[chrony-dev] [PATCH] Privilege Separation - Version 3 - Add helper process

[Bryan Christianson <bryan@xxxxxxxxxxxxx>]

Privileged helper that will perform adjtime(), settimeofday(), bind() on
behalf of chronyd when running as non-root user.

Changes since version 2
1. All PRIVOPS_xxxx conditional compilation defines to be declared in the configure script
2. File decriptor transfer is merged with sending/receiving request/response
3. Helper functions receive contents of request union directly from helper_main()
4. Reorder switch in helper_main()
5. Close IPC file descriptor and exit from helper_main (previously helper_main returned to its caller).
6. Explicitly include <sys/wait.h> rather than rely on implicit inclusion
---
 logging.h |   1 +
 privops.c | 487 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 privops.h |  54 +++++++
 sysincl.h |   1 +
 4 files changed, 543 insertions(+)
 create mode 100644 privops.c
 create mode 100644 privops.h

diff --git a/logging.h b/logging.h
index b480c42..8fc8640 100644
--- a/logging.h
+++ b/logging.h
@@ -100,6 +100,7 @@ typedef enum {
   LOGF_Keys,
   LOGF_Logging,
   LOGF_Nameserv,
+  LOGF_PrivOps,
   LOGF_Rtc,
   LOGF_Regress,
   LOGF_Sys,
diff --git a/privops.c b/privops.c
new file mode 100644
index 0000000..d2dbace
--- /dev/null
+++ b/privops.c
@@ -0,0 +1,487 @@
+/*
+  chronyd/chronyc - Programs for keeping computer clocks accurate.
+
+ **********************************************************************
+ * Copyright (C) Bryan Christianson 2015
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of version 2 of the GNU General Public License as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+ *
+ **********************************************************************
+
+  =======================================================================
+
+  Perform privileged operations over a unix socket to a privileged fork.
+
+*/
+#include "config.h"
+
+#include "sysincl.h"
+#include "conf.h"
+#include "logging.h"
+#include "privops.h"
+#include "util.h"
+
+#define op_ADJTIME        1024
+#define op_SETTIMEOFDAY   1025
+#define op_BINDSOCKET     1026
+
+union sockaddr_in46 {
+  struct sockaddr_in in4;
+#ifdef FEAT_IPV6
+  struct sockaddr_in6 in6;
+#endif
+  struct sockaddr u;
+};
+
+/* daemon request structs */
+
+typedef struct {
+  struct timeval tv;
+} ReqAdjustTime;
+
+typedef struct {
+  struct timeval tv;
+} ReqSetTime;
+
+typedef struct {
+  int sock;
+  socklen_t sa_len;
+  union sockaddr_in46 sa;
+} ReqBindSocket;
+
+typedef struct {
+  int op;
+  union {
+    ReqAdjustTime adj_tv;
+    ReqSetTime settime_tv;
+    ReqBindSocket bind_sock;
+  } u;
+} PrvRequest;
+
+/* helper response structs */
+
+typedef struct {
+  struct timeval tv;
+} ResAdjustTime;
+
+typedef struct {
+  char msg[256];
+} ResFatalMsg;
+
+typedef struct {
+  int fatal_error;
+  int rc;
+  int res_errno;
+  union {
+    ResFatalMsg fatal_msg;
+    ResAdjustTime adj_tv;
+  } u;
+} PrvResponse;
+
+static int helper_fd = -1;
+
+static int
+have_helper(void)
+{
+  return helper_fd >= 0;
+}
+
+/* ======================================================================= */
+
+/* HELPER - prepare fatal error for daemon */
+static void
+res_fatal(PrvResponse *res, const char *fmt, ...)
