.\" $OpenBSD: pledge.2,v 1.41 2017/03/28 16:07:07 bluhm Exp $
.\"
.\" Copyright (c) 2015 Nicholas Marriott <nicm@openbsd.org>
.\"
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.\" purpose with or without fee is hereby granted, provided that the above
.\" copyright notice and this permission notice appear in all copies.
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.Dd $Mdocdate: March 28 2017 $
.Dt PLEDGE 2
.Os
.Sh NAME
.Nm pledge
.Nd restrict system operations
.Sh SYNOPSIS
.In unistd.h
.Ft int
.Fn pledge "const char *promises" "const char *paths[]"
.Sh DESCRIPTION
The current process is forced into a restricted-service operating mode.
A few subsets are available, roughly described as computation, memory
management, read-write operations on file descriptors, opening of files,
networking.
In general, these modes were selected by studying the operation
of many programs using libc and other such interfaces, and setting
.Ar promises
or
.Ar paths .
.Pp
Use of
.Fn pledge
in an application will require at least some study and understanding
of the interfaces called.
Subsequent calls to
.Fn pledge
can reduce the abilities further, but abilities can never be regained.
.Pp
A process which attempts a restricted operation is killed with an uncatchable
.Dv SIGABRT ,
delivering a core file if possible.
.Pp
A
.Fa promises
value of "" restricts the process to the
.Xr _exit 2
system call.
This can be used for pure computation operating on memory shared
with another process.
.Pp
Passing
.Dv NULL
to
.Fa promises
or
.Fa paths
specifies to not change the current value.
.Pp
Some system calls, when allowed, have restrictions applied to them:
.Pp
.Bl -tag -width "readlink(2)" -offset indent -compact
.It Xr access 2
May check for existence of
.Pa /etc/localtime .
.Pp
.It Xr adjtime 2
Read-only, for
.Xr ntpd 8 .
.Pp
.It Xr ioctl 2
Only the
.Dv FIONREAD ,
.Dv FIONBIO ,
.Dv FIOCLEX ,
and
.Dv FIONCLEX
operations are allowed by default.
Various ioctl requests are allowed against specific file descriptors
based upon the requests
.Va audio ,
.Va bpf ,
.Va disklabel ,
.Va drm ,
.Va inet ,
.Va pf ,
.Va route ,
.Va tape ,
.Va tty ,
and
.Va vmm .
.Pp
.It Xr chmod 2
.It Xr fchmod 2
.It Xr fchmodat 2
.It Xr chown 2
.It Xr lchown 2
.It Xr fchown 2
.It Xr fchownat 2
.It Xr mkfifo 2
.It Xr mknod 2
Setuid/setgid/sticky bits are ignored.
The user or group cannot be changed on a file.
.Pp
.It Xr mmap 2
.It Xr mprotect 2
.Dv PROT_EXEC
isn't allowed.
.Pp
.It Xr open 2
May open
.Pa /etc/localtime
and any files below
.Pa /usr/share/zoneinfo .
.Pp
.It Xr readlink 2
May operate on
.Pa /etc/malloc.conf .
.Pp
.It Xr sysctl 3
A small set of read-only operations are allowed, sufficient to
support:
.Xr getdomainname 3 ,
.Xr gethostname 3 ,
.Xr getifaddrs 3 ,
.Xr uname 3 ,
system sensor readings.
.Pp
.It Xr pledge 2
Can only reduce permissions; can only set a list of
.Pa paths
once.
