From 898975ee8b892cadd04322dc884b3bb8d491c8f8 Mon Sep 17 00:00:00 2001
From: Mark Wooding <mdw@distorted.org.uk>
Date: Sat, 22 May 2010 12:40:34 +0100
Subject: [PATCH] server/tun-slip.c, server/tripe-admin.5.in: Handle write
 errors.

The error handling here is a little delicate.  SLIP pipes are marked
nonblocking, so that a slow driver won't hold up the server.  We ignore
EWOULDBLOCK/EAGAIN on the grounds that a dropped packet isn't particularly
disastrous and SLIP is pretty good at resynchronizing.  Other errors
break the tunnel; we issue a warning and stop bothering to write
packets at all until the interface is released and reassigned.  Obviously
dynamic interfaces will be discarded completely; static ones might be
left broken, but at least we'll retry.

Also, add the new warning to the documentation, since write errors weren't
previously something we worried about.
---
 server/tripe-admin.5.in |  3 +++
 server/tun-slip.c       | 34 ++++++++++++++++++++++++++++++++--
 2 files changed, 35 insertions(+), 2 deletions(-)

diff --git a/server/tripe-admin.5.in b/server/tripe-admin.5.in
index e921cfcf..21426747 100644
--- a/server/tripe-admin.5.in
+++ b/server/tripe-admin.5.in
@@ -1436,6 +1436,9 @@ Configuring the Linux TUN/TAP interface failed.
 .BI "TUN " ifname " " tun-name " read-error " ecode " " message
 Reading from the tunnel device failed.
 .SP
+.BI "TUN " ifname " " tun-name " write-error " ecode " " message
+Writing from the tunnel device failed.
+.SP
 .BI "TUN " ifname " slip bad-escape"
 The SLIP driver encountered a escaped byte it wasn't expecting to see.
 The erroneous packet will be ignored.
diff --git a/server/tun-slip.c b/server/tun-slip.c
index 993aca9d..e807662a 100644
--- a/server/tun-slip.c
+++ b/server/tun-slip.c
@@ -52,6 +52,7 @@ struct tunnel {
 #   define ST_BAD 2u			/*   This packet is malformed */
 #   define ST_MASK 3u			/*   Mask for the above bits */
 #   define ST_EOF 4u			/*   File descriptor reported EOF */
+#   define ST_BROKEN 8u			/*   Sending side is broken */
   size_t n;				/* Number of bytes used in buffer */
   octet buf[PKBUFSZ];			/* Buffer for incoming data */
 };
@@ -245,6 +246,29 @@ whine:
   moan("bad slip interface list");
 }
 
+/* --- @t_broken@ --- *
+ *
+ * Arguments:	@tunnel *t@ = pointer to the tunnel
+ *
+ * Returns:	---
+ *
+ * Use:		Marks the tunnel as broken and reports an error.
+ */
+
+static void t_broken(tunnel *t)
+{
+  if (errno == EINTR ||
+#if defined(EWOULDBLOCK) && EWOULDBLOCK != EAGAIN
+      errno == EWOULDBLOCK ||
+#endif
+      errno == EAGAIN)
+    return;
+  a_warn("TUN", "%s", p_ifname(t->p), "slip",
+	 "write-error", "?ERRNO", A_END);
+  T( trace(T_TUNNEL, "tun-slip: marking tunnel broken"); )
+  t->st |= ST_BROKEN;
+}
+
 /* --- @t_create@ --- *
  *
  * Arguments:	@peer *p@ = pointer to peer block
@@ -342,7 +366,8 @@ found:
   sl->f |= F_INUSE;
   sel_initfile(&sel, &t->f, sl->ifd, SEL_READ, t_read, t);
   sel_addfile(&t->f);
-  write(sl->ofd, end, sizeof(end));
+  if (write(sl->ofd, end, sizeof(end)) < 0)
+    t_broken(t);
   *ifn = xstrdup(sl->name);
   dstr_destroy(&d);
   return (t);
@@ -394,6 +419,10 @@ static void t_inject(tunnel *t, buf *b)
     trace_block(T_PACKET, "tun-slip: packet contents", BBASE(b), BLEN(b));
   })
 
+  if (t-> st & ST_BROKEN) {
+    T( trace(T_TUNNEL, "tun-slip: tunnel broken; discarding"); )
+    return;
+  }
   q = buf;
   *q++ = SL_END;
   for (p = BBASE(b), l = BCUR(b); p < l; p++) {
@@ -408,7 +437,8 @@ static void t_inject(tunnel *t, buf *b)
     trace_block(T_PACKET, "tun-slip: SLIP-encapsulated contents",
 		buf, q - buf);
   })
-  write(t->sl->ofd, buf, q - buf);
+  if (write(t->sl->ofd, buf, q - buf) < 0)
+    t_broken(t);
 }
 
 /* --- @t_destroy@ --- *
-- 
2.11.0