.\"	$OpenBSD: systrace.4,v 1.8 2003/07/09 13:26:20 jmc Exp $
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.Dd May 26, 2002
.Dt SYSTRACE 4
.Os
.Sh NAME
.Nm systrace
.Nd enforce and generate policies for system calls
.Sh SYNOPSIS
.Cd "pseudo-device systrace 1"
.Sh DESCRIPTION
.Nm
attaches to processes and enforces policies for system calls.
A pseudo-device,
.Pa /dev/systrace ,
allows userland processes to control the behavior of
.Nm
through an
.Xr ioctl 2
interface.
.Sh SYSTEM CALL POLICIES
.Nm
can assign the following policies to system calls:
.Bl -tag -width SYSTR_POLICY_XXXXXX
.It SYSTR_POLICY_ASK
Send a message of the type
.Dv SYSTR_MSG_ASK ,
and put the process to sleep until a
.Dv STRIOCANSWER
.Xr ioctl 2
is made.
.It SYSTR_POLICY_PERMIT
Immediately allow the system call.
.It SYSTR_POLICY_NEVER
Immediately return an error code.
.El
.Sh SYSTRACE MESSAGES
A
.Xr read 2
operation on the
.Nm
pseudo-device will block if there are no pending messages, or
return the following structure:
.Bd -literal
struct str_message {
	int msg_type;
#define SYSTR_MSG_ASK	1
#define SYSTR_MSG_RES	2
#define SYSTR_MSG_EMUL	3
#define SYSTR_MSG_CHILD	4
	pid_t msg_pid;
	short msg_policy;
	union {
		struct str_msg_emul msg_emul;
		struct str_msg_ask msg_ask;
		struct str_msg_child msg_child;
	} msg_data;
};

struct str_msg_emul {
	char emul[SYSTR_EMULEN];
};

struct str_msg_ask {
	int code;
	int argsize;
	register_t args[SYSTR_MAXARGS];
	register_t rval[2];
	int result;
};

struct str_msg_child {
	pid_t new_pid;
};
.Ed
.Sh IOCTL INTERFACE
.Nm
supports the following
.Xr ioctl 2
commands:
.Bl -tag -width "xxxxxx"
.It Dv SYSTR_CLONE Fa "int"
Return a
.Nm
file descriptor for
further
.Xr ioctl 2
operations.
.El
.Bl -tag -width STRIOCXXXXXXXX
.It Dv STRIOCATTACH Fa "pid_t"
Attach to a process, unless:
.Bl -enum -compact -width 2n
.It
It's the process that's doing the attaching.
.It
It's a system process.
.It
It's being traced already.
.It
You do not own the process and you're not root.
.It
It's
.Xr init 8 ,
and the
kernel was not compiled with
.Cd option INSECURE .
.El
.It Dv STRIOCDETACH Fa "pid_t"
Wake up a process if it is waiting for an answer, and detach from it.
.It Dv STRIOCANSWER Fa "struct systrace_answer"
Tell
.Nm
what to do with a system call that was assigned a policy of
.Dv SYSTR_POLICY_ASK .
.Bd -literal
struct systrace_answer {
	pid_t stra_pid;     /* PID of process being traced */
	int stra_policy;    /* Policy to assign */
	int stra_error;     /* Return value of denied syscall
	                       (will return EPERM if zero) */
	int stra_flags;
#define	SYSTR_FLAGS_RESULT 0x0001    /* Report syscall result */
};
.Ed
.It Dv STRIOCREPORT Fa "pid_t"
Report the current emulation a process is using inside the
.Va msg_emul
structure.
.It Dv STRIOCREPLACE Fa "struct systrace_replace"
Arrange for system call arguments to be replaced by arguments
supplied by the monitoring process.
.Bd -literal
struct systrace_replace {
	pid_t strr_pid;
	int strr_nrepl;		/* # of arguments to replace */
	caddr_t	strr_base;		/* Base user memory */
	size_t strr_len;		/* Length of memory */
	int strr_argind[SYSTR_MAXARGS];	/* Argument indexes */
	size_t strr_off[SYSTR_MAXARGS];	/* Argument offsets */
	size_t strr_offlen[SYSTR_MAXARGS]; /* Argument sizes */
};
.Ed
.It Dv STRIOCIO Fa "struct systrace_io"
Copy data in/out of the process being traced.
.Bd -literal
struct systrace_io {
	pid_t strio_pid;    /* PID of process being traced */
	int strio_ops;
#define	SYSTR_READ	1
#define	SYSTR_WRITE	2
	void *strio_offs;
	void *strio_addr;
	size_t strio_len;
};
.Ed
.It Dv STRIOCPOLICY Fa "struct systrace_policy"
Manipulate the set of policies.
.Bd -literal
struct systrace_policy {
	int strp_op;
#define	SYSTR_POLICY_NEW	1    /* Allocate a new policy */
#define	SYSTR_POLICY_ASSIGN	2    /* Assign policy to process */
#define	SYSTR_POLICY_MODIFY	3    /* Modify an entry */
	int strp_num;
	union {
		struct {
			short code;
#define SYSTR_POLICY_ASK	0
#define SYSTR_POLICY_PERMIT	1
#define SYSTR_POLICY_NEVER	2
			short policy;
		} assign;
		pid_t pid;
		int maxents;
	} strp_data;
#define strp_pid	strp_data.pid
#define strp_maxents	strp_data.maxents
#define strp_code	strp_data.assign.code
#define strp_policy	strp_data.assign.policy
};
.Ed
.Pp
The
.Dv SYSTR_POLICY_NEW
operation allocates a new policy with all entries initialized to
.Dv SYSTR_POLICY_ASK ,
and returns the new policy number into
.Va strp_num .
The
.Dv SYSTR_POLICY_ASSIGN
operation attaches the policy identified by
.Va strp_num
to
.Va strp_pid ,
with a maximum of
.Va strp_maxents
entries.
The
.Dv SYSTR_POLICY_MODIFY
operation changes the entry indexed by
.Va strp_code
to
.Va strp_policy .
.It Dv STRIOCGETCWD Fa "pid_t"
Set the working directory of the current process to that of the
named process.
.It Dv STRIOCRESCWD
Restore the working directory of the current process.
.El
.Sh FILES
.Bl -tag -width "/dev/systrace" -compact
.It Pa /dev/systrace
system call tracing facility
.El
.Sh SEE ALSO
.Xr ioctl 2 ,
.Xr read 2 ,
.Xr options 4 ,
.Xr securelevel 7
.Sh HISTORY
The
.Nm
facility first appeared in
.Ox 3.2 .
.\" .Sh BUGS
.\" .Sh CAVEATS