.El
.Pp
The
.Ar promises
is specified as a string, with space separated keywords:
.Bl -tag -width "tmppath" -offset indent
.It Va stdio
The following system calls are permitted to allow most basic functions
in libc, including memory allocation, most types of IO operations on
previously allocated file descriptors:
.Pp
.Xr clock_getres 2 ,
.Xr clock_gettime 2 ,
.Xr close 2 ,
.Xr closefrom 2 ,
.Xr dup 2 ,
.Xr dup2 2 ,
.Xr dup3 2 ,
.Xr fchdir 2 ,
.Xr fcntl 2 ,
.Xr fstat 2 ,
.Xr fsync 2 ,
.Xr ftruncate 2 ,
.Xr getdents 2 ,
.Xr getdtablecount 2 ,
.Xr getegid 2 ,
.Xr getentropy 2 ,
.Xr geteuid 2 ,
.Xr getgid 2 ,
.Xr getgroups 2 ,
.Xr getitimer 2 ,
.Xr getlogin 2 ,
.Xr getpgid 2 ,
.Xr getpgrp 2 ,
.Xr getpid 2 ,
.Xr getppid 2 ,
.Xr getresgid 2 ,
.Xr getresuid 2 ,
.Xr getrlimit 2 ,
.Xr getsid 2 ,
.Xr getthrid 2 ,
.Xr gettimeofday 2 ,
.Xr getuid 2 ,
.Xr getuid 2 ,
.Xr issetugid 2 ,
.Xr kevent 2 ,
.Xr kqueue 2 ,
.Xr lseek 2 ,
.Xr madvise 2 ,
.Xr minherit 2 ,
.Xr mmap 2 ,
.Xr mprotect 2 ,
.Xr mquery 2 ,
.Xr munmap 2 ,
.Xr nanosleep 2 ,
.Xr pipe 2 ,
.Xr pipe2 2 ,
.Xr poll 2 ,
.Xr pread 2 ,
.Xr preadv 2 ,
.Xr pwrite 2 ,
.Xr pwritev 2 ,
.Xr read 2 ,
.Xr readv 2 ,
.Xr recvfrom 2 ,
.Xr recvmsg 2 ,
.Xr select 2 ,
.Xr sendmsg 2 ,
.Xr sendsyslog 2 ,
.Xr sendto 2 ,
.Xr setitimer 2 ,
.Xr shutdown 2 ,
.Xr sigaction 2 ,
.Xr sigprocmask 2 ,
.Xr sigreturn 2 ,
.Xr socketpair 2 ,
.Xr umask 2 ,
.Xr wait4 2 ,
.Xr write 2 ,
.Xr writev 2 .
.Pp
Note that
.Xr sendto 2
is only permitted if its destination socket address is
.Dv NULL .
As a result, all the expected functionalities of libc stdio work.
.It Va rpath
A number of system calls are allowed if they only cause
read-only effects on the filesystem:
.Pp
.Xr chdir 2 ,
.Xr getcwd 3 ,
.Xr openat 2 ,
.Xr fstatat 2 ,
.Xr faccessat 2 ,
.Xr readlinkat 2 ,
.Xr lstat 2 ,
.Xr chmod 2 ,
.Xr fchmod 2 ,
.Xr fchmodat 2 ,
.Xr chflags 2 ,
.Xr chflagsat 2 ,
.Xr chown 2 ,
.Xr fchown 2 ,
.Xr fchownat 2 ,
.Xr fstat 2 ,
.Xr getfsstat 2 .
.It Va wpath
A number of system calls are allowed and may cause
write-effects on the filesystem:
.Pp
.Xr getcwd 3 ,
.Xr openat 2 ,
.Xr fstatat 2 ,
.Xr faccessat 2 ,
.Xr readlinkat 2 ,
.Xr lstat 2 ,
.Xr chmod 2 ,
.Xr fchmod 2 ,
.Xr fchmodat 2 ,
.Xr chflags 2 ,
.Xr chflagsat 2 ,
.Xr chown 2 ,
.Xr fchown 2 ,
.Xr fchownat 2 ,
.Xr fstat 2 .
.It Va cpath
A number of system calls and sub-modes are allowed, which may
create new files or directories in the filesystem:
.Pp
.Xr rename 2 ,
.Xr renameat 2 ,
.Xr link 2 ,
.Xr linkat 2 ,
.Xr symlink 2 ,
.Xr symlinkat 2 ,
.Xr unlink 2 ,
.Xr unlinkat 2 ,
.Xr mkdir 2 ,
.Xr mkdirat 2 ,
.Xr rmdir 2 .
.It Va dpath
A number of system calls are allowed to create special files:
.Pp
.Xr mkfifo 2 ,
.Xr mknod 2 .
