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

Dan Carpenter
2017-04-28T14:41:29Z

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.

regards,
dan carpenter