linux-kernel - Re: [UPDATED PATCH] fix memory corruption from misinterpreted bad_inode

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Date:	Thu, 04 Jan 2007 15:18:15 -0600
From:	Eric Sandeen <sandeen@...hat.com>
To:	Andrew Morton <akpm@...l.org>
CC:	Al Viro <viro@....linux.org.uk>,
	Linus Torvalds <torvalds@...l.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Al Viro <viro@...iv.linux.org.uk>
Subject: Re: [UPDATED PATCH] fix memory corruption from misinterpreted bad_inode_ops
 return values

Andrew Morton wrote:
> On Thu, 04 Jan 2007 15:04:17 -0600
> Eric Sandeen <sandeen@...hat.com> wrote:
> 
>> Andrew Morton wrote:
>>> On Thu, 4 Jan 2007 20:24:12 +0000
>>> Al Viro <viro@....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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