linux-kernel - Re: [PATCH v3] sysctl: expose sysctl_check

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Message-ID: <opxtvf4uk7joyd5wqij5a4uffzwnkfgppxgfkirudm5gtwbdyx@olcdcwt3kjo2>
Date: Mon, 13 Jan 2025 11:01:45 +0100
From: Joel Granados <joel.granados@...nel.org>
To: John Sperbeck <jsperbeck@...gle.com>
Cc: Kees Cook <kees@...nel.org>, Wen Yang <wen.yang@...ux.dev>, 
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH v3] sysctl: expose sysctl_check_table for unit testing
 and use it

On Sun, Jan 12, 2025 at 11:00:01PM -0800, John Sperbeck wrote:
> In commit b5ffbd139688 ("sysctl: move the extra1/2 boundary check
> of u8 to sysctl_check_table_array"), a kunit test was added that
> registers a sysctl table.  If the test is run as a module, then a
> lingering reference to the module is left behind, and a 'sysctl -a'
> leads to a panic.
> 
> This can be reproduced with these kernel config settings:
> 
>     CONFIG_KUNIT=y
>     CONFIG_SYSCTL_KUNIT_TEST=m
> 
> Then run these commands:
> 
>     modprobe sysctl-test
>     rmmod sysctl-test
>     sysctl -a
> 
> The panic varies but generally looks something like this:
> 
>     BUG: unable to handle page fault for address: ffffa4571c0c7db4
>     #PF: supervisor read access in kernel mode
>     #PF: error_code(0x0000) - not-present page
>     PGD 100000067 P4D 100000067 PUD 100351067 PMD 114f5e067 PTE 0
>     Oops: Oops: 0000 [#1] SMP NOPTI
>     ... ... ...
>     RIP: 0010:proc_sys_readdir+0x166/0x2c0
>     ... ... ...
>     Call Trace:
>      <TASK>
>      iterate_dir+0x6e/0x140
>      __se_sys_getdents+0x6e/0x100
>      do_syscall_64+0x70/0x150
>      entry_SYSCALL_64_after_hwframe+0x76/0x7e
> 
> Instead of fully registering a sysctl table, expose the underlying
> checking function and use it in the unit test.
thx for taking the time to change it. I have added it to my backlog and
will get to it at some point. It is not pressing as this touches sysctl
testing, which should not be used in the wild.

I know why you created the V3, but please add a comment on the mail (not
the commit) of what changed in every version.

Best

-- 

Joel Granados