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From:   Richard Weinberger <richard.weinberger@gmail.com>
Date:   Sat, 31 Oct 2020 22:13:16 +0100
Message-ID: <CAFLxGvyi1hVLmQ3Q8+nGZT-wgHVjwBewmg4NdEQ=iX5svJsY2Q@mail.gmail.com>
Subject: Re: [PATCH RFC 0/5] ubifs: Prevent memory oob accessing while dumping node
To:     Zhihao Cheng <chengzhihao1@huawei.com>
Cc:     linux-mtd@lists.infradead.org, LKML <linux-kernel@vger.kernel.org>,
        Richard Weinberger <richard@nod.at>, liu.song11@zte.com.cn,
        "zhangyi (F)" <yi.zhang@huawei.com>
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On Mon, Oct 19, 2020 at 5:13 AM Zhihao Cheng <chengzhihao1@huawei.com> wrot=
e:
>
> =E5=9C=A8 2020/6/16 15:11, Zhihao Cheng =E5=86=99=E9=81=93:
> > We use function ubifs_dump_node() to dump bad node caused by some
> > reasons (Such as bit flipping caused by hardware error, writing bypass
> > ubifs or unknown bugs in ubifs). The node content can not be trusted
> > anymore, so we should prevent memory out-of-bounds accessing while
> > dumping node in following situations:
> >
> > 1. bad node_len: Dumping data according to 'ch->len' which may exceed
> >     the size of memory allocated for node.
> > 2. bad node content: Some kinds of node can record additional data, eg.
> >     index node and orphan node, make sure the size of additional data
> >     not beyond the node length.
> > 3. node_type changes: Read data according to type A, but expected type
> >     B, before that, node is allocated according to type B's size. Lengt=
h
> >     of type A node is greater than type B node.
> >
> > Commit acc5af3efa303d5f3 ("ubifs: Fix out-of-bounds memory access cause=
d
> > by abnormal value of node_len") handles situation 1 for data node only,
> > it would be better if we can solve problems in above situations for all
> > kinds of nodes.
> >
> > Patch 1 adds a new parameter 'node_len'(size of memory which is allocat=
ed
> > for the node) in function ubifs_dump_node(), safe dumping length of the
> > node should be: minimum(ch->len, c->ranges[node_type].max_len, node_len=
).
> > Besides, c->ranges[node_type].min_len can not greater than safe dumping
> > length, which may caused by node_type changes(situation 3).
> >
> > Patch 2 reverts commit acc5af3efa303d5f ("ubifs: Fix out-of-bounds memo=
ry
> > access caused by abnormal value of node_len") to prepare for patch 3.
> >
> > Patch 3 replaces modified function ubifs_dump_node() in all node dumpin=
g
> > places except for ubifs_dump_sleb().
> >
> > Patch 4 removes unused function ubifs_dump_sleb(),
> >
> > Patch 5 allows ubifs_dump_node() to dump all branches of the index node=
.
> >
> > Some tests after patchset applied:
> > https://bugzilla.kernel.org/show_bug.cgi?id=3D208203
> >
> > Zhihao Cheng (5):
> >    ubifs: Limit dumping length by size of memory which is allocated for
> >      the node
> >    Revert "ubifs: Fix out-of-bounds memory access caused by abnormal
> >      value of node_len"
> >    ubifs: Pass node length in all node dumping callers
> >    ubifs: ubifs_dump_sleb: Remove unused function
> >    ubifs: ubifs_dump_node: Dump all branches of the index node
> >
> >   fs/ubifs/commit.c   |   4 +-
> >   fs/ubifs/debug.c    | 111 ++++++++++++++++++++++++++-----------------=
-
> >   fs/ubifs/debug.h    |   5 +-
> >   fs/ubifs/file.c     |   2 +-
> >   fs/ubifs/io.c       |  37 +++++----------
> >   fs/ubifs/journal.c  |   3 +-
> >   fs/ubifs/master.c   |   4 +-
> >   fs/ubifs/orphan.c   |   6 ++-
> >   fs/ubifs/recovery.c |   6 +--
> >   fs/ubifs/replay.c   |   4 +-
> >   fs/ubifs/sb.c       |   2 +-
> >   fs/ubifs/scan.c     |   4 +-
> >   fs/ubifs/super.c    |   2 +-
> >   fs/ubifs/tnc.c      |   8 ++--
> >   fs/ubifs/tnc_misc.c |   4 +-
> >   fs/ubifs/ubifs.h    |   4 +-
> >   16 files changed, 108 insertions(+), 98 deletions(-)
> >
> ping, although it is not a serious problem for ubifs, but dumping extra
> memory by formating specified ubifs img may cause security problem.

Thanks for reminding me, yes this needs fixing.
I'll give it a try and then apply it for next.

--=20
Thanks,
//richard