Fix possible lockup in an atexit handler

* src/estream.c (_gpgrt_fflush): Add arg in_atexit and skip the flush in
  this mode if the lock can not be taken.  Change all callers.
--

The problem should up with gpgsm encryption on the standard mode and a
no public key error.  In this case the process got stuck in the atexit
handler after a FAILURE gpgsm-exit status line to stderr.  It is
better not to have a hanging process than having flushed everything.

5 files changed, 24 insertions, 9 deletions

diff --git a/src/argparse.c b/src/argparse.c
index 9868fa7..0cf0083 100644
--- a/src/argparse.c
+++ b/src/argparse.c
@@ -250,7 +250,7 @@ flushstrings (int is_error)
   if (custom_outfnc)
     custom_outfnc (is_error? 2:1, NULL);
   else
-    _gpgrt_fflush (is_error? es_stderr : es_stdout);
+    _gpgrt_fflush (is_error? es_stderr : es_stdout, 0);
 }
 
 
diff --git a/src/b64enc.c b/src/b64enc.c
index a4edd0c..b25753c 100644
--- a/src/b64enc.c
+++ b/src/b64enc.c
@@ -202,7 +202,7 @@ _gpgrt_b64enc_write (gpgrt_b64state_t state, const void *buffer, size_t nbytes)
   if (!nbytes)
     {
       if (buffer)
-        if (_gpgrt_fflush (state->stream))
+        if (_gpgrt_fflush (state->stream, 0))
           goto write_error;
       return 0;
     }
diff --git a/src/estream.c b/src/estream.c
index 4bf3bd3..55709f8 100644
--- a/src/estream.c
+++ b/src/estream.c
@@ -599,7 +599,7 @@ static void
 do_deinit (void)
 {
   /* Flush all streams. */
-  _gpgrt_fflush (NULL);
+  _gpgrt_fflush (NULL, 1); /* 1 = we are in an atexit handler */
 
   /* We should release the estream_list.  However there is one
      problem: That list is also used to search for the standard
@@ -4552,8 +4552,9 @@ do_fflush (estream_t stream)
 }
 
 
+/* IN_ATEXIT is set when this function is called by an atexit handler.  */
 int
-_gpgrt_fflush (estream_t stream)
+_gpgrt_fflush (estream_t stream, int in_atexit)
 {
   int err;
 
@@ -4572,9 +4573,23 @@ _gpgrt_fflush (estream_t stream)
       for (item = estream_list; item; item = item->next)
         if (item->stream)
           {
-            lock_stream (item->stream);
-            err |= do_fflush (item->stream);
-            unlock_stream (item->stream);
+            if (in_atexit)
+              {
+                /* Do not flush if we can't take the lock while we are
+                 * in an atexit handler.  The atexit handler might
+                 * have been called while the stream was locked. */
+                if (!trylock_stream (item->stream))
+                  {
+                    err |= do_fflush (item->stream);
+                    unlock_stream (item->stream);
+                  }
+              }
+            else
+              {
+                lock_stream (item->stream);
+                err |= do_fflush (item->stream);
+                unlock_stream (item->stream);
+              }
           }
       unlock_list ();
     }
diff --git a/src/gpgrt-int.h b/src/gpgrt-int.h
index d373435..b8533dc 100644
--- a/src/gpgrt-int.h
+++ b/src/gpgrt-int.h
@@ -377,7 +377,7 @@ void _gpgrt_clearerr_unlocked (gpgrt_stream_t stream);
 int _gpgrt__pending (gpgrt_stream_t stream);
 int _gpgrt__pending_unlocked (gpgrt_stream_t stream);
 
-int _gpgrt_fflush (gpgrt_stream_t stream);
+int _gpgrt_fflush (gpgrt_stream_t stream, int in_atexit);
 int _gpgrt_fseek (gpgrt_stream_t stream, long int offset, int whence);
 int _gpgrt_fseeko (gpgrt_stream_t stream, gpgrt_off_t offset, int whence);
 long int _gpgrt_ftell (gpgrt_stream_t stream);
diff --git a/src/visibility.c b/src/visibility.c
index 98d4721..5574f33 100644
--- a/src/visibility.c
+++ b/src/visibility.c
@@ -374,7 +374,7 @@ gpgrt_clearerr_unlocked (estream_t stream)
 int
 gpgrt_fflush (estream_t stream)
 {
-  return _gpgrt_fflush (stream);
+  return _gpgrt_fflush (stream, 0);
 }
 
 int