+{
+  va_list ap;
+  va_start(ap, fmt);
+
+  memset(res, 0, sizeof(PrvResponse));
+  res->fatal_error = 1;
+  vsnprintf(res->u.fatal_msg.msg, sizeof(ResFatalMsg), fmt, ap);
+
+  va_end(ap);
+}
+
+/* ======================================================================= */
+
+/* HELPER - send response to the fd */
+
+static int
+send_response(int fd, const PrvResponse *res)
+{
+  if (write(fd, res, sizeof(PrvResponse)) != sizeof(PrvResponse))
+    return -1;
+
+  return 0;
+}
+
+/* ======================================================================= */
+/* receive daemon request plus optional file descriptor over a unix socket */
+
+static int
+receive_from_daemon(int fd, PrvRequest *req)
+{
+  int data_bytes;
+  struct msghdr msg;
+  struct cmsghdr *cmsg;
+  struct iovec iov;
+  char cmsgbuf[256];
+
+  iov.iov_base = req;
+  iov.iov_len = sizeof(PrvRequest);
+
+  msg.msg_name = NULL;
+  msg.msg_namelen = 0;
+  msg.msg_iov = &iov;
+  msg.msg_iovlen = 1;
+  msg.msg_control = (void *)cmsgbuf;
+  msg.msg_controllen = sizeof(cmsgbuf);
+  msg.msg_flags = MSG_WAITALL;
+
+  /* read the data */
+  data_bytes = recvmsg(fd, &msg, 0);
+  if (data_bytes <= 0)
+    return -1;
+
+  if (req->op == op_BINDSOCKET) {
+    /* extract transferred descriptor */
+    for (cmsg = CMSG_FIRSTHDR(&msg); cmsg; cmsg = CMSG_NXTHDR(&msg, cmsg)) {
+      if (cmsg->cmsg_level == SOL_SOCKET && cmsg->cmsg_type == SCM_RIGHTS)
+        memcpy(&req->u.bind_sock.sock, CMSG_DATA(cmsg), sizeof(int));
+    }
+  }
+
+  return data_bytes;
+}
+
+/* ======================================================================= */
+
+/* HELPER - perform adjtime() */
+
+static void
+do_adjtime(const ReqAdjustTime *req, PrvResponse *res)
+{
+  const struct timeval *delta = &req->tv;
+  struct timeval olddelta;
+
+  res->rc = adjtime(delta, &olddelta);
+  if (res->rc != 0)
+    res->res_errno = errno;
+  else
+    res->u.adj_tv.tv = olddelta;
+}
+
+/* ======================================================================= */
+
+/* HELPER - perform settimeofday() */
+
+static void
+do_settimeofday(const ReqSetTime *req, PrvResponse *res)
+{
+  const struct timeval *tv = &req->tv;
+
+  res->rc = settimeofday(tv, NULL);
+  if (res->rc != 0)
+    res->res_errno = errno;
+}
+
+/* ======================================================================= */
+
+/* HELPER - bind port to a socket */
+static void
+do_bindsocket(ReqBindSocket *req, PrvResponse *res)
+{
+  unsigned short port;
+  IPAddr ip;
+  int sock_fd;
+  struct sockaddr *sa;
+  socklen_t sa_len;
+
+  sa = &req->sa.u;
+  sa_len = req->sa_len;
+  sock_fd = req->sock;
+
+  UTI_SockaddrToIPAndPort(sa, &ip, &port);
+  if (port != 0 && port != CNF_GetNTPPort()) {
+    res_fatal(res, "PRV_BindSocket, invalid port: %d", port);
+    return;
+  }
+
+  res->rc = bind(sock_fd, sa, sa_len);
+  if (res->rc != 0)
+    res->res_errno = errno;
+
+  /* sock is still open on daemon side  but we're done with it in the helper */
+  close(sock_fd);
+}
+
+/* ======================================================================= */
+
+/* HELPER - main loop - action requests from the daemon */
+
+static void
+helper_main(int fd)
+{
+  PrvRequest req;
+  PrvResponse res;
+
+  while (1) {
+    if (receive_from_daemon(fd, &req) < sizeof(PrvRequest))
+      /* read error or closed input - we cannot recover - give up */
+      break;
+
+    memset(&res, 0, sizeof(PrvResponse));
+    switch (req.op) {
+    case op_ADJTIME:
+      do_adjtime(&req.u.adj_tv, &res);
+      break;
+
+    case op_SETTIMEOFDAY:
+      do_settimeofday(&req.u.settime_tv, &res);
+      break;
+
+    case op_BINDSOCKET:
