linux-hardening - Re: [PATCH] stackleak: don't modify ctl

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Date: Fri, 3 May 2024 20:24:24 +0200 (GMT+02:00)
From: linux@...ssschuh.net
To: Kees Cook <keescook@...omium.org>
Cc: Thomas Weißschuh <linux@...ssschuh.net>,
	Alexander Popov <alex.popov@...ux.com>,
	linux-hardening@...r.kernel.org, linux-kernel@...r.kernel.org,
	stable@...r.kernel.org, Luis Chamberlain <mcgrof@...nel.org>,
	Joel Granados <j.granados@...sung.com>
Subject: Re: [PATCH] stackleak: don't modify ctl_table argument

May 3, 2024 19:55:37 Kees Cook <keescook@...omium.org>:

> On Fri, May 03, 2024 at 03:44:09PM +0200, Thomas Weißschuh wrote:
>> Sysctl handlers are not supposed to modify the ctl_table passed to them.
>> Adapt the logic to work with a temporary
>> variable, similar to how it is done in other parts of the kernel.
>>
>> This is also a prerequisite to enforce the immutability of the argument
>> through the callbacks prototy.
>>
>> Fixes: 964c9dff0091 ("stackleak: Allow runtime disabling of kernel stack erasing")
>> Cc: stable@...r.kernel.org
>
> I realize I've already Acked, but does this actually need to be CCed
> to stable?

You acked it without the Cc stable.
I shouldn't have kept your Ack, sorry.

Feel free to drop the Cc, it shouldn't be critical.
I suspect the bots will pick it up anyways.

>> Acked-by: Kees Cook <keescook@...omium.org>
>> Reviewed-by: Luis Chamberlain <mcgrof@...nel.org>
>> Signed-off-by: Thomas Weißschuh <linux@...ssschuh.net>
>> ---
>> This was split out of my sysctl-const-handler series [0].
>>
>> As that series will take some more time, submit the patch on its own,
>> as it is a generic bugfix that is valuable on its own.
>> And I can get it out of my books.
>>
>> Changelog in contrast to the patch in the series:
>> * Reword commit message to remove strong relation to the constification
>> * Cc stable
>>
>> [0] https://lore.kernel.org/lkml/20240423-sysctl-const-handler-v3-0-e0beccb836e2@weissschuh.net/
>>
>> Cc: Joel Granados <j.granados@...sung.com>
>> ---
>> kernel/stackleak.c | 7 ++++---
>> 1 file changed, 4 insertions(+), 3 deletions(-)
>>
>> diff --git a/kernel/stackleak.c b/kernel/stackleak.c
>> index 34c9d81eea94..b292e5ca0b7d 100644
>> --- a/kernel/stackleak.c
>> +++ b/kernel/stackleak.c
>> @@ -27,10 +27,11 @@ static int stack_erasing_sysctl(struct ctl_table *table, int write,
>>     int ret = 0;
>>     int state = !static_branch_unlikely(&stack_erasing_bypass);
>>     int prev_state = state;
>> +   struct ctl_table tmp = *table;
>>
>> -   table->data = &state;
>> -   table->maxlen = sizeof(int);
>> -   ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
>> +   tmp.data = &state;
>> +   tmp.maxlen = sizeof(int);
>> +   ret = proc_dointvec_minmax(&tmp, write, buffer, lenp, ppos);
>>     state = !!state;
>>     if (ret || !write || state == prev_state)
>>         return ret;
>
> I can pick this up; thanks!

Thanks!