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#!/usr/bin/env python
#
# mountsnoop Trace mount() and umount syscalls.
# For Linux, uses BCC, eBPF. Embedded C.
#
# USAGE: mountsnoop [-h]
#
# Copyright (c) 2016 Facebook, Inc.
# Licensed under the Apache License, Version 2.0 (the "License")
#
# 14-Oct-2016 Omar Sandoval Created this.
from __future__ import print_function
import argparse
import bcc
import ctypes
import errno
import functools
import sys
bpf_text = r"""
#include <uapi/linux/ptrace.h>
#include <linux/sched.h>
#include <linux/nsproxy.h>
#include <linux/ns_common.h>
/*
* XXX: struct mnt_namespace is defined in fs/mount.h, which is private to the
* VFS and not installed in any kernel-devel packages. So, let's duplicate the
* important part of the definition. There are actually more members in the
* real struct, but we don't need them, and they're more likely to change.
*/
struct mnt_namespace {
atomic_t count;
struct ns_common ns;
};
/*
* XXX: this could really use first-class string support in BPF. target is a
* NUL-terminated path up to PATH_MAX in length. source and type are
* NUL-terminated strings up to PAGE_SIZE in length. data is a weird case: it's
* almost always a NUL-terminated string, but for some filesystems (e.g., older
* NFS variants), it's a binary structure with plenty of NUL bytes, so the
* kernel always copies up to PAGE_SIZE bytes, stopping when it hits a fault.
*
* The best we can do with the existing BPF helpers is to copy as much of each
* argument as we can. Our stack space is limited, and we need to leave some
* headroom for the rest of the function, so this should be a decent value.
*/
#define MAX_STR_LEN 412
enum event_type {
EVENT_MOUNT,
EVENT_MOUNT_SOURCE,
EVENT_MOUNT_TARGET,
EVENT_MOUNT_TYPE,
EVENT_MOUNT_DATA,
EVENT_MOUNT_RET,
EVENT_UMOUNT,
EVENT_UMOUNT_TARGET,
EVENT_UMOUNT_RET,
};
struct data_t {
enum event_type type;
pid_t pid, tgid;
union {
/* EVENT_MOUNT, EVENT_UMOUNT */
struct {
/* current->nsproxy->mnt_ns->ns.inum */
unsigned int mnt_ns;
char comm[TASK_COMM_LEN];
unsigned long flags;
} enter;
/*
* EVENT_MOUNT_SOURCE, EVENT_MOUNT_TARGET, EVENT_MOUNT_TYPE,
* EVENT_MOUNT_DATA, EVENT_UMOUNT_TARGET
*/
char str[MAX_STR_LEN];
/* EVENT_MOUNT_RET, EVENT_UMOUNT_RET */
int retval;
};
};
BPF_PERF_OUTPUT(events);
int kprobe__sys_mount(struct pt_regs *ctx, char __user *source,
char __user *target, char __user *type,
unsigned long flags)
{
/* sys_mount takes too many arguments */
char __user *data = (char __user *)PT_REGS_PARM5(ctx);
struct data_t event = {};
struct task_struct *task;
struct nsproxy *nsproxy;
struct mnt_namespace *mnt_ns;
event.pid = bpf_get_current_pid_tgid() & 0xffffffff;
event.tgid = bpf_get_current_pid_tgid() >> 32;
event.type = EVENT_MOUNT;
bpf_get_current_comm(event.enter.comm, sizeof(event.enter.comm));
event.enter.flags = flags;
task = (struct task_struct *)bpf_get_current_task();
bpf_probe_read(&nsproxy, sizeof(nsproxy), &task->nsproxy);
bpf_probe_read(&mnt_ns, sizeof(mnt_ns), &nsproxy->mnt_ns);
bpf_probe_read(&event.enter.mnt_ns, sizeof(event.enter.mnt_ns),
&mnt_ns->ns.inum);
events.perf_submit(ctx, &event, sizeof(event));
event.type = EVENT_MOUNT_SOURCE;
memset(event.str, 0, sizeof(event.str));
bpf_probe_read(event.str, sizeof(event.str), source);
events.perf_submit(ctx, &event, sizeof(event));
event.type = EVENT_MOUNT_TARGET;
memset(event.str, 0, sizeof(event.str));
bpf_probe_read(event.str, sizeof(event.str), target);
events.perf_submit(ctx, &event, sizeof(event));
