Re: [PATCH RFC 0/5] ubifs: Prevent memory oob accessing while dumping node

From: Richard Weinberger
Date: Sat Oct 31 2020 - 17:13:31 EST


On Mon, Oct 19, 2020 at 5:13 AM Zhihao Cheng <chengzhihao1@xxxxxxxxxx> wrote:
>
> 在 2020/6/16 15:11, Zhihao Cheng 写道:
> > 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. Length
> > of type A node is greater than type B node.
> >
> > Commit acc5af3efa303d5f3 ("ubifs: Fix out-of-bounds memory access caused
> > 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 allocated
> > 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 memory
> > access caused by abnormal value of node_len") to prepare for patch 3.
> >
> > Patch 3 replaces modified function ubifs_dump_node() in all node dumping
> > 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=208203
> >
> > 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.

--
Thanks,
//richard