Re: [PATCH 6.6 00/28] fix CVE-2024-46701

[Chuck Lever <chuck.lever@oracle.com>]

On Thu, Nov 07, 2024 at 08:57:23AM +0800, Yu Kuai wrote:
> Hi,
> 
> 在 2024/11/06 23:19, Chuck Lever III 写道:
> > 
> > 
> > > On Nov 6, 2024, at 1:16 AM, Greg KH <gregkh@linuxfoundation.org> wrote:
> > > 
> > > On Thu, Oct 24, 2024 at 09:19:41PM +0800, Yu Kuai wrote:
> > > > From: Yu Kuai <yukuai3@huawei.com>
> > > > 
> > > > Fix patch is patch 27, relied patches are from:
> > 
> > I assume patch 27 is:
> > 
> > libfs: fix infinite directory reads for offset dir
> > 
> > https://lore.kernel.org/stable/20241024132225.2271667-12-yukuai1@huaweicloud.com/
> > 
> > I don't think the Maple tree patches are a hard
> > requirement for this fix. And note that libfs did
> > not use Maple tree originally because I was told
> > at that time that Maple tree was not yet mature.
> > 
> > So, a better approach might be to fit the fix
> > onto linux-6.6.y while sticking with xarray.
> 
> The painful part is that using xarray is not acceptable, the offet
> is just 32 bit and if it overflows, readdir will read nothing. That's
> why maple_tree has to be used.

A 32-bit range should be entirely adequate for this usage.

 - The offset allocator wraps when it reaches the maximum, it
   doesn't overflow unless there are actually billions of extant
   entries in the directory, which IMO is not likely.

 - The offset values are dense, so the directory can use all 2- or
   4- billion in the 32-bit integer range before wrapping.

 - No-one complained about this limitation when offset_readdir() was
   first merged. The xarray was replaced for performance reasons,
   not because of the 32-bit range limit.

It is always possible that I have misunderstood your concern!


> Thanks,
> Kuai
> 
> > 
> > This is the first I've heard of this CVE. It
> > would help if the patch authors got some
> > notification when these are filed.
> > 
> > 
> > > > - patches from set [1] to add helpers to maple_tree, the last patch to
> > > > improve fork() performance is not backported;
> > > 
> > > So things slowed down?
> > > 
> > > > - patches from set [2] to change maple_tree, and follow up fixes;
> > > > - patches from set [3] to convert offset_ctx from xarray to maple_tree;
> > > > 
> > > > Please notice that I'm not an expert in this area, and I'm afraid to
> > > > make manual changes. That's why patch 16 revert the commit that is
> > > > different from mainline and will cause conflict backporting new patches.
> > > > patch 28 pick the original mainline patch again.
> > > > 
> > > > (And this is what we did to fix the CVE in downstream kernels).
> > > > 
> > > > [1] https://lore.kernel.org/all/20231027033845.90608-1-zhangpeng.00@bytedance.com/
> > > > [2] https://lore.kernel.org/all/20231101171629.3612299-2-Liam.Howlett@oracle.com/T/
> > > > [3] https://lore.kernel.org/all/170820083431.6328.16233178852085891453.stgit@91.116.238.104.host.secureserver.net/
> > > 
> > > This series looks rough.  I want to have the maintainers of these
> > > files/subsystems to ack this before being able to take them.
> > > 
> > > thanks,
> > > 
> > > greg k-h
> > 
> > --
> > Chuck Lever
> > 
> > 
> 

-- 
Chuck Lever