.\" $OpenBSD: systrace.1,v 1.31 2002/12/09 19:43:53 ian Exp $ .\" .\" Copyright 2002 Niels Provos .\" 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 .\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES .\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. .\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, .\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT .\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, .\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY .\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT .\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF .\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. .\" .\" Manual page, using -mandoc macros .\" .Dd June 3, 2002 .Dt SYSTRACE 1 .Os .Sh NAME .Nm systrace .Nd generate and enforce 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. Its privilege elevation feature can be used to obviate the need to run large, untrusted programs as root when only one or two system calls require root privilege. .Pp The access policy can be generated interactively or obtained from a policy file. Interactive policy generation will be performed by the ``notification user agent'', normally .Xr xsystrace 1 , unless text mode is specified via .Fl t . .Pp When running in ``automatic enforcement'' mode, 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, which must be specified as nonnegative integers (not as names). This is useful in conjunction with privilege elevation and requires root privilege. .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 AAA 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 AAA ", if" {"user", "group"} {"=", "!="} string .Ed .Pp A rule is added to the configured policy only if its predicate evaluates to true. .Pp The environment variables $HOME, $USER and $CWD are substituted in rules. Comments, begun by an unquoted '#' character and continuing to the end of the line, are ignored. .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 (except for 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 $HOME/.systrace user specified policies, one per binary, with slashes in the full pathname replaced by the underscore character. .El .Sh EXAMPLES An excerpt from a sample .Xr ls 1 policy might look as follows: .Bd -literal -offset AAA Policy: /bin/ls, Emulation: native [...] native-fsread: filename eq "$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 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.