Message-ID: <459D6F17.2050208@redhat.com>
Date: Thu, 04 Jan 2007 15:18:15 -0600
From: Eric Sandeen <sandeen@redhat.com>
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To: Andrew Morton <akpm@osdl.org>
CC: Al Viro <viro@ftp.linux.org.uk>, Linus Torvalds <torvalds@osdl.org>,
       Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
       Al Viro <viro@zeniv.linux.org.uk>
Subject: Re: [UPDATED PATCH] fix memory corruption from misinterpreted bad_inode_ops
 return values
References: <459C4038.6020902@redhat.com>	<20070103162643.5c479836.akpm@osdl.org>	<459D3E8E.7000405@redhat.com>	<20070104102659.8c61d510.akpm@osdl.org>	<459D4897.4020408@redhat.com>	<20070104105430.1de994a7.akpm@osdl.org>	<Pine.LNX.4.64.0701041104021.3661@woody.osdl.org>	<20070104191451.GW17561@ftp.linux.org.uk>	<Pine.LNX.4.64.0701041127350.3661@woody.osdl.org>	<20070104202412.GY17561@ftp.linux.org.uk>	<20070104130028.39aa44b8.akpm@osdl.org>	<459D6BD1.7050406@redhat.com> <20070104131008.1d95cb0c.akpm@osdl.org>
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Andrew Morton wrote:
> On Thu, 04 Jan 2007 15:04:17 -0600
> Eric Sandeen <sandeen@redhat.com> wrote:
> 
>> Andrew Morton wrote:
>>> On Thu, 4 Jan 2007 20:24:12 +0000
>>> Al Viro <viro@ftp.linux.org.uk> wrote:
>>>
>>>> So my main issue with fs/bad_inode.c is not even cast per se; it's that
>>>> cast is to void *.
>>> But Eric's latest patch is OK in that regard, isn't it?  It might confuse
>>> parsers (in fixable ways), but it is type-correct and has no casts.  (Well,
>>> it kinda has an link-time cast).
>> Even if it is, I'm starting to wonder if all this tricksiness is really
>> worth it for 400 bytes or so.  :)
>>
> 
> Ah, but it's a learning opportunity!

*grin*

> btw, couldn't we fix this bug with a simple old
> 
> --- a/fs/bad_inode.c~a
> +++ a/fs/bad_inode.c
> @@ -15,7 +15,7 @@
>  #include <linux/smp_lock.h>
>  #include <linux/namei.h>
>  
> -static int return_EIO(void)
> +static long return_EIO(void)
>  {
>  	return -EIO;
>  }
> _
> 
> ?

What about ops that return loff_t (64 bits) on 32-bit arches and stuff
it into 2 registers....

#include <stdio.h>
#include <sys/types.h>
#include <sys/errno.h>

static long return_EIO(void)
{
        return -EIO;
}

#define EIO_ERROR ((void *) (return_EIO))

int main(int argc, char ** argv)
{
        loff_t error;
        loff_t (*fn_ptr) (int);

        fn_ptr = EIO_ERROR;

        error = fn_ptr(0);
        printf("and... error is %lld\n", error);
        return 0;
}

[root]# ./ssize_eio
and... error is 8589934587
[root]# uname -m
i686

I'm still not convinced that this is the best place to be clever :)

-Eric
-
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