test of /proc/xxx/mem

secret-holder.c

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

void main(int argc, char **argv)
{
	char *secret = strdup(argv[1]);
	printf("I have a secret! It is located at %p and is %zu bytes long!\n", secret, strlen(secret));
	while (1) {}
	free(secret);
}

secret-stealer.c

#define _GNU_SOURCE /* asprintf isn't in standard C before C23 */
#include <stdlib.h>
#include <stdio.h>
#include <errno.h>

int main(int argc, char **argv)
{
	int pid = atoi(argv[1]);
	size_t addr = (size_t)strtoll(argv[2], NULL, 0);
	size_t size = (size_t)strtoll(argv[3], NULL, 0);
	char *path;
	asprintf(&path, "/proc/%d/mem", pid);
	FILE *fp = fopen(path, "r");
	if (!fp) {
		perror("couldn't open file");
		return 1;
	}
	free(path);
	fseek(fp, (long)addr, SEEK_SET);
	char *secret = malloc(size);
	fread(secret, size, 1, fp);
	fclose(fp);
	printf("the secret is: %.*s\n", (int)size, secret);
}