path: root/lib/libc/sys/tame.2

.\" $OpenBSD: tame.2,v 1.19 2015/08/26 05:55:53 doug Exp $
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.\" Copyright (c) 2015 Nicholas Marriott <nicm@openbsd.org>
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.Dd $Mdocdate: August 26 2015 $
.Dt TAME 2
.Os
.Sh NAME
.Nm tame
.Nd restrict system operations
.Sh SYNOPSIS
.In sys/tame.h
.Ft int
.Fn tame "int flags" "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 flags
or
.Ar paths .
.Pp
Use of
.Fn tame
in an application will require at least some study and understanding
of the interfaces called.
Subsequent calls to
.Fn tame
can reduce the abilities further, but abilities can never be regained.
.Pp
A process which attempts a restricted operation is killed with
.Dv SIGKILL .
If
.Dv TAME_ABORT
is set, then a non-blockable
.Dv SIGABRT
is delivered instead, possibly resulting in a
.Xr core 5
file.
.Pp
A
.Fa flags
value of 0 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
All
.Dv TAME_*
options below (with the exception of
.Dv TAME_ABORT )
permit the following system calls:
.Bd -ragged -offset indent
.Xr clock_getres 2 ,
.Xr clock_gettime 2 ,
.Xr fchdir 2 ,
.Xr getdtablecount 2 ,
.Xr getegid 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 nanosleep 2 ,
.Xr sendsyslog 2 ,
.Xr setitimer 2 ,
.Xr sigaction 2 ,
.Xr sigprocmask 2 ,
.Xr sigreturn 2 ,
.Xr umask 2 ,
.Xr wait4 2 .
.Ed
.Pp
Some system calls, when allowed, have restrictions applied to them:
.Pp
.Bl -tag -width TAME_TMPPATH -offset indent -compact
.It Xr access 2
May check for existence of
.Pa /etc/localtime .
.It Xr adjtime 2
Read-only, for
.Xr ntpd 8 .
.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
Setuid/setgid bits do not work, nor can the user or group be changed
on a file.
.It Xr open 2
May open
.Pa /etc/localtime ,
any files below
.Pa /usr/share/zoneinfo
and files ending in
.Pa libc.cat
below the directory
.Pa /usr/share/nls/ .
.It Xr readlink 2
May operate on
.Pa /etc/malloc.conf .
.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.
.It Xr tame 2
Can only reduce permissions; can only set a list of
.Pa paths
once.
.El
.Pp
The
.Ar flags
are specified as a bitwise OR of the following values:
.Bl -tag -width TAME_TMPPATH -offset indent
.It Dv TAME_MALLOC
To allow use of the
.Xr malloc 3
family of functions, the following system calls are permitted:
.Pp
.Xr getentropy 2 ,
.Xr madvise 2 ,
.Xr minherit 2 ,
.Xr mmap 2 ,
.Xr mprotect 2 ,
.Xr mquery 2 ,
.Xr munmap 2 .
.It Dv TAME_RW
The following system calls are permitted to allow most types of IO
operations on previously allocated file descriptors, including
libevent or handwritten async IO loops:
.Pp
.Xr poll 2 ,
.Xr kevent 2 ,
.Xr kqueue 2 ,
.Xr select 2 ,
.Xr close 2 ,
.Xr dup 2 ,
.Xr dup2 2 ,
.Xr dup3 2 ,
.Xr closefrom 2 ,
.Xr shutdown 2 ,
.Xr read 2 ,
.Xr readv 2 ,
.Xr pread 2 ,
.Xr preadv 2 ,
.Xr write 2 ,
.Xr writev 2 ,
.Xr pwrite 2 ,
.Xr pwritev 2 ,
.Xr ftruncate 2 ,
.Xr lseek 2 ,
.Xr fcntl 2 ,
.Xr fsync 2 ,
.Xr pipe 2 ,
.Xr pipe2 2 ,
.Xr socketpair 2 ,
.Xr getdents 2 ,
.Xr sendto 2 ,
.Xr sendmsg 2 ,
.Xr recvmsg 2 ,
.Xr recvfrom 2 ,
.Xr fstat 2 .
.It Dv TAME_STDIO
This subset is simply the combination of
.Dv TAME_MALLOC
and
.Dv TAME_RW .
As a result, all the expected functionalities of libc
stdio work.
.It Dv TAME_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 .
.It Dv TAME_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 ,
.Xr fstat 2 .
.It Dv TAME_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 rmdir 2 ,
.Xr renameat 2 ,
.Xr link 2 ,
.Xr linkat 2 ,
.Xr symlink 2 ,
.Xr unlink 2 ,
.Xr unlinkat 2 ,
.Xr mkdir 2 ,
.Xr mkdirat 2 .
.It Dv TAME_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 Dv TAME_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 Dv TAME_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 Dv TAME_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 Dv TAME_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 Dv TAME_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 the
.Dv TAME_INET
flag.
.It Dv TAME_CMSG
Allows passing of file descriptors using the
.Xr sendmsg 2
and
.Xr recvmsg 2
functions.
.It Dv TAME_IOCTL
Allows a subset of
.Xr ioctl 2
operations:
.Pp
.Dv FIOCLEX ,
.Dv FIONCLEX ,
.Dv FIONREAD ,
.Dv FIONBIO ,
.Dv FIOGETOWN ,
.Dv TIOCGETA ,
.Dv TIOCGPGRP ,
.Dv TIOCGWINSZ ,
.Dv TIOCSTI .
.It Dv TAME_PROC
Allows the following process relationship operations:
.Pp
.Xr fork 2 ,
.Xr vfork 2 ,
.Xr kill 2 ,
.Xr setgroups 2 ,
.Xr setresgid 2 ,
.Xr setresuid 2 ,
.It Dv TAME_ABORT
Deliver an unblockable
.Dv SIGABRT
upon violation instead of
.Dv SIGKILL .
.El
.Pp
A whitelist of permitted paths may be provided in
.Ar paths .
All other paths will return
.Er ENOENT .
.Sh RETURN VALUES
.Rv -std
.Sh ERRORS
.Fn tame
will fail if:
.Bl -tag -width Er
.It Bq Er EFAULT
.Fa paths
points outside the process's allocated address space.
.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 tame
system call appeared in
.Ox 5.8 .