Re: [Fwd: [PATCH 1/2] string: Add stracpy and stracpy_pad mechanisms]

Julia Lawall
2019-07-24T11:45:29Z

On Wed, 24 Jul 2019, Joe Perches wrote:

> On Wed, 2019-07-24 at 10:28 +0000, David Laight wrote:
> > From: Joe Perches
> > > Sent: 24 July 2019 05:38
> > > On Tue, 2019-07-23 at 23:27 -0500, Julia Lawall wrote:
> > > > On Tue, 23 Jul 2019, Joe Perches wrote:
> > > > > On Tue, 2019-07-23 at 22:54 -0500, Julia Lawall wrote:
> > > > > > A seantic patch and the resulting output for the case where the third
> > > > > > arugument is a constant is attached. Likewise the resulting output on a
> > > > > > recent linux-next.
> []
> > > > > There is a problem with conversions with assignments
> > > > > of strlcpy() so ideally the cocci script should make sure
> > > > > any return value was not used before conversion.
> > > > >
> > > > > This is not a provably good conversion:
> > > > >
> > > > > drivers/s390/char/sclp_ftp.c
> > > > > @@ -114,8 +114,7 @@ static int sclp_ftp_et7(const struct hmc
> > > > > sccb->evbuf.mdd.ftp.length = ftp->len;
> > > > > sccb->evbuf.mdd.ftp.bufaddr = virt_to_phys(ftp->buf);
> > > > >
> > > > > - len = strlcpy(sccb->evbuf.mdd.ftp.fident, ftp->fname,
> > > > > - HMCDRV_FTP_FIDENT_MAX);
> > > > > + len = stracpy(sccb->evbuf.mdd.ftp.fident, ftp->fname);
> []
> > > Any use of the strlcpy return value should not be converted
> > > because the logic after an assignment or use of the return value
> > > can not be assured to have the same behavior.
> >
> > Most of the code probably expects the length to be that copied
> > (so is broken if the string is truncated).
>
> Fortunately there are relatively few uses of the return
> value of strlcpy so it's not a large problem set.
>
> Slightly unrepresentative counts:
>
> $ git grep -P "^\s+strlcpy\b" | wc -l
> 1681
> $ git grep -P "=\s*strlcpy\b" | wc -l
> 28

OK, it's easy to check for in any case. Thanks.

julia