linux-kernel - Re: [PATCH v4 2/6] proc/sysctl: Check for invalid flags bits

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Date:   Mon, 12 Mar 2018 17:02:55 -0400
From:   Waiman Long <longman@...hat.com>
To:     "Luis R. Rodriguez" <mcgrof@...nel.org>
Cc:     Kees Cook <keescook@...omium.org>, linux-kernel@...r.kernel.org,
        linux-fsdevel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Matthew Wilcox <willy@...radead.org>
Subject: Re: [PATCH v4 2/6] proc/sysctl: Check for invalid flags bits

On 03/12/2018 04:59 PM, Luis R. Rodriguez wrote:
> On Mon, Mar 12, 2018 at 04:54:51PM -0400, Waiman Long wrote:
>> On 03/12/2018 04:46 PM, Luis R. Rodriguez wrote:
>>> On Mon, Mar 12, 2018 at 04:15:40PM -0400, Waiman Long wrote:
>>>> Checking code is added to check for invalid flags in the ctl_table
>>>> and return error if an unknown flag is used.
>>> This should be merged with the first patch otherwise there are atomic
>>> points in time on the commit log history where invalid values are allowed
>>> and that makes no sense.
>>>
>>> This can probably be expanded to verify semantics further. Details
>>> below.
>>>> Signed-off-by: Waiman Long <longman@...hat.com>
>>>> ---
>>>>  fs/proc/proc_sysctl.c | 12 ++++++++++++
>>>>  1 file changed, 12 insertions(+)
>>>>
>>>> diff --git a/fs/proc/proc_sysctl.c b/fs/proc/proc_sysctl.c
>>>> index 493c975..67c0c82 100644
>>>> --- a/fs/proc/proc_sysctl.c
>>>> +++ b/fs/proc/proc_sysctl.c
>>>> @@ -1092,6 +1092,16 @@ static int sysctl_check_table_array(const char *path, struct ctl_table *table)
>>>>  	return err;
>>>>  }
>>>>  
>>>> +static int sysctl_check_flags(const char *path, struct ctl_table *table)
>>>> +{
>>>> +	int err = 0;
>>>> +
>>>> +	if (table->flags & ~CTL_TABLE_FLAGS_ALL)
>>>> +		err = sysctl_err(path, table, "invalid flags");
>>> What if a range for the upper limit is set but not the lower limit and
>>> the user goes over the lower limit?
>>>
>>> How about the inverse?
>>>
>>> Do we need both ranges set?
>>>
>>>   Luis
>> This check is just to make sure that no invalid flag bit is set. Range
>> clamping is just one of flag bits, though this is the only one currently
>> supported. In fact, it is allowed that the minimum or maximum can be
>> left unspecified. In this case, no minimum or maximum checking will be
>> done. So I don't see anything related to range checking should be put here.
> What if minimum is greater than maximum?
>
>   Luis

Yes, you are right. That is a valid check. I am going to add that in the
next patch.

Cheers,
Longman