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From: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
To: David Rientjes <rientjes@google.com>
CC: Kazutomo Yoshii <kazutomo.yoshii@gmail.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        "linux-mm@kvack.org" <linux-mm@kvack.org>
Subject: Re: [PATCH] mm: pagewalk: prevent positive return value of
 walk_page_test() from being passed to callers (Re: [PATCH] mm: fix do_mbind
 return value)
Thread-Topic: [PATCH] mm: pagewalk: prevent positive return value of
 walk_page_test() from being passed to callers (Re: [PATCH] mm: fix do_mbind
 return value)
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Date: Thu, 5 Mar 2015 08:27:29 +0000
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> > From 107fa3fb256bddff40a882c90af717af9863aed7 Mon Sep 17 00:00:00 2001
> > From: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
> > Date: Thu, 5 Mar 2015 16:37:37 +0900
> > Subject: [PATCH] mm: pagewalk: prevent positive return value of
> >  walk_page_test() from being passed to callers
> > 
> > walk_page_test() is purely pagewalk's internal stuff, and its positive return
> > values are not intended to be passed to the callers of pagewalk. However, in
> > the current code if the last vma in the do-while loop in walk_page_range()
> > happens to return a positive value, it leaks outside walk_page_range().
> > So the user visible effect is invalid/unexpected return value (according to
> > the reporter, mbind() causes it.)
> > 
> > This patch fixes it simply by reinitializing the return value after checked.
> > 
> > Another exposed interface, walk_page_vma(), already returns 0 for such cases
> > so no problem.
> > 
> > Fixes: 6f4576e3687b ("mempolicy: apply page table walker on queue_pages_range()")
> 
> This is not a right tag. To be precise, the bug was introduced by commit
> fafaa4264eba ("pagewalk: improve vma handling"), so
> 
>   Fixes fafaa4264eba ("pagewalk: improve vma handling")
> 
> is right.
> 
> Thanks,
> Naoya Horiguchi
> 
> > Reported-by: Kazutomo Yoshii <kazutomo.yoshii@gmail.com>

Ah, I might be a kind of rude, the original idea was posted by Yoshii-san,
and I changed it, so I may as well add his Signed-off-by (additional to
Reported-by) ?