event.type = EVENT_MOUNT_TYPE;
memset(event.str, 0, sizeof(event.str));
bpf_probe_read(event.str, sizeof(event.str), type);
events.perf_submit(ctx, &event, sizeof(event));
event.type = EVENT_MOUNT_DATA;
memset(event.str, 0, sizeof(event.str));
bpf_probe_read(event.str, sizeof(event.str), data);
events.perf_submit(ctx, &event, sizeof(event));
return 0;
}
int kretprobe__sys_mount(struct pt_regs *ctx)
{
struct data_t event = {};
event.type = EVENT_MOUNT_RET;
event.pid = bpf_get_current_pid_tgid() & 0xffffffff;
event.tgid = bpf_get_current_pid_tgid() >> 32;
event.retval = PT_REGS_RC(ctx);
events.perf_submit(ctx, &event, sizeof(event));
return 0;
}
int kprobe__sys_umount(struct pt_regs *ctx, char __user *target, int flags)
{
struct data_t event = {};
struct task_struct *task;
struct nsproxy *nsproxy;
struct mnt_namespace *mnt_ns;
event.pid = bpf_get_current_pid_tgid() & 0xffffffff;
event.tgid = bpf_get_current_pid_tgid() >> 32;
event.type = EVENT_UMOUNT;
bpf_get_current_comm(event.enter.comm, sizeof(event.enter.comm));
event.enter.flags = flags;
task = (struct task_struct *)bpf_get_current_task();
bpf_probe_read(&nsproxy, sizeof(nsproxy), &task->nsproxy);
bpf_probe_read(&mnt_ns, sizeof(mnt_ns), &nsproxy->mnt_ns);
bpf_probe_read(&event.enter.mnt_ns, sizeof(event.enter.mnt_ns),
&mnt_ns->ns.inum);
events.perf_submit(ctx, &event, sizeof(event));
event.type = EVENT_UMOUNT_TARGET;
memset(event.str, 0, sizeof(event.str));
bpf_probe_read(event.str, sizeof(event.str), target);
events.perf_submit(ctx, &event, sizeof(event));
return 0;
}
int kretprobe__sys_umount(struct pt_regs *ctx)
{
struct data_t event = {};
event.type = EVENT_UMOUNT_RET;
event.pid = bpf_get_current_pid_tgid() & 0xffffffff;
event.tgid = bpf_get_current_pid_tgid() >> 32;
event.retval = PT_REGS_RC(ctx);
events.perf_submit(ctx, &event, sizeof(event));
return 0;
}
"""
# sys/mount.h
MS_MGC_VAL = 0xc0ed0000
MS_MGC_MSK = 0xffff0000
MOUNT_FLAGS = [
('MS_RDONLY', 1),
('MS_NOSUID', 2),
('MS_NODEV', 4),
('MS_NOEXEC', 8),
('MS_SYNCHRONOUS', 16),
('MS_REMOUNT', 32),
('MS_MANDLOCK', 64),
('MS_DIRSYNC', 128),
('MS_NOATIME', 1024),
('MS_NODIRATIME', 2048),
('MS_BIND', 4096),
('MS_MOVE', 8192),
('MS_REC', 16384),
('MS_SILENT', 32768),
('MS_POSIXACL', 1 << 16),
('MS_UNBINDABLE', 1 << 17),
('MS_PRIVATE', 1 << 18),
('MS_SLAVE', 1 << 19),
('MS_SHARED', 1 << 20),
('MS_RELATIME', 1 << 21),
('MS_KERNMOUNT', 1 << 22),
('MS_I_VERSION', 1 << 23),
('MS_STRICTATIME', 1 << 24),
('MS_LAZYTIME', 1 << 25),
('MS_ACTIVE', 1 << 30),
('MS_NOUSER', 1 << 31),
]
UMOUNT_FLAGS = [
('MNT_FORCE', 1),
('MNT_DETACH', 2),
('MNT_EXPIRE', 4),
('UMOUNT_NOFOLLOW', 8),
]
TASK_COMM_LEN = 16 # linux/sched.h
MAX_STR_LEN = 412
class EventType(object):
EVENT_MOUNT = 0
EVENT_MOUNT_SOURCE = 1
EVENT_MOUNT_TARGET = 2
EVENT_MOUNT_TYPE = 3
EVENT_MOUNT_DATA = 4
EVENT_MOUNT_RET = 5
EVENT_UMOUNT = 6
EVENT_UMOUNT_TARGET = 7
EVENT_UMOUNT_RET = 8
class EnterData(ctypes.Structure):
_fields_ = [
('mnt_ns', ctypes.c_uint),
('comm', ctypes.c_char * TASK_COMM_LEN),
('flags', ctypes.c_ulong),
]
class DataUnion(ctypes.Union):
_fields_ = [
('enter', EnterData),
('str', ctypes.c_char * MAX_STR_LEN),
('retval', ctypes.c_int),
]
class Event(ctypes.Structure):
_fields_ = [
('type', ctypes.c_uint),
('pid', ctypes.c_uint),
('tgid', ctypes.c_uint),
('union', DataUnion),
]
def _decode_flags(flags, flag_list):
str_flags = []
for flag, bit in flag_list:
if flags & bit:
str_flags.append(flag)
flags &= ~bit
if flags or not str_flags:
