From 89e63156991a50263eb6481934ce1c40e4a13036 Mon Sep 17 00:00:00 2001
From: cinap_lenrek <cinap_lenrek@felloff.net>
Date: Thu, 23 Oct 2014 23:59:16 +0200
Subject: [PATCH] lib9p: fix .. walk crash in deleted directory (thanks
 BurnZeZ)

to reproduce:

 % ramfs; cd /tmp
 % mkdir foo; cd foo
 % pwd
 /tmp/foo
 % rm /tmp/foo
 % pwd
 /tmp/foo
 % ls
 % ls /tmp
 % ls ..
 ramfs 202751: suicide: sys: trap: fault read addr=0x0 pc=0x0000e46d
 ls: ..: '..' mount rpc error
---
 sys/src/lib9p/file.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/sys/src/lib9p/file.c b/sys/src/lib9p/file.c
index 1dc324f63..54e09d278 100644
--- a/sys/src/lib9p/file.c
+++ b/sys/src/lib9p/file.c
@@ -254,7 +254,8 @@ walkfile1(File *dir, char *elem)
 	rlock(dir);
 	if(strcmp(elem, "..") == 0){
 		fp = dir->parent;
-		incref(fp);
+		if(fp != nil)
+			incref(fp);
 		runlock(dir);
 		closefile(dir);
 		return fp;