linux-kernel - Re: mainline build failure due to 6c77676645ad ("iov_iter: Fix iter_xarray_get_pages{,

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Message-ID: <CADVatmOJvTj21vrL5cnAVjWx46cB4r_kB+T2ankDj+mKH2-7=w@mail.gmail.com>
Date:   Sun, 12 Jun 2022 00:16:21 +0100
From:   Sudip Mukherjee <sudipm.mukherjee@...il.com>
To:     Al Viro <viro@...iv.linux.org.uk>
Cc:     David Howells <dhowells@...hat.com>,
        Dominique Martinet <asmadeus@...ewreck.org>,
        Mike Marshall <hubcap@...ibond.com>,
        Gao Xiang <xiang@...nel.org>, linux-afs@...ts.infradead.org,
        v9fs-developer@...ts.sourceforge.net, devel@...ts.orangefs.org,
        linux-erofs@...ts.ozlabs.org, linux-cachefs@...hat.com,
        linux-fsdevel@...r.kernel.org,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: mainline build failure due to 6c77676645ad ("iov_iter: Fix iter_xarray_get_pages{,_alloc}()")

On Sat, Jun 11, 2022 at 1:56 PM Al Viro <viro@...iv.linux.org.uk> wrote:
>
> On Sat, Jun 11, 2022 at 12:37:44PM +0000, Al Viro wrote:
> > On Sat, Jun 11, 2022 at 12:12:47PM +0000, Al Viro wrote:
> >
> >
> > > At a guess, should be
> > >     return min((size_t)nr * PAGE_SIZE - offset, maxsize);
> > >
> > > in both places.  I'm more than half-asleep right now; could you verify that it
> > > (as the last lines of both iter_xarray_get_pages() and iter_xarray_get_pages_alloc())
> > > builds correctly?
> >
> > No, I'm misreading it - it's unsigned * unsigned long - unsigned vs. size_t.
> > On arm it ends up with unsigned long vs. unsigned int; functionally it *is*
> > OK (both have the same range there), but it triggers the tests.  Try
> >
> >       return min_t(size_t, nr * PAGE_SIZE - offset, maxsize);
> >
> > there (both places).
>
> The reason we can't overflow on multiplication there, BTW, is that we have
> nr <= count, and count has come from weirdly open-coded
>         DIV_ROUND_UP(size + offset, PAGE_SIZE)
> IMO we'd better make it explicit, so how about the following:

Thanks. Fixed the build for me.


-- 
Regards
Sudip