+      do_bindsocket(&req.u.bind_sock, &res);
+      break;
+
+    default:
+      res_fatal(&res, "Unexpected operator : %d", req.op);
+      break;
+    }
+    send_response(fd, &res);
+  }
+
+  close(fd);
+  exit(0);
+}
+
+/* ======================================================================= */
+
+/* DAEMON - read helper response from fd */
+
+static int
+read_response(int fd, PrvResponse *res)
+{
+  if (read(fd, res, sizeof(PrvResponse)) < sizeof(PrvResponse))
+    LOG_FATAL(LOGF_PrivOps, "Error reading from helper fd : %s", strerror(errno));
+
+  if (res->fatal_error)
+    LOG_FATAL(LOGF_PrivOps, "Fatal error in helper: %s", res->u.fatal_msg.msg);
+
+  /* if operation failed in the helper, set errno so daemon can print log message */
+  if (res->rc != 0) {
+    errno = res->res_errno;
+    return -1;
+  }
+  return 0;
+}
+
+/* ======================================================================= */
+
+/* DAEMON - send daemon request to fd and wait for response */
+
+static int
+send_to_helper(int fd, PrvRequest *req, PrvResponse *res)
+{
+  struct msghdr msg;
+  struct iovec iov;
+  char cmsgbuf[256];
+
+  iov.iov_base = req;
+  iov.iov_len = sizeof(PrvRequest);
+
+  msg.msg_name = NULL;
+  msg.msg_namelen = 0;
+  msg.msg_iov = &iov;
+  msg.msg_iovlen = 1;
+  msg.msg_control = NULL;
+  msg.msg_controllen = 0;
+  msg.msg_flags = 0;
+
+  if (req->op == op_BINDSOCKET) {
+    /* send file descriptor as a control message */
+    int *ptr_send_fd;
+    int cmsglen;
+    struct cmsghdr *cmsg;
+
+    cmsglen = 0;
+
+    msg.msg_control = cmsgbuf;
+    msg.msg_controllen = sizeof(cmsgbuf);
+
+    cmsg = CMSG_FIRSTHDR(&msg);
+    memset(cmsg, 0, CMSG_SPACE(sizeof(int)));
+    cmsglen += CMSG_SPACE(sizeof(int));
+
+    cmsg->cmsg_level = SOL_SOCKET;
+    cmsg->cmsg_type = SCM_RIGHTS;
+    cmsg->cmsg_len = CMSG_LEN(sizeof(int));
+
+    ptr_send_fd = (int *)CMSG_DATA(cmsg);
+    *ptr_send_fd = req->u.bind_sock.sock;
+
+    msg.msg_controllen = cmsglen;
+  }
+
+  if (sendmsg(fd, &msg, 0) != sizeof(PrvRequest))
+      LOG_FATAL(LOGF_PrivOps, "Error writing to helper fd : %s", strerror(errno));
+
+  return read_response(fd, res);
+}
+
+/* ======================================================================= */
+
+/* DAEMON - bind socket to reserved port */
+
+#if defined(PRIVOPS_BINDSOCKET)
+int
+PRV_BindSocket(int sock, struct sockaddr *address, socklen_t address_len)
+{
+  PrvRequest req;
+  PrvResponse res;
+  IPAddr ip;
+  unsigned short port;
+
+  UTI_SockaddrToIPAndPort(address, &ip, &port);
+  if (port != 0 && port != CNF_GetNTPPort())
+    LOG_FATAL(LOGF_PrivOps, "PRV_BindSocket, invalid port: %d", port);
+
+  if (!have_helper())
+    /* dont use the helper if not required */
+    return bind(sock, address, address_len);
+
+  req.op = op_BINDSOCKET;
+  req.u.bind_sock.sock = sock;
+  req.u.bind_sock.sa_len = address_len;
+  memcpy(&req.u.bind_sock.sa.u, address, address_len);
+
+  if (send_to_helper(helper_fd, &req, &res) != 0)
+    return -1;
+
+  return 0;
+}
+#endif
+
+/* ======================================================================= */
+
+/* DAEMON - request adjtime() */
+
+#if defined(PRIVOPS_ADJUSTTIME)
+int
+PRV_AdjustTime(const struct timeval *delta, struct timeval *olddelta)
+{
+  PrvRequest req;
+  PrvResponse res;
+
+  if (!have_helper() || delta == NULL)
+    /* helper is not running or read adjustment call */
+    return adjtime(delta, olddelta);
+
+  req.op = op_ADJTIME;
+  req.u.adj_tv.tv = *delta;
+
+  if (send_to_helper(helper_fd, &req, &res) != 0)
+    return -1;
+
+  if (olddelta)
+    *olddelta = res.u.adj_tv.tv;
+
+  return 0;
+}
