systrace(4) - NetBSD Manual Pages

SYSTRACE(4)             NetBSD Kernel Interfaces Manual            SYSTRACE(4)


NAME

     systrace - enforce and generate policies for system calls


SYNOPSIS

     options SYSTRACE


DESCRIPTION

     The systrace kernel facility provides a mechanism to manipulate and
     enforce access policies for system calls.  Using the systrace facility it
     is possible to monitor and control a process's access to the kernel
     through system calls.

     Access to the systrace facility is provided to userland processes, such
     as systrace(1), through an ioctl(2) interface on the pseudo-device
     /dev/systrace.  This interface allows messages to be sent from the kernel
     to the userland process to request confirmation of an access policy.

     The systrace facility can assign the following policies to system calls
     for a specific process:

           SYSTR_POLICY_ASK
                   Send a message on /dev/systrace requesting the access pol-
                   icy for the system call.

           SYSTR_POLICY_PERMIT
                   Immediately allow the system call.

           SYSTR_POLICY_NEVER
                   Immediately deny the system call and 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 {
             int32_t 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;
             int16_t 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 {
             int32_t code;
             int32_t argsize;
             register_t args[SYSTR_MAXARGS];
             register_t rval[2];
             int32_t result;
     };

     struct str_msg_child {
             pid_t new_pid;
     };


IOCTL INTERFACE

     The systrace facility supports the following ioctl(2) operations:

     STRIOCATTACH pid_t
             Attach to the process with the specified process ID.  This opera-
             tion will fail under the following conditions:

                   1.  The process is trying to attach to itself.
                   2.  The process is a system process.
                   3.  The process is being traced already.
                   4.  You do not own the process and you are not root.
                   5.  The process is init(8), and the kernel was not compiled
                       with option INSECURE.

     STRIOCDETACH pid_t
             Wake up the process if it is waiting for an answer, and detach
             from it.

     STRIOCANSWER struct systrace_answer
             Notify the systrace facility in response to a SYSTR_MSG_ASK mes-
             sage what to do with a system call that was assigned a policy of
             SYSTR_POLICY_ASK.

             struct systrace_answer {
                     pid_t stra_pid;     /* PID of process being traced */
                     int32_t stra_policy;    /* Policy to assign */
                     int32_t stra_error;     /* Return value of denied syscall
                                            (will return EPERM if zero) */
                     int32_t stra_flags;
             #define SYSTR_FLAGS_RESULT 0x0001    /* Report syscall result */
             };

             Valid return values for stra_policy are SYSTR_POLICY_PERMIT,
             SYSTR_POLICY_ASK and SYSTR_POLICY_NEVER.

     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 */
                     int32_t 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 */
                     int32_t strp_num;
                     union {
                             struct {
                                     int16_t code;
             #define SYSTR_POLICY_ASK        0
             #define SYSTR_POLICY_PERMIT     1
             #define SYSTR_POLICY_NEVER      2
                                     int16_t policy;
                             } assign;
                             pid_t pid;
                             int32_t 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 returns the new pol-
             icy number into strp_num.  The SYSTR_POLICY_ASSIGN operation
             attaches the policy identified by strp_num to strp_pid, with a
             maximum of strp_maxents entries.  The SYSTR_POLICY_MODIFY opera-
             tion 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
             specified process.

     STRIOCRESCWD
             Restore the working directory of the current process.


FILES

     /dev/systrace  system call tracing facility


SEE ALSO

     systrace(1), ioctl(2), read(2), options(4), init(8)


HISTORY

     The systrace facility first appeared in OpenBSD 3.2, and then in
     NetBSD 2.0.

NetBSD 2.0                       July 14, 2003                      NetBSD 2.0