NAME
pledge
—
restrict system operations
SYNOPSIS
#include
<unistd.h>
int
pledge
(const
char *promises, const
char *paths[]);
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 promises or paths.
Use of
pledge
() in
an application will require at least some study and understanding of the
interfaces called. Subsequent calls to pledge
() can
reduce the abilities further, but abilities can never be regained.
A process which attempts a restricted operation is killed with an
uncatchable SIGABRT
, delivering a core file if
possible.
A promises value of "" restricts the process to the _exit(2) system call. This can be used for pure computation operating on memory shared with another process.
Passing NULL
to
promises or paths specifies to
not change the current value.
Some system calls, when allowed, have restrictions applied to them:
- access(2)
- May check for existence of /etc/localtime.
- adjtime(2)
- Read-only, for ntpd(8).
- ioctl(2)
- Only the
FIONREAD
,FIONBIO
,FIOCLEX
, andFIONCLEX
operations are allowed by default. Various ioctl requests are allowed against specific file descriptors based upon the requests audio, bpf, disklabel, drm, inet, pf, route, tape, tty, and vmm. - chmod(2)
- fchmod(2)
- fchmodat(2)
- chown(2)
- lchown(2)
- fchown(2)
- fchownat(2)
- mkfifo(2)
- mknod(2)
- Setuid/setgid/sticky bits are ignored. The user or group cannot be changed on a file.
- mmap(2)
- mprotect(2)
PROT_EXEC
isn't allowed.- open(2)
- May open /etc/localtime and any files below /usr/share/zoneinfo.
- readlink(2)
- May operate on /etc/malloc.conf.
- sysctl(3)
- A small set of read-only operations are allowed, sufficient to support: getdomainname(3), gethostname(3), getifaddrs(3), uname(3), system sensor readings.
- pledge(2)
- Can only reduce permissions; can only set a list of paths once.
The promises is specified as a string, with space separated keywords:
- 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:
clock_getres(2), clock_gettime(2), close(2), closefrom(2), dup(2), dup2(2), dup3(2), fchdir(2), fcntl(2), fstat(2), fsync(2), ftruncate(2), getdents(2), getdtablecount(2), getegid(2), getentropy(2), geteuid(2), getgid(2), getgroups(2), getitimer(2), getlogin(2), getpgid(2), getpgrp(2), getpid(2), getppid(2), getresgid(2), getresuid(2), getrlimit(2), getsid(2), getthrid(2), gettimeofday(2), getuid(2), getuid(2), issetugid(2), kevent(2), kqueue(2), lseek(2), madvise(2), minherit(2), mmap(2), mprotect(2), mquery(2), munmap(2), nanosleep(2), pipe(2), pipe2(2), poll(2), pread(2), preadv(2), pwrite(2), pwritev(2), read(2), readv(2), recvfrom(2), recvmsg(2), select(2), sendmsg(2), sendsyslog(2), sendto(2), setitimer(2), shutdown(2), sigaction(2), sigprocmask(2), sigreturn(2), socketpair(2), umask(2), wait4(2), write(2), writev(2).
Note that sendto(2) is only permitted if its destination socket address is
NULL
. As a result, all the expected functionalities of libc stdio work. - rpath
- A number of system calls are allowed if they only cause read-only effects
on the filesystem:
chdir(2), getcwd(3), openat(2), fstatat(2), faccessat(2), readlinkat(2), lstat(2), chmod(2), fchmod(2), fchmodat(2), chflags(2), chflagsat(2), chown(2), fchown(2), fchownat(2), fstat(2), getfsstat(2).
- wpath
- A number of system calls are allowed and may cause write-effects on the
filesystem:
getcwd(3), openat(2), fstatat(2), faccessat(2), readlinkat(2), lstat(2), chmod(2), fchmod(2), fchmodat(2), chflags(2), chflagsat(2), chown(2), fchown(2), fchownat(2), fstat(2).
- cpath
- A number of system calls and sub-modes are allowed, which may create new
files or directories in the filesystem:
rename(2), renameat(2), link(2), linkat(2), symlink(2), symlinkat(2), unlink(2), unlinkat(2), mkdir(2), mkdirat(2), rmdir(2).
- dpath
- A number of system calls are allowed to create special files:
- tmppath
- A number of system calls are allowed to do operations in the
/tmp directory, including create, read, or write:
lstat(2), chmod(2), chflags(2), chown(2), unlink(2), fstat(2).
- inet
- The following system calls are allowed to operate in the
AF_INET
andAF_INET6
domains:socket(2), listen(2), bind(2), connect(2), accept4(2), accept(2), getpeername(2), getsockname(2), setsockopt(2), getsockopt(2).
setsockopt(2) has been reduced in functionality substantially.
- mcast
- In combination with inet give back functionality to setsockopt(2) for operating on multicast sockets.
