linux-kernel - Re: [PATCH] filp->f_pos not correctly updated in proc_task

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Message-ID: <20090317103744.GA2399@x200.localdomain>
Date:	Tue, 17 Mar 2009 13:37:44 +0300
From:	Alexey Dobriyan <adobriyan@...il.com>
To:	Al Viro <viro@...IV.linux.org.uk>
Cc:	Zhang Le <r0bertz@...too.org>, linux-kernel@...r.kernel.org,
	torvalds@...l.org, alan@...hat.com
Subject: Re: [PATCH] filp->f_pos not correctly updated in proc_task_readdir

On Mon, Mar 16, 2009 at 08:34:57AM +0000, Al Viro wrote:
> On Mon, Mar 16, 2009 at 02:44:31PM +0800, Zhang Le wrote:
> > filp->f_pos only get updated at the end of the function. Thus d_off of those
> > dirents who are in the middle will be 0, and this will cause a problem in
> > glibc's readdir implementation, specifically endless loop. Because when overflow
> > occurs, f_pos will be set to next dirent to read, however it will be 0, unless
> > the next one is the last one. So it will start over again and again.
> 
> Eh...  Here's what's really going on:
> 
> proc_..._fill_cache() API is rather kludgy and far too convoluted.  In
> particular, it calls filldir() and passes file->f_pos to it, expecting
> the caller to update file->f_pos between the calls.  proc_task_readdir()
> uses that sucker, but doesn't update ->f_pos until the very end.  As
> the result, d_off of direntries produced by it gets screwed.
> Broken-by: commit 61a28784028e6d55755e4d0f39bee8d9bf2ee8d9
> Author: Eric W. Biederman <ebiederm@...ssion.com>
> Date:   Mon Oct 2 02:18:49 2006 -0700
> 
>     [PATCH] proc: Remove the hard coded inode numbers
> 
> Patch is fine, but I'd rather rip the layers of ..._fill_cache() abstractions
> out and see what falls out.  Anyway, for -rc your variant is definitely the
> way to go.

Except this bit:

fs/built-in.o: In function `proc_task_readdir':
compr_zlib.c:(.text+0x434b8): undefined reference to `__cmpdi2'
compr_zlib.c:(.text+0x434d4): undefined reference to `__cmpdi2'
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