+#endif
+
+/* ======================================================================= */
+
+/* DAEMON - request settimeofday() */
+
+#if defined(PRIVOPS_SETTIME)
+int
+PRV_SetTime(const struct timeval *tp, const struct timezone *tzp)
+{
+  PrvRequest req;
+  PrvResponse res;
+
+  /* only support setting the time */
+  assert(tp != NULL);
+  assert(tzp == NULL);
+
+  if (!have_helper()) {
+    /* helper is not running - this will fail if not privileged */
+    return settimeofday(tp, NULL);
+  }
+
+  req.op = op_SETTIMEOFDAY;
+  req.u.settime_tv.tv = *tp;
+
+  return send_to_helper(helper_fd, &req, &res);
+}
+#endif
+
+/* ======================================================================= */
+
+/* DAEMON - setup socket(s) then fork to run the helper */
+/* must be called before privileges are dropped */
+
+void
+PRV_Initialise(void)
+{
+  pid_t pid;
+  int sock_pair[2];
+
+  if (have_helper())
+    LOG_FATAL(LOGF_PrivOps, "PRV_start, helper is already running");
+
+  if (socketpair(AF_UNIX, SOCK_DGRAM, 0, sock_pair) != 0)
+    LOG_FATAL(LOGF_PrivOps, "PRV_start, socketpair() failed : %s", strerror(errno));
+
+  UTI_FdSetCloexec(sock_pair[0]);
+  UTI_FdSetCloexec(sock_pair[1]);
+
+  pid = fork();
+  if (pid == -1)
+    LOG_FATAL(LOGF_PrivOps, "PRV_start, fork failed : %s", strerror(errno));
+
+  if (pid == 0) {
+    /* child process */
+    int fd;
+    close(sock_pair[0]);
+
+    /* close other descriptors inherited from the parent process */
+    for (fd = 0; fd < 1024; fd++) {
+      if (fd != sock_pair[1])
+        close(fd);
+    }
+
+    helper_main(sock_pair[1]);
+
+  } else {
+    /* parent process */
+    close(sock_pair[1]);
+    helper_fd = sock_pair[0];
+  }
+}
+
+/* ======================================================================= */
+
+/* DAEMON - graceful shutdown of the helper */
+
+void
+PRV_Finalise(void)
+{
+  int status;
+  close(helper_fd);
+  helper_fd = -1;
+  wait(&status);
+}
+
diff --git a/privops.h b/privops.h
new file mode 100644
index 0000000..b56ebcf
--- /dev/null
+++ b/privops.h
@@ -0,0 +1,54 @@
+/*
+  chronyd/chronyc - Programs for keeping computer clocks accurate.
+
+ **********************************************************************
+ * Copyright (C) Bryan Christianson 2015
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of version 2 of the GNU General Public License as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+ *
+ **********************************************************************
+
+  =======================================================================
+
+  Perform privileged operations over a unix socket to a privileged fork.
+
+*/
+
+#ifndef GOT_PRIVOPS_H
+#define GOT_PRIVOPS_H
+
+#if defined(PRIVOPS_ADJUSTTIME)
+  int PRV_AdjustTime(const struct timeval *delta, struct timeval *olddelta);
+#else
+  #define PRV_AdjustTime adjtime
+#endif
+
+#if defined(PRIVOPS_BINDSOCKET)
+  int PRV_BindSocket(int sock, struct sockaddr *address, socklen_t address_len);
+#else
+  #define PRV_BindSocket bind
+#endif
+
+#if defined(PRIVOPS_SETTIME)
+  int PRV_SetTime(const struct timeval *tp, const struct timezone *tzp);
+#else
+  #define PRV_SetTime settimeofday
+#endif
+
+#if defined(PRIVOPS_HELPER)
+  void PRV_Initialise(void);
+  void PRV_Finalise(void);
+#endif
+
+#endif
diff --git a/sysincl.h b/sysincl.h
index 30e9b48..7dbc8f2 100644
--- a/sysincl.h
+++ b/sysincl.h
@@ -53,6 +53,7 @@
 #include <sys/types.h>
 #include <sys/un.h>
 #include <sys/shm.h>
+#include <sys/wait.h>
 #include <syslog.h>
 #include <time.h>
 #include <unistd.h>
-- 
2.4.9 (Apple Git-60)


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