.It Va tmppath
A number of system calls are allowed to do operations in the
.Pa /tmp
directory, including create, read, or write:
.Pp
.Xr lstat 2 ,
.Xr chmod 2 ,
.Xr chflags 2 ,
.Xr chown 2 ,
.Xr unlink 2 ,
.Xr fstat 2 .
.It Va inet
The following system calls are allowed to operate in the
.Dv AF_INET
and
.Dv AF_INET6
domains:
.Pp
.Xr socket 2 ,
.Xr listen 2 ,
.Xr bind 2 ,
.Xr connect 2 ,
.Xr accept4 2 ,
.Xr accept 2 ,
.Xr getpeername 2 ,
.Xr getsockname 2 ,
.Xr setsockopt 2 ,
.Xr getsockopt 2 .
.Pp
.Xr setsockopt 2
has been reduced in functionality substantially.
.It Va mcast
In combination with
.Va inet
give back functionality to
.Xr setsockopt 2
for operating on multicast sockets.
.It Va fattr
The following system calls are allowed to make explicit changes
to fields in
.Va struct stat
relating to a file:
.Pp
.Xr utimes 2 ,
.Xr futimes 2 ,
.Xr utimensat 2 ,
.Xr futimens 2 ,
.Xr chmod 2 ,
.Xr fchmod 2 ,
.Xr fchmodat 2 ,
.Xr chflags 2 ,
.Xr chflagsat 2 ,
.Xr chown 2 ,
.Xr fchownat 2 ,
.Xr lchown 2 ,
.Xr fchown 2 ,
.Xr utimes 2 .
.It Va chown
The
.Xr chown 2
family is allowed to change the user or group on a file.
.It Va flock
File locking via
.Xr fcntl 2 ,
.Xr flock 2 ,
.Xr lockf 3 ,
and
.Xr open 2
is allowed.
No distinction is made between shared and exclusive locks.
This promise is required for unlock as well as lock.
.It Va unix
The following system calls are allowed to operate in the
.Dv AF_UNIX
domain:
.Pp
.Xr socket 2 ,
.Xr listen 2 ,
.Xr bind 2 ,
.Xr connect 2 ,
.Xr accept4 2 ,
.Xr accept 2 ,
.Xr getpeername 2 ,
.Xr getsockname 2 ,
.Xr setsockopt 2 ,
.Xr getsockopt 2 .
.It Va dns
Subsequent to a successful
.Xr open 2
of
.Pa /etc/resolv.conf ,
a few system calls become able to allow DNS network transactions:
.Pp
.Xr sendto 2 ,
.Xr recvfrom 2 ,
.Xr socket 2 ,
.Xr connect 2 .
.It Va getpw
This allows read-only opening of files in
.Pa /etc
for the
.Xr getpwnam 3 ,
.Xr getgrnam 3 ,
.Xr getgrouplist 3 ,
and
.Xr initgroups 3
family of functions.
They may also need to operate in a
.Xr yp 8
environment, so a successful
.Xr open 2
of
.Pa /var/run/ypbind.lock
enables
.Va inet
operations.
.It Va sendfd
Allows sending of file descriptors using
.Xr sendmsg 2 .
File descriptors referring to directories may not be passed.
.It Va recvfd
Allows receiving of file descriptors using
.Xr recvmsg 2 .
File descriptors referring to directories may not be passed.
.It Va tape
Allow
.Dv MTIOCGET
and
.Dv MTIOCTOP
operations against tape drives.
.It Va tty
In addition to allowing read-write operations on
.Pa /dev/tty ,
this opens up a variety of
.Xr ioctl 2
requests used by tty devices.
The following
.Xr ioctl 2
requests are permitted:
.Dv TIOCSPGRP ,
.Dv TIOCGETA ,
.Dv TIOCGPGRP ,
.Dv TIOCGWINSZ ,
.Dv TIOCSWINSZ ,
.Dv TIOCSBRK ,
.Dv TIOCCDTR ,
.Dv TIOCSETA ,
.Dv TIOCSETAW
and
.Dv TIOCSETAF .
.Pp
If
.Va tty
is accompanied with
.Va rpath ,
.Xr revoke 2
is permitted.
