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

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Date:	Wed, 3 Jan 2007 16:26:43 -0800
From:	Andrew Morton <akpm@...l.org>
To:	Eric Sandeen <sandeen@...hat.com>
Cc:	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

On Wed, 03 Jan 2007 17:46:00 -0600
Eric Sandeen <sandeen@...hat.com> wrote:

> Take 2... all in one file.  I suppose I really did know better than 
> to create that new header.   ;-) 
> 
> Better?
> 
> ---
> 
> CVE-2006-5753 is for a case where an inode can be marked bad, switching 
> the ops to bad_inode_ops, which are all connected as:
> 
> static int return_EIO(void)
> {
>         return -EIO;
> }
> 
> #define EIO_ERROR ((void *) (return_EIO))
> 
> static struct inode_operations bad_inode_ops =
> {
>         .create         = bad_inode_create
> ...etc...
> 
> The problem here is that the void cast causes return types to not be 
> promoted, and for ops such as listxattr which expect more than 32 bits of
> return value, the 32-bit -EIO is interpreted as a large positive 64-bit 
> number, i.e. 0x00000000fffffffa instead of 0xfffffffa.
> 
> This goes particularly badly when the return value is taken as a number of
> bytes to copy into, say, a user's buffer for example...
> 
> I originally had coded up the fix by creating a return_EIO_<TYPE> macro
> for each return type, like this:
> 
> static int return_EIO_int(void)
> {
> 	return -EIO;
> }
> #define EIO_ERROR_INT ((void *) (return_EIO_int))
> 
> static struct inode_operations bad_inode_ops =
> {
> 	.create		= EIO_ERROR_INT,
> ...etc...
> 
> but Al felt that it was probably better to create an EIO-returner for each 
> actual op signature.  Since so few ops share a signature, I just went ahead 
> & created an EIO function for each individual file & inode op that returns
> a value.
> 

Al is correct, of course.  But the patch takes bad_inode.o from 280 up to 703
bytes, which is a bit sad for some cosmetic thing which nobody ever looks
at or modifies.

Perhaps you can do

static int return_EIO_int(void)
{
	return -EIO;
}

static int bad_file_release(struct inode * inode, struct file * filp)
	__attribute__((alias("return_EIO_int")));
static int bad_file_fsync(struct inode * inode, struct file * filp)
	__attribute__((alias("return_EIO_int")));

etcetera?
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