am-utils-6.2-1.git.e03592f0 - fix debug log deadlock

From: Ian Kent <raven@themaw.net>

It's possible (and likely) a SIGCHLD signal can arrive while in syslog(2)
and also attempt log log a message leading to deadlock.
---
 libamu/xutil.c |   38 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 38 insertions(+)

diff --git a/libamu/xutil.c b/libamu/xutil.c
index b3e3a0f..0d9d2ec 100644
--- a/libamu/xutil.c
+++ b/libamu/xutil.c
@@ -420,14 +420,33 @@ debug_option(char *opt)
 void
 dplog(const char *fmt, ...)
 {
+#ifdef HAVE_SIGACTION
+  sigset_t old, chld;
+#else /* not HAVE_SIGACTION */
+  int mask;
+#endif /* not HAVE_SIGACTION */
   va_list ap;
 
+#ifdef HAVE_SIGACTION
+  sigemptyset(&chld);
+  sigaddset(&chld, SIGCHLD);
+#else /* not HAVE_SIGACTION */
+  mask = sigblock(sigmask(SIGCHLD));
+#endif /* not HAVE_SIGACTION */
+
+  sigprocmask(SIG_BLOCK, &chld, &old);
   if (!logfp)
     logfp = stderr;		/* initialize before possible first use */
 
   va_start(ap, fmt);
   real_plog(XLOG_DEBUG, fmt, ap);
   va_end(ap);
+
+#ifdef HAVE_SIGACTION
+  sigprocmask(SIG_SETMASK, &old, NULL);
+#else /* not HAVE_SIGACTION */
+  mask = sigblock(sigmask(SIGCHLD));
+#endif /* not HAVE_SIGACTION */
 }
 #endif /* DEBUG */
 
@@ -435,14 +454,33 @@ dplog(const char *fmt, ...)
 void
 plog(int lvl, const char *fmt, ...)
 {
+#ifdef HAVE_SIGACTION
+  sigset_t old, chld;
+#else /* not HAVE_SIGACTION */
+  int mask;
+#endif /* not HAVE_SIGACTION */
   va_list ap;
 
+#ifdef HAVE_SIGACTION
+  sigemptyset(&chld);
+  sigaddset(&chld, SIGCHLD);
+  sigprocmask(SIG_BLOCK, &chld, &old);
+#else /* not HAVE_SIGACTION */
+  mask = sigblock(sigmask(SIGCHLD));
+#endif /* not HAVE_SIGACTION */
+
   if (!logfp)
     logfp = stderr;		/* initialize before possible first use */
 
   va_start(ap, fmt);
   real_plog(lvl, fmt, ap);
   va_end(ap);
+
+#ifdef HAVE_SIGACTION
+  sigprocmask(SIG_SETMASK, &old, NULL);
+#else /* not HAVE_SIGACTION */
+  sigsetmask(mask);
+#endif /* not HAVE_SIGACTION */
 }