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

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Message-ID: <459D4897.4020408@redhat.com>
Date:	Thu, 04 Jan 2007 12:33:59 -0600
From:	Eric Sandeen <sandeen@...hat.com>
To:	Andrew Morton <akpm@...l.org>
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

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....

> 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);
}

Thanks,
-Eric
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