, regs.rsi + (j*8) , NULL);
                    memcpy(temp_char2, &temp_long, 8);
                    temp_char2 += 8;
                    ++j;
                }
                temp_long = ptrace(PTRACE_PEEKDATA, proc, regs.rsi + (j*8) , NULL);
                memcpy(temp_char2, &temp_long, regs.rdx - (j*8) );
                message[regs.rdx] = '\0';
                printf("Message-%s-\n\n", message);
            break;
        }
    }
}

Here is the output from one such system call

sendto
14 - 32064144 - 884 - 16384 - 0 - 0
--1-Bad file descriptor
0-0.0.0.0
Message-GET /?gfe_rd=cr&ei=2WYzVLCjFq7M8gfLlICoDg HTTP/1.1^M
User-Agent: NetSurf/2.9 (Linux; x86_64)^M
Host: www.google.co.in^M
Accept: */
Accept-Encoding: gzip^M
 Cookie:PREF=ID=yu3vtr7i452389b4o236v4t28o37v723tn8vt0783tnv0723p78 N823748923bt87t2387b473287b8273t48

Answer 1

socket descriptor is not shared between two processes. the captured socket descriptor is only effective in the traced process, and not effective in the tracer process. that's why getpeername complains bad descriptor.
from the manual of ptrace:
The ptrace() system call provides a means by which a parent process may observe and control the execution of another process, and examine and change its core image and registers. It is primarily used to implement breakpoint debugging and system call tracing.
there's no word says they share process space, thus, they can not share socket descriptors, memory address, etc..