NetBSD/bin/systrace/systrace.1

.\"	$NetBSD: systrace.1,v 1.19 2002/11/02 20:04:20 provos Exp $
.\"	$OpenBSD: systrace.1,v 1.27 2002/08/05 23:27:53 provos Exp $
.\"
.\" Copyright 2002 Niels Provos <provos@citi.umich.edu>
.\" All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\"    notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\"    notice, this list of conditions and the following disclaimer in the
.\"    documentation and/or other materials provided with the distribution.
.\" 3. All advertising materials mentioning features or use of this software
.\"    must display the following acknowledgement:
.\"      This product includes software developed by Niels Provos.
.\" 4. The name of the author may not be used to endorse or promote products
.\"    derived from this software without specific prior written permission.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
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.\" Manual page, using -mandoc macros
.\"
.Dd June 3, 2002
.Dt SYSTRACE 1
.Os
.Sh NAME
.Nm systrace
.Nd generates and enforces system call policies
.Sh SYNOPSIS
.Nm systrace
.Op Fl aAituU
.Op Fl d Ar policydir
.Op Fl g Ar gui
.Op Fl f Ar file
.Op Fl c Ar uid:gid
.Op Fl p Ar pid
.Ar command ...
.Sh DESCRIPTION
The
.Nm
utility monitors and controls an application's access to the system by
enforcing access policies for system calls.
The
.Nm
utility might be used to trace an untrusted application's access to
the system.
Alternatively, it might be used to protect the system
from software bugs (such as buffer overflows) by constraining a
daemon's access to the system.
.Pp
The access policy can be generated interactively or obtained from a
policy file.
Operations not covered by the policy raise an alarm and
allow an user to refine the currently configured policy.
.Pp
The options are as follows:
.Bl -tag -width Dfxfile
.It Fl a
Enables automatic enforcement of configured policies.
An operation not covered by policy is denied and logged via
.Xr syslog 3 .
.It Fl A
Automatically generate a policy that allows every operation the
application executes.
The created policy functions as a base that can be refined.
.It Fl u
Do not perform aliasing on system call names.
Aliasing is enabled by default to group similar system calls into a
single compound name.
For example, system calls that read from the file system like
.Fn lstat
and
.Fn access
are translated to
.Fn fsread .
.It Fl i
Inherits the policy - child processes inherit policy of the parent binary.
.It Fl t
Uses text mode to ask for interactive policy generation.
.It Fl U
Ignore user configured policies and use only global system policies.
.It Fl d Ar policydir
Specifies an alternative location for the user's directory from
which policies are loaded and to which changed policies are stored.
.It Fl g Ar gui
Specifies an alternative location for the notification user interface.
.It Fl c Ar uid:gid
Specifies the
.Va uid
and
.Va gid
that the monitored application should be executed with.
This is useful in conjunction with privilege elevation and requires
root privileges.
.It Fl f Ar file
The policies specified in
.Ar file
are added to the policies that
.Nm
knows about.
.It Fl p Ar pid
Specifies the pid of a process that
.Nm
should attach to.
The full path name of the corresponding binary has to be specified
as
.Ar command .
.El
.Ss POLICY
The policy is specified via the following grammar:
.Bd -literal -offset 4
filter = expression "then" action errorcode logcode
expression = symbol | "not" expression | "(" expression ")" |
    expression "and" expression | expression "or" expression
symbol = string typeoff "match" cmdstring |
    string typeoff "eq" cmdstring | string typeoff "neq" cmdstring |
    string typeoff "sub" cmdstring | string typeoff "nsub" cmdstring |
    string typeoff "inpath" cmdstring | string typeoff "re" cmdstring |
    "true"
typeoff = /* empty */ | "[" number "]"
action = "permit" | "deny"
errorcode = /* empty */ | "[" string "]"
logcode = /* empty */ | "log"
.Ed
.Pp
The
.Va cmdstring
is an arbitrary string enclosed with quotation marks.
The
.Va errorcode
is used to return an
.Xr errno 2
value to the system call when using a
.Va deny
action.
The values
.Do
inherit
.Dc
and
.Do
detach
.Dc
have special meanings when used with a
.Va permit
rule for the
.Va execve
system call.
When using
.Do
inherit,
.Dc
the current policy is inherited for the new binary.
With
.Do
detach,
.Dc
.Nm
detaches from a process after successfully
completing
the
.Va execve
system call.
.Pp
The filter operations have the following meaning:
.Bl -hang -width Dinpath -offset AAA
.It match
Evaluates to true if file name globbing according to
.Xr fnmatch 3
succeeds.
.It eq
Evaluates to true if the system call argument matches
.Va cmdstring
exactly.
.It neq
This is the logical negation of
.Va eq .
.It sub
Performs a substring match on the system call argument.
.It nsub
This is the logical negation of
.Va sub .
.It inpath
Evaluates to true if the system call argument is a subpath of
.Va cmdstring .
.It re
Evaluates to true if the system call arguments matches
the specified regular expression.
.El
.Pp
By appending the
.Va log
statement to a rule, a matching system call and its arguments
is logged to
.Xr syslog 3 .
This is useful, for example, to log all invocations of the
.Va execve
system call.
.Pp
Policy entries may contain an appended predicate.
Predicates have the following format:
.Bd -literal -offset 4
", if" {"user", "group"} {"=", "!="} string
.Ed
.Pp
A rule is added to the configured policy only if its predicate
evaluates to true.
.Sh PRIVILEGE ELEVATION
With
.Nm
it is possible to remove setuid or setgid binaries, and use the
privilege elevation feature instead.
Single system calls can be executed with higher privileges if
specified by the policy.
For example,
.Bd -literal -offset 4
native-bind: sockaddr eq "inet-[0.0.0.0]:22" then permit as root
.Ed
.Pp
allows an unprivileged application to bind to a reserved port.
Privilege elevation requires that the
.Nm
process is executed as root.
.Pp
The following statements can be appended after the
.Va permit
in a policy to elevate the privileges for the matching system call:
.Bd -literal -offset 4
as user
as user:group
as :group
.Ed
.Pp
The effective
.Va uid
and
.Va gid
are elevated only for the duration of the system call, and are restored
to the old values afterwards.
The only exceptions are the
.Va seteuid
or
.Va setegid
system calls.
.Sh FILES
.Bl -tag -width xHOME/xsystrace -compact
.It Pa /dev/systrace
systrace device
.It Pa /etc/systrace
global systrace policies
.It Pa $HOME/.systrace
user specified policies
.El
.Sh EXAMPLES
An excerpt from a sample
.Xr ls 1
policy might look as follows:
.Bd -literal -offset 4
Policy: /bin/ls, Emulation: native
[...]
   native-fsread: filename eq "$HOME" then permit
   native-fchdir: permit
[...]
   native-fsread: filename eq "/tmp" then permit
   native-stat: permit
   native-fsread: filename match "$HOME/*" then permit
   native-fsread: filename eq "/etc/pwd.db" then permit
[...]
   native-fsread: filename eq "/etc" then deny[eperm], if group != wheel
.Ed
.Sh SEE ALSO
.Xr systrace 4
.Sh HISTORY
The
.Nm
utility first appeared in
.Ox 3.2 ,
and then in
.\" NEXTRELEASE
.Nx 2.0 .
.Sh AUTHORS
The
.Nm
utility was developed by Niels Provos.
.Sh BUGS
Applications that use clone()-like system calls to share the complete
address space between processes may be able to replace system call
arguments after they have been evaluated by
.Nm
and escape policy enforcement.