linux-kernel - Re: [PATCH 3/3] Coccinelle: pci_free_consistent: Extend whenconstraints for two SmPL ellipses

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Date:   Wed, 15 May 2019 08:10:08 +0200 (CEST)
From:   Julia Lawall <julia.lawall@...6.fr>
To:     wen.yang99@....com.cn
cc:     markus.elfring@....de, Gilles Muller <Gilles.Muller@...6.fr>,
        yamada.masahiro@...ionext.com, michal.lkml@...kovi.net,
        nicolas.palix@...g.fr, cocci@...teme.lip6.fr,
        linux-kernel@...r.kernel.org, wang.yi59@....com.cn,
        cheng.shengyu@....com.cn, ma.jiang@....com.cn
Subject: Re: [PATCH 3/3] Coccinelle: pci_free_consistent: Extend whenconstraints
 for two SmPL ellipses



On Wed, 15 May 2019, wen.yang99@....com.cn wrote:

> Hello,
> > >
> > > A SmPL ellipsis was specified for a search approach so that additional
> > > source code would be tolerated between an assignment to a local variable
> > > and the corresponding null pointer check.
> > >
> > > But such code should be restricted.
> > > * The local variable must not be reassigned there.
> > > * It must also not be forwarded to an other assignment target.
> > >
> > > Take additional casts for these code exclusion specifications into account
> > > together with optional parentheses.
> >
> > I leave this up to the ZTE people.
> > julia
> >
> Thanks.
>
> 1, "id = (T2)(e)" is rare.

Thanks for checking.  I don't really care if it is rare.  There should not
be much cost to this.  On the other hand, I do care about causing false
negatives.  I don't know any more what is the type of id.  Making it
identifier would lead to false negatives as noted below.  It would be
better as something like e2->fld.

julia

> It may be a minor detail that will have no impact in practice.
> We've tested it, and this SmPL may only need to fix the following two false positives:
> ./drivers/net/ethernet/cisco/enic/vnic_dev.c:861:1-7: ERROR: missing pci_free_consistent; pci_alloc_consistent on line 855 and return without freeing on line 861
> ./drivers/message/fusion/mptctl.c:2643:2-8: ERROR: missing pci_free_consistent; pci_alloc_consistent on line 2511 and return without freeing on line 2643
>
> 2,  If you really plan to add the two restrictions above,
> you may need to consider this further than simply adding a "when != id = (T2)(e)" statement.
> I constructed the flollowing code snippet as a test case:
>
> int test()
> {
> 	unsigned char *new_page = NULL;
> 	int ret;
>
> 	new_page = pci_alloc_consistent(dev, 4096, &temp_pci);
> 	if (new_page == NULL)
>     return -1;
> X;
> 	Y;
> 	new_page = Z;
>
> 	return ret;
> }
>
> Using the original SmPL, we can find a bug.
> But with your modified SmPL, we can't find the bug.
>
> --
> Regards,
> Wen
>
> >
> >
> > >
> > > Fixes: f7b167113753e95ae61383e234f8d10142782ace ("scripts: Coccinelle script for pci_free_consistent()")
> > > Signed-off-by: Markus Elfring <elfring@...rs.sourceforge.net>
> > > ---
> > >  scripts/coccinelle/free/pci_free_consistent.cocci | 6 ++++--
> > >  1 file changed, 4 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/scripts/coccinelle/free/pci_free_consistent.cocci b/scripts/coccinelle/free/pci_free_consistent.cocci
> > > index 45bc14ece151..48a36adfa3ce 100644
> > > --- a/scripts/coccinelle/free/pci_free_consistent.cocci
> > > +++ b/scripts/coccinelle/free/pci_free_consistent.cocci
> > > @@ -13,13 +13,15 @@ virtual org
> > >  local idexpression id;
> > >  expression x,y,z,e;
> > >  position p1,p2;
> > > -type T;
> > > +type T,T2,T3,T4;
> > >  @@
> > >
> > >  id = pci_alloc_consistent@p1(x,y,&z)
> > > -... when != e = id
> > > + ... when != id = (T2)(e)
> > > +     when != e = (T3)(id)
> > >  if (id == NULL || ...) { ... return ...; }
> > >  ... when != pci_free_consistent(x,y,id,z)
> > > +    when != id = (T4)(e)
> > >      when != if (id) { ... pci_free_consistent(x,y,id,z) ... }
> > >      when != if (y) { ... pci_free_consistent(x,y,id,z) ... }
> > >      when != e = (T)id
> > > --
> > > 2.21.0
> > >
> > >