linux-kernel - Re: [PATCH v2 1/6] sysctl: avoid spurious permanent empty tables

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Message-ID: <20240827084202.6a2efzvosdpbc5ll@joelS2.panther.com>
Date: Tue, 27 Aug 2024 10:42:02 +0200
From: Joel Granados <j.granados@...sung.com>
To: Thomas Weißschuh <linux@...ssschuh.net>
CC: Luis Chamberlain <mcgrof@...nel.org>, Kees Cook <kees@...nel.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 1/6] sysctl: avoid spurious permanent empty tables

On Mon, Aug 05, 2024 at 01:51:55PM +0200, Thomas Weißschuh wrote:
> (trimmed recipients to only sysctl maintainers)
> 
> Hi Joel,
> 
> On 2024-08-05 11:39:35+0000, Thomas Weißschuh wrote:
> > The test if a table is a permanently empty one, inspects the address of
> > the registered ctl_table argument.
> > However as sysctl_mount_point is an empty array and does not occupy and
> > space it can end up sharing an address with another object in memory.
> > If that other object itself is a "struct ctl_table" then registering
> > that table will fail as it's incorrectly recognized as permanently empty.
> > 
> > Avoid this issue by adding a dummy element to the array so that is not
> > empty anymore.
> > Explicitly register the table with zero elements as otherwise the dummy
> > element would be recognized as a sentinel element which would lead to a
> > runtime warning from the sysctl core.
> > 
> > While the issue seems not being encountered at this time, this seems
> > mostly to be due to luck.
> > Also a future change, constifying sysctl_mount_point and root_table, can
> > reliably trigger this issue on clang 18.
> > 
> > Given that empty arrays are non-standard in the first place it seems
> > prudent to avoid them if possible.
> 
> Unfortunately I forgot to include the following trailers in this patch:
> 
> Reported-by: kernel test robot <oliver.sang@...el.com>
> Closes: https://lore.kernel.org/oe-lkp/202408051453.f638857e-lkp@intel.com
> 
> They will be part of v3 if it comes to that, but if you end up applying
> v2, please do also add those trailers.
> 

This is a bugfix and it should be included in the next release. Please send this
commit separately with the Reported-by tag, I'll make sure that this gets pushed
up for 6.11.

I'll add reviewing the rest of the patchset to my "coming back from PTO"
todolist. But since we are so late in the cycle, it might get bumped to the next
release.

Thx

-- 

Joel Granados