- fattr
- The following system calls are allowed to make explicit changes to fields
in struct stat relating to a file:
utimes(2), futimes(2), utimensat(2), futimens(2), chmod(2), fchmod(2), fchmodat(2), chflags(2), chflagsat(2), chown(2), fchownat(2), lchown(2), fchown(2), utimes(2).
- chown
- The chown(2) family is allowed to change the user or group on a file.
- flock
- File locking via fcntl(2), flock(2), lockf(3), and open(2) is allowed. No distinction is made between shared and exclusive locks. This promise is required for unlock as well as lock.
- unix
- The following system calls are allowed to operate in the
AF_UNIX
domain:socket(2), listen(2), bind(2), connect(2), accept4(2), accept(2), getpeername(2), getsockname(2), setsockopt(2), getsockopt(2).
- dns
- Subsequent to a successful open(2) of /etc/resolv.conf, a few system calls become able to allow DNS network transactions:
- getpw
- This allows read-only opening of files in /etc for the getpwnam(3), getgrnam(3), getgrouplist(3), and initgroups(3) family of functions. They may also need to operate in a yp(8) environment, so a successful open(2) of /var/run/ypbind.lock enables inet operations.
- sendfd
- Allows sending of file descriptors using sendmsg(2). File descriptors referring to directories may not be passed.
- recvfd
- Allows receiving of file descriptors using recvmsg(2). File descriptors referring to directories may not be passed.
- tape
- Allow
MTIOCGET
andMTIOCTOP
operations against tape drives. - tty
- In addition to allowing read-write operations on
/dev/tty, this opens up a variety of
ioctl(2) requests used by tty devices. The following
ioctl(2) requests are permitted:
TIOCSPGRP
,TIOCGETA
,TIOCGPGRP
,TIOCGWINSZ
,TIOCSWINSZ
,TIOCSBRK
,TIOCCDTR
,TIOCSETA
,TIOCSETAW
andTIOCSETAF
.If tty is accompanied with rpath, revoke(2) is permitted.
- proc
- Allows the following process relationship operations:
fork(2), vfork(2), kill(2), getpriority(2), setpriority(2), setrlimit(2), setpgid(2), setsid(2).
- exec
- Allows a process to call
execve(2). Coupled with the 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
pledge
(). - prot_exec
- Allows the use of
PROT_EXEC
with mmap(2) and mprotect(2). - settime
- Allows the setting of system time, via the settimeofday(2), adjtime(2), and adjfreq(2) system calls.
- ps
- Allows enough sysctl(3) interfaces to allow inspection of processes operating on the system using programs like ps(1).
- vminfo
- Allows enough sysctl(3) interfaces to allow inspection of the system's virtual memory by programs like top(1) and vmstat(8).
- id
- Allows the following system calls which can change the rights of a
process:
setuid(2), seteuid(2), setreuid(2), setresuid(2), setgid(2), setegid(2), setregid(2), setresgid(2), setgroups(2), setlogin(2), setrlimit(2), getpriority(2), setpriority(2).
- pf
- Allows a subset of
ioctl(2) operations on the
pf(4) device:
DIOCADDRULE
,DIOCGETSTATUS
,DIOCNATLOOK
,DIOCRADDTABLES
,DIOCRCLRADDRS
,DIOCRCLRTABLES
,DIOCRCLRTSTATS
,DIOCRGETTSTATS
,DIOCRSETADDRS
,DIOCXBEGIN
,DIOCXCOMMIT
. - audio
- Allows a subset of
ioctl(2) operations on
audio(4) devices:
AUDIO_GETPOS
,AUDIO_GETPAR
,AUDIO_SETPAR
,AUDIO_START
,AUDIO_STOP
.See sio_open(3) for more information on using the sndio API in combination with
pledge
(). - bpf
- Allow
BIOCGSTATS
operation for statistics collection from a bpf device.
A whitelist of permitted paths may be provided in
paths. All other paths will return
ENOENT
. At least one promise is required to be
pledged in order to activate a whitelist.
RETURN VALUES
Upon successful completion, the value 0 is returned; otherwise the value -1 is returned and the global variable errno is set to indicate the error.
ERRORS
pledge
() will fail if:
- [
EFAULT
] - paths or one of its elements, or promises points outside the process's allocated address space.
- [
EINVAL
] - request is malformed or contains invalid keywords.
- [
ENAMETOOLONG
] - An element of paths is too large, prepending
cwd to it would exceed
PATH_MAX
bytes, or promises is too long. - [
EPERM
] - This process is attempting to increase permissions.
- [
E2BIG
] - The 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 (
ARG_MAX
).
HISTORY
The pledge
() system call first appeared in
OpenBSD 5.9.
BUGS
The path whitelist feature is not available at this time.