Fix some xgselect-vs-pselect bugs.

This may not fix Bug#17172, but it fixes some bugs discovering
while auditing xgselect.c for that bug.
when one of glib's file descriptors is greater than FDS_LIM.
Treat rfds, wfds, efds consistently, and test G_IO_PRI too.
Clear input masks when pselect returns zero.

2 files changed, 52 insertions, 48 deletions

diff --git a/src/ChangeLog b/src/ChangeLog
index 51861c6ca7d..8ef5dfe9916 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -1,12 +1,11 @@
-2014-04-15  Stefan Monnier  <monnier@iro.umontreal.ca>
-
-        * buffer.c (Foverlays_at): Add argument `sorted'.
-
-2014-04-14  Eli Zaretskii  <eliz@gnu.org>
-
-        * insdel.c (invalidate_buffer_caches): When deleting or replacing
-        text, invalidate the bidi_paragraph_cache upto and including the
-        preceding newline.
+2014-04-15  Paul Eggert  <eggert@penguin.cs.ucla.edu>
+
+        Fix some xgselect-vs-pselect bugs (Bug#17172).
+        This may not fix Bug#17172, but it fixes some bugs discovering
+        while auditing xgselect.c for that bug.
+        when one of glib's file descriptors is greater than FDS_LIM.
+        Treat rfds, wfds, efds consistently, and test G_IO_PRI too.
+        Clear input masks when pselect returns zero.
 
 2014-04-13  Paul Eggert  <eggert@cs.ucla.edu>
 
diff --git a/src/xgselect.c b/src/xgselect.c
index 1d3f916c9f8..7decca34edf 100644
--- a/src/xgselect.c
+++ b/src/xgselect.c
@@ -33,16 +33,15 @@ int
 xg_select (int fds_lim, fd_set *rfds, fd_set *wfds, fd_set *efds,
            struct timespec const *timeout, sigset_t const *sigmask)
 {
-  fd_set all_rfds, all_wfds;
+  fd_set all_rfds, all_wfds, all_efds;
   struct timespec tmo;
   struct timespec const *tmop = timeout;
 
   GMainContext *context;
-  int have_wfds = wfds != NULL;
   GPollFD gfds_buf[128];
   GPollFD *gfds = gfds_buf;
   int gfds_size = sizeof gfds_buf / sizeof *gfds_buf;
-  int n_gfds, retval = 0, our_fds = 0, max_fds = fds_lim - 1;
+  int n_gfds, retval = 0, all_lim = fds_lim;
   int i, nfds, tmo_in_millisec;
   bool need_to_dispatch;
   USE_SAFE_ALLOCA;
@@ -59,6 +58,8 @@ xg_select (int fds_lim, fd_set *rfds, fd_set *wfds, fd_set *efds,
   else FD_ZERO (&all_rfds);
   if (wfds) all_wfds = *wfds;
   else FD_ZERO (&all_wfds);
+  if (efds) all_efds = *efds;
+  else FD_ZERO (&all_efds);
 
   n_gfds = g_main_context_query (context, G_PRIORITY_LOW, &tmo_in_millisec,
                                  gfds, gfds_size);
@@ -71,19 +72,22 @@ xg_select (int fds_lim, fd_set *rfds, fd_set *wfds, fd_set *efds,
     }
 
   for (i = 0; i < n_gfds; ++i)
-    {
-      if (gfds[i].events & G_IO_IN)
-        {
-          FD_SET (gfds[i].fd, &all_rfds);
-          if (gfds[i].fd > max_fds) max_fds = gfds[i].fd;
-        }
-      if (gfds[i].events & G_IO_OUT)
-        {
-          FD_SET (gfds[i].fd, &all_wfds);
-          if (gfds[i].fd > max_fds) max_fds = gfds[i].fd;
-          have_wfds = 1;
-        }
-    }
+    if (gfds[i].events & (G_IO_IN | G_IO_OUT | G_IO_PRI))
+      {
+        int fd = gfds[i].fd;
+        for (; all_lim <= fd; all_lim++)
+          {
+            FD_CLR (all_lim, &all_rfds);
+            FD_CLR (all_lim, &all_wfds);
+            FD_CLR (all_lim, &all_efds);
+          }
+        if (gfds[i].events & G_IO_IN)
+          FD_SET (fd, &all_rfds);
+        if (gfds[i].events & G_IO_OUT)
+          FD_SET (fd, &all_wfds);
+        if (gfds[i].events & G_IO_PRI)
+          FD_SET (fd, &all_efds);
+      }
 
   SAFE_FREE ();
 
@@ -95,34 +99,35 @@ xg_select (int fds_lim, fd_set *rfds, fd_set *wfds, fd_set *efds,
         tmop = &tmo;
     }
 
-  fds_lim = max_fds + 1;
-  nfds = pselect (fds_lim, &all_rfds, have_wfds ? &all_wfds : NULL,
-                  efds, tmop, sigmask);
+  nfds = pselect (all_lim, &all_rfds, &all_wfds, &all_efds, tmop, sigmask);
 
   if (nfds < 0)
     retval = nfds;
-  else if (nfds > 0)
+  else
     {
       for (i = 0; i < fds_lim; ++i)
         {
-          if (FD_ISSET (i, &all_rfds))
-            {
-              if (rfds && FD_ISSET (i, rfds)) ++retval;
-              else ++our_fds;
-            }
-          else if (rfds)
-            FD_CLR (i, rfds);
-
-          if (have_wfds && FD_ISSET (i, &all_wfds))
-            {
-              if (wfds && FD_ISSET (i, wfds)) ++retval;
-              else ++our_fds;
-            }
-          else if (wfds)
-            FD_CLR (i, wfds);
-
-          if (efds && FD_ISSET (i, efds))
-            ++retval;
+          if (rfds && FD_ISSET (i, rfds))
+            {
+              if (FD_ISSET (i, &all_rfds))
+                retval++;
+              else
+                FD_CLR (i, rfds);
+            }
+          if (wfds && FD_ISSET (i, wfds))
+            {
+              if (FD_ISSET (i, &all_wfds))
+                retval++;
+              else
+                FD_CLR (i, wfds);
+            }
+          if (efds && FD_ISSET (i, efds))
+            {
+              if (FD_ISSET (i, &all_efds))
+                retval++;
+              else
+                FD_CLR (i, efds);
+            }
         }
     }
 
@@ -142,7 +147,7 @@ xg_select (int fds_lim, fd_set *rfds, fd_set *wfds, fd_set *efds,
     }
 
   /* To not have to recalculate timeout, return like this.  */
-  if ((our_fds > 0 || (nfds == 0 && tmop == &tmo)) && (retval == 0))
+  if (retval == 0 && (0 < nfds || tmop == &tmo))
     {
       retval = -1;
       errno = EINTR;