From a9664395b06261b0c1189be537d8003974c0e7ed Mon Sep 17 00:00:00 2001
From: Peter Putz <peter@pycom.io>
Date: Wed, 11 Nov 2020 12:21:01 +0100
Subject: [PATCH] pppos: fix in_tail null

happens during quick reconnect of LTE ppp session
---
 src/netif/ppp/pppos.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/src/netif/ppp/pppos.c b/src/netif/ppp/pppos.c
index f8ae8366..88475366 100644
--- a/src/netif/ppp/pppos.c
+++ b/src/netif/ppp/pppos.c
@@ -536,6 +536,12 @@ pppos_input(ppp_pcb *ppp, const void *s, int l)
           /* Note: If you get lots of these, check for UART frame errors or try different baud rate */
           LINK_STATS_INC(link.chkerr);
           pppos_input_drop(pppos);
+        } else if (!pppos->in_tail) {
+          PPPDEBUG(LOG_INFO,
+                   ("pppos_input[%d]: Dropping null in_tail\n",
+                    ppp->netif->num));
+          LINK_STATS_INC(link.drop);
+          pppos_input_drop(pppos);
         /* Otherwise it's a good packet so pass it on. */
         } else {
           struct pbuf *inp;