freebsd: add capsicum sandbox

Add support for capsicum on freebsd:

    EPCAP_SANDBOX=capsicum rebar3 do clean, compile, ct

This change adds some ifdef's to use process descriptors (why don't all
unix'es support process descriptors? looking at you linux) because after
capability mode is entered the supervisor process will not be able to
signal the child process by PID.

c_src/epcap.c

@@ -32,6 +32,11 @@
 #include <stdint.h>
 #include <ei.h>
 
+#ifdef EPCAP_SANDBOX_capsicum
+#include <sys/param.h>
+#include <sys/procdesc.h>
+#endif
+
 #include "epcap.h"
 
 static int epcap_open(EPCAP_STATE *);
@@ -57,7 +62,6 @@ main(int argc, char *argv[])
     int ch = 0;
     int fd = 0;
 
-
     ep = calloc(1, sizeof(EPCAP_STATE));
 
     if (ep == NULL)
@@ -188,7 +192,12 @@ main(int argc, char *argv[])
 
     signal(SIGCHLD, gotsig);
 
-    switch (pid = fork()) {
+#ifdef EPCAP_SANDBOX_capsicum
+    pid = pdfork(&ep->pdfd, 0);
+#else
+    pid = fork();
+#endif
+    switch (pid) {
         case -1:
             exit(errno);
         case 0:
@@ -220,7 +229,11 @@ main(int argc, char *argv[])
             epcap_send(ep);
 
 CLEANUP:
+#ifdef EPCAP_SANDBOX_capsicum
+            (void)pdkill(ep->pdfd, SIGTERM);
+#else
             (void)kill(pid, SIGTERM);
+#endif
             break;
     }
 
@@ -232,14 +245,53 @@ main(int argc, char *argv[])
 epcap_send(EPCAP_STATE *ep)
 {
     const int fd = STDIN_FILENO;
+    int maxfd = 0;
     ssize_t n = 0;
     unsigned char buf[SNAPLEN] = {0};
     u_int16_t len = 0;
 
+    int rv = 0;
+
     for ( ; ; ) {
+        fd_set rfds;
+
         if (child_exited)
             return;
 
+        FD_ZERO(&rfds);
+        FD_SET(fd, &rfds);
+
+#ifdef EPCAP_SANDBOX_capsicum
+        FD_SET(ep->pdfd, &rfds);
+        maxfd = MAX(fd, ep->pdfd) + 1;
+#else
+        maxfd = fd + 1;
+#endif
+
+        rv = select(maxfd, &rfds, NULL, NULL, NULL);
+
+        switch (rv) {
+            case 0:
+                continue;
+
+            case -1:
+                if (errno == EINTR)
+                    continue;
+
+                return;
+
+            default:
+                break;
+        }
+
+#ifdef EPCAP_SANDBOX_capsicum
+        if (FD_ISSET(ep->pdfd, &rfds))
+            return;
+#endif
+
+        if (!FD_ISSET(fd, &rfds))
+            continue;
+
         n = read_exact(fd, buf, sizeof(len));
 
         if (n != sizeof(len)) {

c_src/epcap.h

@@ -86,6 +86,9 @@ enum {
 
 typedef struct {
     pcap_t *p;          /* pcap handle */
+#ifdef EPCAP_SANDBOX_capsicum
+    int pdfd;           /* process descriptor for pcap process */
+#endif
     int datalink;       /* dlt */
     int opt;            /* options */
     int verbose;        /* debug messages */

c_src/epcap_sandbox_capsicum.c

@@ -0,0 +1,126 @@
+/* Copyright (c) 2017, Michael Santos <michael.santos@gmail.com>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *
+ * 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.
+ *
+ * Neither the name of the author nor the names of its contributors
+ * may be used to endorse or promote products derived from this software
+ * without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "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
+ * COPYRIGHT HOLDER OR CONTRIBUTORS 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.
+ */
+
+#ifdef EPCAP_SANDBOX_capsicum
+
+#include <unistd.h>
+#include <sys/types.h>
+#include <sys/param.h>
+#include <sys/time.h>
+#include <sys/resource.h>
+#include <sys/capability.h>
+
+#include <errno.h>
+
+#include <pcap/pcap.h>
+#include "epcap.h"
+
+    int
+epcap_sandbox_pcap()
+{
+    struct rlimit rl = {0};
+    cap_rights_t policy_read;
+    cap_rights_t policy_null;
+    cap_rights_t policy_write;
+
+    int fd = -1;
+
+    (void)cap_rights_init(&policy_read, CAP_READ, CAP_EVENT);
+    (void)cap_rights_init(&policy_null);
+    (void)cap_rights_init(&policy_write, CAP_WRITE);
+
+    if (cap_rights_limit(STDIN_FILENO, &policy_null) < 0)
+        return -1;
+
+    if (cap_rights_limit(STDOUT_FILENO, &policy_write) < 0)
+        return -1;
+
+    if (cap_rights_limit(STDERR_FILENO, &policy_write) < 0)
+        return -1;
+
+    if (setrlimit(RLIMIT_NPROC, &rl) != 0)
+        return -1;
+
+    if (getrlimit(RLIMIT_NOFILE, &rl) < 0)
+        return -1;
+
+    for (fd = STDERR_FILENO+1; fd < rl.rlim_cur; fd++) {
+        if (fcntl(fd, F_GETFD, 0) < 0)
+            continue;
+
+        if (cap_rights_limit(fd, &policy_read) < 0)
+            return -1;
+    }
+
+    return cap_enter();
+}
+
+    int
+epcap_sandbox_erl()
+{
+    struct rlimit rl = {0};
+    cap_rights_t policy_read;
+    cap_rights_t policy_write;
+    cap_rights_t policy_null;
+
+    int fd = -1;
+
+    (void)cap_rights_init(&policy_read, CAP_READ, CAP_EVENT);
+    (void)cap_rights_init(&policy_write, CAP_WRITE, CAP_EVENT);
+    (void)cap_rights_init(&policy_null);
+
+    if (cap_rights_limit(STDIN_FILENO, &policy_read) < 0)
+        return -1;
+
+    if (cap_rights_limit(STDOUT_FILENO, &policy_null) < 0)
+        return -1;
+
+    if (cap_rights_limit(STDERR_FILENO, &policy_write) < 0)
+        return -1;
+
+    if (setrlimit(RLIMIT_NPROC, &rl) != 0)
+        return -1;
+
+    if (getrlimit(RLIMIT_NOFILE, &rl) < 0)
+        return -1;
+
+    for (fd = STDERR_FILENO+1; fd < rl.rlim_cur; fd++) {
+        if (fcntl(fd, F_GETFD, 0) < 0)
+            continue;
+
+        if (cap_rights_limit(fd, &policy_write) < 0)
+            return -1;
+    }
+
+    return cap_enter();
+}
+#endif