diff -up ntp-4.2.6p5/html/drivers/driver28.html.shmperm ntp-4.2.6p5/html/drivers/driver28.html
--- ntp-4.2.6p5/html/drivers/driver28.html.shmperm 2009-12-09 08:36:37.000000000 +0100
+++ ntp-4.2.6p5/html/drivers/driver28.html 2015-02-09 15:57:57.450877311 +0100
@@ -18,7 +18,8 @@
Driver ID: <tt>SHM</tt></p>
<h4>Description</h4>
- <p>This driver receives its reference clock info from a shared memory-segment. The shared memory-segment is created with owner-only access for unit 0 and 1, and world access for unit 2 and 3</p>
+ <p>This driver receives its reference clock info from a shared memory-segment. The shared memory-segment is created with owner-only access for unit 0 and 1, and world access for other units unless the mode word is set for owner-only access.</p>
+
<h4>Structure of shared memory-segment</h4>
<pre>struct shmTime {
@@ -94,6 +95,40 @@ Here is a sample showing the GPS recepti
54364 85700.160 127.127.28.0 65 0 65 0 0
</pre>
+ <h4>The 'mode' word</h4>
+
+ <p>
+ Some aspects of the driver behavior can be adjusted by setting bits of
+ the 'mode' word in the server configuration line:<br>
+ <tt>server 127.127.28.</tt><i>x</i><tt> mode </tt><i>Y</i>
+ </p>
+
+ <table border="1" width="100%">
+ <caption>mode word bits and bit groups</caption>
+ <tbody><tr>
+ <th align="center">Bit</th>
+ <th align="center">Dec</th>
+ <th align="center">Hex</th>
+ <th align="left">Meaning</th>
+ </tr>
+
+ <tr>
+ <td align="center">0</td>
+ <td align="center">1</td>
+ <td align="center">1</td>
+ <td>The SHM segment is private (mode 0600). This is the fixed
+ default for clock units 0 and 1; clock units >1 are mode
+ 0666 unless this bit is set for the specific unit.</td>
+
+ </tr><tr>
+ <td align="center">1-31</td>
+ <td align="center">-</td>
+ <td align="center">-</td>
+ <td><i>reserved -- do not use</i></td>
+ </tr>
+ </tbody>
+ </table>
+
<h4>Fudge Factors</h4>
<dl>
<dt><tt>time1 <i>time</i></tt>
@@ -112,9 +147,64 @@ Here is a sample showing the GPS recepti
<dd>Not used by this driver.
<dt><tt>flag4 0 | 1</tt>
<dd>If flag4 is set, clockstats records will be written when the driver is polled.
- <h4>Additional Information</h4>
- <p><a href="../refclock.html">Reference Clock Drivers</a></p>
</dl>
+
+ <h4>Public vs. Private SHM segments</h4>
+
+ <p>The driver attempts to create a shared memory segment with an
+ identifier depending on the unit number. This identifier (which can be
+ a numeric value or a string) clearly depends on the method used, which
+ in turn depends on the host operating system:</p>
+
+ <ul>
+ <li><p>
+ <tt>Windows</tt> uses a file mapping to the page file with the
+ name '<tt>Global\NTP</tt><i>u</i>' for public accessible
+ mappings, where <i>u</i> is the clock unit. Private /
+ non-public mappings are created as
+ '<tt>Local\NTP</tt><i>u</i>'.
+ </p><p>
+ Public access assigns a NULL DACL to the memory mapping, while
+ private access just uses the default DACL of the process creating
+ the mapping.
+ </p>
+ </li>
+ <li><p>
+ <tt>SYSV IPC</tt> creates a shared memory segment with a key value
+ of <tt>0x4E545030</tt> + <i>u</i>, where <i>u</i> is again
+ the clock unit. (This value could be hex-decoded as 'NTP0',
+ 'NTP1',..., with funny characters for units > 9.)
+ </p><p>
+ Public access means a permission set of 0666, while private access
+ creates the mapping with a permission set of 0600.
