linux-kernel - Re: [PATCH] mm/mempolicy.c: Fix out of bounds write in mpol_parse

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Date:   Wed, 15 Jan 2020 16:03:15 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Dmitry Vyukov <dvyukov@...gle.com>
Cc:     Vlastimil Babka <vbabka@...e.cz>,
        Dan Carpenter <dan.carpenter@...cle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Lee Schermerhorn <lee.schermerhorn@...com>,
        Linux-MM <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        syzbot <syzbot+e64a13c5369a194d67df@...kaller.appspotmail.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Hugh Dickins <hughd@...gle.com>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
        Al Viro <viro@...iv.linux.org.uk>, yang.shi@...ux.alibaba.com
Subject: Re: [PATCH] mm/mempolicy.c: Fix out of bounds write in
 mpol_parse_str()

On Wed 15-01-20 13:57:47, Dmitry Vyukov wrote:
> On Wed, Jan 15, 2020 at 1:54 PM Vlastimil Babka <vbabka@...e.cz> wrote:
> >
> > On 1/15/20 6:54 AM, Dan Carpenter wrote:
> > > What we are trying to do is change the '=' character to a NUL terminator
> > > and then at the end of the function we restore it back to an '='.  The
> > > problem is there are two error paths where we jump to the end of the
> > > function before we have replaced the '=' with NUL.  We end up putting
> > > the '=' in the wrong place (possibly one element before the start of
> > > the buffer).
> >
> > Bleh.
> >
> > > Reported-by: syzbot+e64a13c5369a194d67df@...kaller.appspotmail.com
> > > Fixes: 095f1fc4ebf3 ("mempolicy: rework shmem mpol parsing and display")
> > > Signed-off-by: Dan Carpenter <dan.carpenter@...cle.com>
> >
> > Acked-by: Vlastimil Babka <vbabka@...e.cz>
> >
> > CC stable perhaps? Can this (tmpfs mount options parsing AFAICS?) become
> > part of unprivileged operation in some scenarios?
> 
> Yes, tmpfs can be mounted by any user inside of a user namespace.

Huh, is there any restriction though? It is certainly not nice to have
an arbitrary memory allocated without a way of reclaiming it and OOM
killer wouldn't help for shmem.
-- 
Michal Hocko
SUSE Labs