linux-kernel - Re: fs/pipe.c null pointer dereference

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Date:	Thu, 15 Oct 2009 20:39:58 -0700
From:	Earl Chew <earl_chew@...lent.com>
To:	unlisted-recipients:; (no To-header on input)
CC:	linux-kernel@...r.kernel.org
Subject: Re: fs/pipe.c null pointer dereference

Earl Chew wrote:
> Is this possible via /proc/pid/fd/* ?

The window for failure is small. It's easiest to reproduce
this problem by stalling pipe_rdwr_open() to open up the
window:

--- pipe.c.orig 2009-10-15 20:33:53.000000000 -0700
+++ pipe.c      2009-10-15 20:17:40.000000000 -0700
@@ -736,2 +736,3 @@
  {
+       msleep(100);
         mutex_lock(&inode->i_mutex);


With the failure window widened, it's easy to reproduce
the failure with:

--------------------------------------------------------------
#!/bin/sh

while : ; do
   { echo y ; sleep 1 ; } | { while read ; do echo z$REPLY; done ; } &
   PID=$!
   OUT=$(ps -efl | grep 'sleep 1' | grep -v grep |
        { read PID REST ; echo $PID; } )
   OUT="${OUT%% *}"
   DELAY=$((RANDOM * 1000 / 32768))
   usleep $((DELAY * 1000 + RANDOM % 1000 ))
   echo n > /proc/$OUT/fd/1
done
--------------------------------------------------------------


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