linux-kernel - Re: [PATCH v2] mm/mempolicy: do not allow illegal MPOL_F_NUMA_BALANCING

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Date:   Fri, 08 Oct 2021 09:22:54 +0800
From:   "Huang, Ying" <ying.huang@...el.com>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-mm <linux-mm@...ck.org>,
        Eric Dumazet <edumazet@...gle.com>,
        syzbot <syzkaller@...glegroups.com>, Mel Gorman <mgorman@...e.de>
Subject: Re: [PATCH v2] mm/mempolicy: do not allow illegal
 MPOL_F_NUMA_BALANCING | MPOL_LOCAL in mbind()

Hi, Eric,

Eric Dumazet <eric.dumazet@...il.com> writes:

> From: Eric Dumazet <edumazet@...gle.com>
>
> syzbot reported access to unitialized memory in mbind() [1]
>
> Issue came with commit bda420b98505 ("numa balancing: migrate on
> fault among multiple bound nodes")
>
> This commit added a new bit in MPOL_MODE_FLAGS, but only checked
> valid combination (MPOL_F_NUMA_BALANCING can only be used with MPOL_BIND)
> in do_set_mempolicy()
>
> This patch moves the check in sanitize_mpol_flags() so that it
> is also used by mbind()

Good catch!  Thanks!  When MPOL_F_NUMA_BALANCING is introduced, it is
intended to be used with set_memopolicy() syscall only, it is not
allowed to be used with mbind() syscall at least for now.  But I
misunderstood the original code apparently.

So I think it may be better to return EINVAL for mbind() +
MPOL_F_NUMA_BALANCING?

Best Regards,
Huang, Ying