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

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Date:	Thu, 4 Jan 2007 10:54:30 -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>,
	Linus Torvalds <torvalds@...l.org>
Subject: Re: [UPDATED PATCH] fix memory corruption from misinterpreted
 bad_inode_ops return values

On Thu, 04 Jan 2007 12:33:59 -0600
Eric Sandeen <sandeen@...hat.com> wrote:

> Andrew Morton wrote:
> > On Thu, 04 Jan 2007 11:51:10 -0600
> > Eric Sandeen <sandeen@...hat.com> wrote:
> 
> >> Also - is it ok to alias a function with one signature to a function with
> >> another signature?
> > 
> > Ordinarily I'd say no wucking fay, but that's effectively what we've been
> > doing in there for ages, and it seems to work.
> 
> Hmm that gives me a lot of confidence ;-)  I'd hate to carry along bad
> assumptions while we try to make this all kosher... but I'm willing to
> defer to popular opinion on this one....

yeah, I'm a bit wobbly about it.  Linus, what do you think?

> > I'd be a bit worried if any of these functions were returning pointers,
> > because one could certainly conceive of an arch+compiler combo which
> > returns pointers in a different register from integers (680x0?) but that's
> > not happening here.
> 
> Well, one is...
> 
> static long * return_EIO_ptr(void)
> {
>         return ERR_PTR(-EIO);
> }
> ...
> static struct dentry *bad_inode_lookup(struct inode * dir,
>                         struct dentry *dentry, struct nameidata *nd)
>         __attribute__((alias("return_EIO_ptr")));
> 
> Maybe it'd be better to lose the alias in this case then?  and go back
> to this:
> 
> static struct dentry *bad_inode_lookup(struct inode * dir,
>                         struct dentry *dentry, struct nameidata *nd)
> {
>         return ERR_PTR(-EIO);
> }

A bit saner, but again, the old code used the same function for *everything*
and apart from the 32/64-bit thing, it worked.

Half a kb isn't much of course, but we've done lots of changes for a lot
less...


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