.It Va proc
Allows the following process relationship operations:
.Pp
.Xr fork 2 ,
.Xr vfork 2 ,
.Xr kill 2 ,
.Xr getpriority 2 ,
.Xr setpriority 2 ,
.Xr setrlimit 2 ,
.Xr setpgid 2 ,
.Xr setsid 2 .
.It Va exec
Allows a process to call
.Xr execve 2 .
Coupled with the
.Va proc
promise, this allows a process to fork and execute another program.
The new program starts running without pledge active and hopefully
makes a new
.Fn pledge .
.It Va prot_exec
Allows the use of
.Dv PROT_EXEC
with
.Xr mmap 2
and
.Xr mprotect 2 .
.It Va settime
Allows the setting of system time, via the
.Xr settimeofday 2 ,
.Xr adjtime 2 ,
and
.Xr adjfreq 2
system calls.
.It Va ps
Allows enough
.Xr sysctl 3
interfaces to allow inspection of processes operating on the system using
programs like
.Xr ps 1 .
.It Va vminfo
Allows enough
.Xr sysctl 3
interfaces to allow inspection of the system's virtual memory by
programs like
.Xr top 1
and
.Xr vmstat 8 .
.It Va id
Allows the following system calls which can change the rights of a
process:
.Pp
.Xr setuid 2 ,
.Xr seteuid 2 ,
.Xr setreuid 2 ,
.Xr setresuid 2 ,
.Xr setgid 2 ,
.Xr setegid 2 ,
.Xr setregid 2 ,
.Xr setresgid 2 ,
.Xr setgroups 2 ,
.Xr setlogin 2 ,
.Xr setrlimit 2 ,
.Xr getpriority 2 ,
.Xr setpriority 2 .
.It Va pf
Allows a subset of
.Xr ioctl 2
operations on the
.Xr pf 4
device:
.Pp
.Dv DIOCADDRULE ,
.Dv DIOCGETSTATUS ,
.Dv DIOCNATLOOK ,
.Dv DIOCRADDTABLES ,
.Dv DIOCRCLRADDRS ,
.Dv DIOCRCLRTABLES ,
.Dv DIOCRCLRTSTATS ,
.Dv DIOCRGETTSTATS ,
.Dv DIOCRSETADDRS ,
.Dv DIOCXBEGIN ,
.Dv DIOCXCOMMIT .
.It Va audio
Allows a subset of
.Xr ioctl 2
operations on
.Xr audio 4
devices:
.Pp
.Dv AUDIO_GETPOS ,
.Dv AUDIO_GETPAR ,
.Dv AUDIO_SETPAR ,
.Dv AUDIO_START ,
.Dv AUDIO_STOP .
.Pp
See
.Xr sio_open 3
for more information on using the sndio API in combination with
.Fn pledge .
.It Va bpf
Allow
.Dv BIOCGSTATS
operation for statistics collection from a bpf device.
.El
.Pp
A whitelist of permitted paths may be provided in
.Ar paths .
All other paths will return
.Er ENOENT .
At least one promise is required to be pledged in order to activate a whitelist.
.Sh RETURN VALUES
.Rv -std
.Sh ERRORS
.Fn pledge
will fail if:
.Bl -tag -width Er
.It Bq Er EFAULT
.Fa paths
or one of its elements, or
.Fa promises
points outside the process's allocated address space.
.It Bq Er EINVAL
.Ar request
is malformed or contains invalid keywords.
.It Bq Er ENAMETOOLONG
An element of
.Fa paths
is too large, prepending
.Fa cwd
to it would exceed
.Dv PATH_MAX
bytes, or
.Fa promises
is too long.
.It Bq Er EPERM
This process is attempting to increase permissions.
.It Bq Er E2BIG
The
.Ar paths
array is too large, or the total number of bytes exceeds a
system-imposed limit.
The limit in the system as released is 262144 bytes
.Pf ( Dv ARG_MAX ) .
.El
.Sh HISTORY
The
.Fn pledge
system call first appeared in
.Ox 5.9 .
.Sh BUGS
The path whitelist feature is not available at this time.