linux-kernel - Re: [PATCH 1/1] s390/crash: allow multi-segment iterators

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Date:   Thu, 7 Jul 2022 07:21:55 +0200
From:   Alexander Gordeev <agordeev@...ux.ibm.com>
To:     Alexander Egorenkov <egorenar@...ux.ibm.com>
Cc:     Heiko Carstens <hca@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Matthew Wilcox <willy@...radead.org>,
        Baoquan He <bhe@...hat.com>, Christoph Hellwig <hch@....de>,
        linux-kernel@...r.kernel.org, linux-s390@...r.kernel.org
Subject: Re: [PATCH 1/1] s390/crash: allow multi-segment iterators

On Wed, Jul 06, 2022 at 10:18:15AM +0200, Alexander Egorenkov wrote:
> > +	__iterate_and_advance(iter, csize, base, len, off,
> > +		({ copy_oldmem_user(base, src + off, len) < 0 ? csize : 0; }),
> > +		({ copy_oldmem_kernel(base, src + off, len) < 0 ? csize : 0; })
> 
> Question
> --------
> About return value of STEP in iterate_iovec().
> We return "csize" in case copy_oldmem_*() fails.
> If i'm not mistaken this could lead to an overflow in iterate_iovec():
> 
>   len -= (STEP);
> 
> Because len could be less than csize in case iovec consists of multiple
> segments, one of which is less than csize.
> 
> Better to return len ?

It certainly better. I'll post the fixed version.

> ({ copy_oldmem_user(base, src + off, len) < 0 ? len : 0; })
> 
> > +	)
> >  	return csize;
> >  }
> 
> Another thing is that now we never report any errors in contrast to
> the version before. This is OK ?

I think that is fine. It is consistent with other iterate_and_advance()
uses and actually converted by read_from_oldmem() to -EFAULT in case of
incomplete copy.

Thank you!