解释代码#include <stdio.h> #include <stdlib.h> #include <unistd.h> #include <string.h> #include <sys/socket.h> #include <netinet/ip.h> #define PORT 9090 /* Changing this size will change the layout of the stack. * We have added 2 dummy arrays: in main() and myprintf(). * Instructors can change this value each year, so students * won't be able to use the solutions from the past. * Suggested value: between 0 and 300 */ #ifndef DUMMY_SIZE #define DUMMY_SIZE 100 #endif char *secret = "A secret message\n"; unsigned int target = 0x11223344; void myprintf(char *msg) { uintptr_t framep; // Copy the ebp value into framep, and print it out asm("movl %%ebp, %0" : "=r"(framep)); printf("The ebp value inside myprintf() is: 0x%.8x\n", framep); /* Change the size of the dummy array to randomize the parameters for this lab. Need to use the array at least once */ char dummy[DUMMY_SIZE]; memset(dummy, 0, DUMMY_SIZE); // This line has a format-string vulnerability printf(msg); printf("The value of the 'target' variable (after): 0x%.8x\n", target); } /* This function provides some helpful information. It is meant to * simplify the lab tasks. In practice, attackers need to figure * out the information by themselves. */ void helper() { printf("The address of the secret: 0x%.8x\n", (unsigned) secret); printf("The address of the 'target' variable: 0x%.8x\n", (unsigned) &target); printf("The value of the 'target' variable (before): 0x%.8x\n", target); }