Re: [PATCH v2] cifs: small underflow in cnvrtDosUnixTm()

walter harms
2017-04-28T14:57:37Z

Am 28.04.2017 16:41, schrieb Dan Carpenter:
> On Fri, Apr 28, 2017 at 04:40:04PM +0200, walter harms wrote:
>>
>>
>> Am 28.04.2017 14:51, schrieb Dan Carpenter:
>>> January is month 1. There is no zero-th month. If someone passes a
>>> zero month then it means we read from one space before the start of the
>>> total_days_of_prev_months[] array.
>>>
>>> We may as well also be strict about days as well.
>>>
>>> Fixes: 1bd5bbcb6531 ("[CIFS] Legacy time handling for Win9x and OS/2 part 1")
>>> Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
>>> ---
>>> v2: Be strict about days as well. My first patch was less intrusive
>>> because it only prevented the out of bounds access. I have no idea how
>>> common it is to pass in an illegal day but, hopefully, not very common.
>>>
>>> diff --git a/fs/cifs/netmisc.c b/fs/cifs/netmisc.c
>>> index abae6dd2c6b9..4b2726ee4fad 100644
>>> --- a/fs/cifs/netmisc.c
>>> +++ b/fs/cifs/netmisc.c
>>> @@ -980,10 +980,10 @@ struct timespec cnvrtDosUnixTm(__le16 le_date, __le16 le_time, int offset)
>>> cifs_dbg(VFS, "illegal hours %d\n", st->Hours);
>>> days = sd->Day;
>>> month = sd->Month;
>>> - if ((days > 31) || (month > 12)) {
>>> + if (days < 1 || days > 31 || month < 1 || month > 12) {
>>> cifs_dbg(VFS, "illegal date, month %d day: %d\n", month, days);
>>> - if (month > 12)
>>> - month = 12;
>>> + days = (days < 1) ? 1 : ((days <= 31) ? days : 31);
>>> + month = (month < 1) ? 1 : ((month <= 12) ? month : 12);
>>> }
>>> month -= 1;
>>> days += total_days_of_prev_months[month];
>>
>> The mixing in now a bit unfortunate ... why not simply
>>
>> if (days < 1 || days > 31 || month < 1 || month > 12)
>> cifs_dbg(VFS, "illegal date, month %d day: %d\n", month, days);
>>
>> month = (month < 1) ? 1 : ((month <= 12) ? month : 12);
>> days = (days < 1) ? 1 : ((days <= 31) ? days : 31);
>>
>
> I prefer my version because I feel like it more closely expresses what
> I want to say.
>

(Actually it is your code just without the braces.)
what is about differentiating between day and month ?

if (days < 1 || days > 31) {
cifs_dbg(VFS, "illegal day: %d\n", days);
days = (days < 1) ? 1 : 31 ;
}

if ( month < 1 || month > 12) {
cifs_dbg(VFS, "illegal month %d\n", month);
month = (month < 1) ? 1 : 12 ;
}

this way you have a obvious error handling for day and month.

I still like my first version even when day/month are recalculated every
time the flow is very linear only the error message is a deviation.
(Given that ?: makes it not easy to digest)

re,
wh