str_flags.append('0x{:x}'.format(flags))
return str_flags
def decode_flags(flags, flag_list):
return '|'.join(_decode_flags(flags, flag_list))
def decode_mount_flags(flags):
str_flags = []
if flags & MS_MGC_MSK == MS_MGC_VAL:
flags &= ~MS_MGC_MSK
str_flags.append('MS_MGC_VAL')
str_flags.extend(_decode_flags(flags, MOUNT_FLAGS))
return '|'.join(str_flags)
def decode_umount_flags(flags):
return decode_flags(flags, UMOUNT_FLAGS)
def decode_errno(retval):
try:
return '-' + errno.errorcode[-retval]
except KeyError:
return str(retval)
_escape_chars = {
ord('\a'): '\\a',
ord('\b'): '\\b',
ord('\t'): '\\t',
ord('\n'): '\\n',
ord('\v'): '\\v',
ord('\f'): '\\f',
ord('\r'): '\\r',
ord('"'): '\\"',
ord('\\'): '\\\\',
}
def escape_character(c):
try:
return _escape_chars[c]
except KeyError:
if 0x20 <= c <= 0x7e:
return chr(c)
else:
return '\\x{:02x}'.format(c)
if sys.version_info.major < 3:
def decode_mount_string(s):
return '"{}"'.format(''.join(escape_character(ord(c)) for c in s))
else:
def decode_mount_string(s):
return '"{}"'.format(''.join(escape_character(c) for c in s))
def print_event(mounts, umounts, cpu, data, size):
event = ctypes.cast(data, ctypes.POINTER(Event)).contents
try:
if event.type == EventType.EVENT_MOUNT:
mounts[event.pid] = {
'pid': event.pid,
'tgid': event.tgid,
'mnt_ns': event.union.enter.mnt_ns,
'comm': event.union.enter.comm,
'flags': event.union.enter.flags,
}
elif event.type == EventType.EVENT_MOUNT_SOURCE:
mounts[event.pid]['source'] = event.union.str
elif event.type == EventType.EVENT_MOUNT_TARGET:
mounts[event.pid]['target'] = event.union.str
elif event.type == EventType.EVENT_MOUNT_TYPE:
mounts[event.pid]['type'] = event.union.str
elif event.type == EventType.EVENT_MOUNT_DATA:
# XXX: data is not always a NUL-terminated string
mounts[event.pid]['data'] = event.union.str
elif event.type == EventType.EVENT_UMOUNT:
umounts[event.pid] = {
'pid': event.pid,
'tgid': event.tgid,
'mnt_ns': event.union.enter.mnt_ns,
'comm': event.union.enter.comm,
'flags': event.union.enter.flags,
}
elif event.type == EventType.EVENT_UMOUNT_TARGET:
umounts[event.pid]['target'] = event.union.str
elif (event.type == EventType.EVENT_MOUNT_RET or
event.type == EventType.EVENT_UMOUNT_RET):
if event.type == EventType.EVENT_MOUNT_RET:
syscall = mounts.pop(event.pid)
call = ('mount({source}, {target}, {type}, {flags}, {data}) ' +
'= {retval}').format(
source=decode_mount_string(syscall['source']),
target=decode_mount_string(syscall['target']),
type=decode_mount_string(syscall['type']),
flags=decode_mount_flags(syscall['flags']),
data=decode_mount_string(syscall['data']),
retval=decode_errno(event.union.retval))
else:
syscall = umounts.pop(event.pid)
call = 'umount({target}, {flags}) = {retval}'.format(
target=decode_mount_string(syscall['target']),
flags=decode_umount_flags(syscall['flags']),
retval=decode_errno(event.union.retval))
print('{:16} {:<7} {:<7} {:<11} {}'.format(
syscall['comm'].decode(), syscall['tgid'], syscall['pid'],
syscall['mnt_ns'], call))
except KeyError:
# This might happen if we lost an event.
pass
def main():
parser = argparse.ArgumentParser(
description='trace mount() and umount() syscalls'
)
args = parser.parse_args()
mounts = {}
umounts = {}
b = bcc.BPF(text=bpf_text)
b['events'].open_perf_buffer(
functools.partial(print_event, mounts, umounts))
print('{:16} {:<7} {:<7} {:<11} {}'.format(
'COMM', 'PID', 'TID', 'MNT_NS', 'CALL'))
while True:
b.kprobe_poll()
if __name__ == '__main__':
main()