SYSTRACE(4)               OpenBSD Programmer's Manual              SYSTRACE(4)

NAME
     systrace - enforce and generate policies for system calls

SYNOPSIS
     pseudo-device systrace [count]

DESCRIPTION
     systrace attaches to processes and enforces policies for system calls.  A
     pseudo-device, /dev/systrace, allows userland processes to control the
     behavior of systrace through an ioctl(2) interface.

SYSTEM CALL POLICIES
     systrace can assign the following policies to system calls:

     SYSTR_POLICY_ASK     Send a message of the type SYSTR_MSG_ASK, and put
                          the process to sleep until a STRIOCANSWER ioctl(2)
                          is made.

     SYSTR_POLICY_PERMIT  Immediately allow the system call.

     SYSTR_POLICY_NEVER   Immediately return an error code.

SYSTRACE MESSAGES
     A read(2) operation on the systrace pseudo-device will block if there are
     no pending messages, or return the following structure:

     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;
     };

IOCTL INTERFACE
     systrace supports the following ioctl(2) commands:

     SYSTR_CLONE int
                     Return a systrace file descriptor for further ioctl(2)
                     operations.

     STRIOCATTACH pid_t
                     Attach to a process, unless:
                     1.  It's the process that's doing the attaching.
                     2.  It's a system process.
                     3.  It's being traced already.
                     4.  You do not own the process and you're not root.
                     5.  It's init(8), and the kernel was not compiled with
                         option INSECURE.

     STRIOCDETACH pid_t
                     Wake up a process if it is waiting for an answer, and de-
                     tach from it.

     STRIOCANSWER struct systrace_answer
                     Tell systrace what to do with a system call that was as-
                     signed a policy of SYSTR_POLICY_ASK.

                     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 */
                     };

     STRIOCREPORT pid_t
                     Report the current emulation a process is using inside
                     the msg_emul structure.

     STRIOCREPLACE struct systrace_replace
                     Arrange for system call arguments to be replaced by argu-
                     ments supplied by the monitoring process.

                     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 */
                     };

     STRIOCIO struct systrace_io
                     Copy data in/out of the process being traced.

                     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;
                     };

     STRIOCPOLICY struct systrace_policy
                     Manipulate the set of policies.

                     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
                     };

                     The SYSTR_POLICY_NEW operation allocates a new policy
                     with all entries initialized to SYSTR_POLICY_ASK, and re-
                     turns the new policy number into strp_num.  The
                     SYSTR_POLICY_ASSIGN operation attaches the policy identi-
                     fied by strp_num to strp_pid, with a maximum of
                     strp_maxents entries.  The SYSTR_POLICY_MODIFY operation
                     changes the entry indexed by strp_code to strp_policy.

     STRIOCGETCWD pid_t
                     Set the working directory of the current process to that
                     of the named process.

     STRIOCRESCWD    Restore the working directory of the current process.

FILES
     /dev/systrace  system call tracing facility

SEE ALSO
     ioctl(2), read(2), options(4), securelevel(7)

HISTORY
     The systrace facility first appeared in OpenBSD 3.2.

OpenBSD 3.5                      May 26, 2002                                3
