pututxline() proves somewhat troublesome on MacOS X. Implement a few work-arounds to avoid some of these problems.

git-svn-id: https://shellinabox.googlecode.com/svn/trunk@235 0da03de8-d603-11dd-86c2-0f8696b7b6f9

config.h

@@ -174,7 +174,7 @@
 #define STDC_HEADERS 1
 
 /* Most recent revision number in the version control system */
-#define VCS_REVISION "234"
+#define VCS_REVISION "235"
 
 /* Version number of package */
 #define VERSION "2.10"

configure

@@ -2328,7 +2328,7 @@ ac_link='$CC -o conftest$ac_exeext $CFLAGS $CPPFLAGS $LDFLAGS conftest.$ac_ext $
 ac_compiler_gnu=$ac_cv_c_compiler_gnu
 
 
-VCS_REVISION=234
+VCS_REVISION=235
 
 
 cat >>confdefs.h <<_ACEOF

configure.ac

@@ -2,7 +2,7 @@ AC_PREREQ(2.57)
 
 dnl This is the one location where the authoritative version number is stored
 AC_INIT(shellinabox, 2.10, markus@shellinabox.com)
-VCS_REVISION=234
+VCS_REVISION=235
 AC_SUBST(VCS_REVISION)
 AC_DEFINE_UNQUOTED(VCS_REVISION, "${VCS_REVISION}",
                    [Most recent revision number in the version control system])

demo/vt100.js

@@ -2402,7 +2402,7 @@ VT100.prototype.toggleCursorBlinking = function() {
 };
 
 VT100.prototype.about = function() {
-  alert("VT100 Terminal Emulator " + "2.10 (revision 234)" +
+  alert("VT100 Terminal Emulator " + "2.10 (revision 235)" +
         "\nCopyright 2008-2010 by Markus Gutschke\n" +
         "For more information check http://shellinabox.com");
 };

shellinabox/launcher.c

@@ -167,6 +167,9 @@ static int (*x_misc_conv)(int, const struct pam_message **,
 #define misc_conv             x_misc_conv
 #endif
 
+static int   launcher = -1;
+static uid_t restricted;
+
 // MacOS X has a somewhat unusual definition of getgrouplist() which can
 // trigger a compile warning.
 #if defined(HAVE_GETGROUPLIST_TAKES_INTS)
@@ -177,9 +180,82 @@ static int x_getgrouplist(const char *user, gid_t group,
 #define getgrouplist x_getgrouplist
 #endif
 
-static int   launcher = -1;
-static uid_t restricted;
+// BSD systems have special requirements on how utmp entries have to be filled
+// out in order to be updated by non-privileged users. In particular, they
+// want the real user name in the utmp recode.
+// This all wouldn't be so bad, if pututxline() wouldn't print an error message
+// to stderr, if it fails to run. Unfortunately, it has been observed to do so.
+// That means, we need to jump through some hoops to intercept these messages.
+#ifdef HAVE_UTMPX_H
+struct utmpx *x_pututxline(struct utmpx *ut) {
+  // N.B. changing global file descriptors isn't thread safe. But all call
+  // sites are guaranteed to be single-threaded. If that ever changes, this
+  // code will need rewriting.
+  int oldStdin         = dup(0);
+  int oldStdout        = dup(1);
+  int oldStderr        = dup(2);
+  check(oldStdin > 2 && oldStdout > 2 && oldStderr > 2);
+  int nullFd           = open("/dev/null", O_RDWR);
+  check(nullFd > 2);
+  check(dup2(nullFd, 0) == 0);
+  NOINTR(close(nullFd));
 
+  // Set up a pipe so that we can read error messages that might be printed
+  // to stderr. We assume that the kernel maintains a buffer that is
+  // sufficiently large to receive the bytes written to it without causing
+  // the I/O operation to block.
+  int fds[2];
+  check(!pipe(fds));
+  check(dup2(fds[1], 1) == 1);
+  check(dup2(fds[1], 2) == 2);
+  NOINTR(close(fds[1]));
+  struct utmpx *ret    = pututxline(ut);
+  int err              = ret == NULL;
+
+  // Close the write end of the pipe, so that we can read until EOF.
+  check(dup2(0, 1) == 1);
+  check(dup2(0, 2) == 2);
+  char buf[128];
+  while (NOINTR(read(fds[0], buf, sizeof(buf))) > 0) {
+    err                = 1;
+  }
+  NOINTR(close(fds[0]));
+
+  // If we either received an error from pututxline() or if we saw an error
+  // message being written out, adjust the utmp record and retry.
+  if (err) {
+    uid_t uid          = getuid();
+    if (uid) {
+      // We only retry if the code is not running as root. Otherwise, fixing
+      // the utmp record is unlikely to do anything for us.
+      // If running as non-root, we set the actual user name in the utmp
+      // record. This is not ideal, but if it allows us to update the record
+      // then that's the best we do.
+      const char *user = getUserName(uid);
+      if (user) {
+        memset(&ut->ut_user[0], 0, sizeof(ut->ut_user));
+        strncat(&ut->ut_user[0], user, sizeof(ut->ut_user));
+        ret            = pututxline(ut);
+        free((char *)user);
+      }
+    }
+  }
+
+  // Clean up. Reset file descriptors back to their original values.
+  check(dup2(oldStderr, 2) == 2);
+  check(dup2(oldStdout, 1) == 1);
+  check(dup2(oldStdin,  0) == 0);
+  NOINTR(close(oldStdin));
+  NOINTR(close(oldStdout));
+  NOINTR(close(oldStderr));
+
+  // It is quite likely that we won't always be in a situation to update the
+  // system's utmp records. Return a non-fatal error to the caller.
+
+  return ret;
+}
+#define pututxline x_pututxline
+#endif
 
 // If the PAM misc library cannot be found, we have to provide our own basic
 // conversation function. As we know that this code is only ever called from
@@ -1491,6 +1567,9 @@ static void launcherDaemon(int fd) {
   sa.sa_sigaction             = sigChildHandler;
   check(!sigaction(SIGCHLD, &sa, NULL));
 
+  // pututxline() can cause spurious SIGHUP signals. Better ignore those.
+  signal(SIGHUP, SIG_IGN);
+
   struct LaunchRequest request;
   for (;;) {
     errno                     = 0;

shellinabox/shell_in_a_box.js

@@ -358,7 +358,7 @@ ShellInABox.prototype.extendContextMenu = function(entries, actions) {
 };
 
 ShellInABox.prototype.about = function() {
-  alert("Shell In A Box version " + "2.10 (revision 234)" +
+  alert("Shell In A Box version " + "2.10 (revision 235)" +
         "\nCopyright 2008-2010 by Markus Gutschke\n" +
         "For more information check http://shellinabox.com" +
         (typeof serverSupportsSSL != 'undefined' && serverSupportsSSL ?

shellinabox/vt100.js

@@ -2402,7 +2402,7 @@ VT100.prototype.toggleCursorBlinking = function() {
 };
 
 VT100.prototype.about = function() {
-  alert("VT100 Terminal Emulator " + "2.10 (revision 234)" +
+  alert("VT100 Terminal Emulator " + "2.10 (revision 235)" +
         "\nCopyright 2008-2010 by Markus Gutschke\n" +
         "For more information check http://shellinabox.com");
 };