+ </p>
+ </li>
+ </ul>
+
+ <p>There's no support for POSIX shared memory yet.</p>
+
+ <p><i>NTPD</i> is started as root on most POSIX-like operating systems
+ and uses the setuid/setgid system API to run under reduced rights once
+ the initial setup of the process is done. One consequence out of this
+ is that the allocation of SHM segments must be done early during the
+ clock setup. The actual polling of the clock is done as the run-time
+ user; deferring the creation of the SHM segment to this point will
+ create a SHM segment owned by the runtime-user account. The internal
+ structure of <i>NTPD</i> does not permit the use of a fudge flag if
+ this is to be avoided; this is the reason why a mode bit is used for
+ the configuration of a public segment.
+ </p>
+
+ <p>When running under Windows, the chosen user account must be able to
+ create a SHM segment in the global object name space for SHM clocks with
+ public access. Otherwise the session isolation used by Windows kernels
+ after WinXP will get into the way if the client program does not run in
+ the same session.
+ </p>
+
+ <h4>Additional Information</h4>
+ <p><a href="../refclock.html">Reference Clock Drivers</a></p>
+
<hr>
<script type="text/javascript" language="javascript" src="scripts/footer.txt"></script>
</body>
diff -up ntp-4.2.6p5/ntpd/refclock_shm.c.shmperm ntp-4.2.6p5/ntpd/refclock_shm.c
--- ntp-4.2.6p5/ntpd/refclock_shm.c.shmperm 2015-02-09 15:52:06.131877933 +0100
+++ ntp-4.2.6p5/ntpd/refclock_shm.c 2015-02-09 15:52:06.137877933 +0100
@@ -52,6 +52,11 @@
#define NSAMPLES 3 /* stages of median filter */
/*
+ * Mode flags
+ */
+#define SHM_MODE_PRIVATE 0x0001
+
+/*
* Function prototypes
*/
static int shm_start (int unit, struct peer *peer);
@@ -99,6 +104,7 @@ struct shmTime {
struct shmunit {
struct shmTime *shm; /* pointer to shared memory segment */
+ int forall; /* access for all UIDs? */
/* debugging/monitoring counters - reset when printed */
int ticks; /* number of attempts to read data*/
@@ -109,9 +115,12 @@ struct shmunit {
};
-struct shmTime *getShmTime(int);
-
-struct shmTime *getShmTime (int unit) {
+static struct shmTime*
+getShmTime(
+ int unit,
+ int/*BOOL*/ forall
+ )
+{
#ifndef SYS_WINNT
int shmid=0;
@@ -119,8 +128,8 @@ struct shmTime *getShmTime (int unit) {
* Big units will give non-ascii but that's OK
* as long as everybody does it the same way.
*/
- shmid=shmget (0x4e545030+unit, sizeof (struct shmTime),
- IPC_CREAT|(unit<2?0600:0666));
+ shmid=shmget(0x4e545030 + unit, sizeof (struct shmTime),
+ IPC_CREAT | (forall ? 0666 : 0600));
if (shmid==-1) { /*error */
msyslog(LOG_ERR,"SHM shmget (unit %d): %s",unit,strerror(errno));
return 0;
@@ -199,7 +208,9 @@ shm_start(
memset(up, 0, sizeof(*up));
pp->unitptr = (caddr_t)up;
- up->shm = getShmTime(unit);
+ up->forall = (unit >= 2) && !(peer->ttl & SHM_MODE_PRIVATE);
+
+ up->shm = getShmTime(unit, up->forall);
/*
* Initialize miscellaneous peer variables
@@ -314,7 +325,7 @@ int shm_peek(
if (up->shm == 0) {
/* try to map again - this may succeed if meanwhile some-
body has ipcrm'ed the old (unaccessible) shared mem segment */
- up->shm = getShmTime(unit);
+ up->shm = getShmTime(unit, up->forall);
}
shm = up->shm;
if (shm == 0) {