Re: [PATCH 1/6] scripts/coccinelle: add error-use-after-free.cocci

[Vladimir Sementsov-Ogievskiy]

31.03.2020 12:00, Markus Armbruster wrote:
> Vladimir Sementsov-Ogievskiy <address@hidden> writes:
>
> > Add script to find and fix trivial use-after-free of Error objects.
> > How to use:
> > spatch --sp-file scripts/coccinelle/auto-propagated-errp.cocci \
> >   --macro-file scripts/cocci-macro-file.h --in-place \
> >   --no-show-diff ( FILES... | --use-gitgrep . )
>
> Pasto: you mean scripts/coccinelle/error-use-after-free.cocci.
>
> --use-gitgrep is just one of several methods.  Any particular reason for
> recommending it over the others?

:)

In my occasional coccinelle learning, every new bit of information wanders me, and I 
think "wow! it's tricky/weird/cool (underline whatever applicable), I should note it 
somewhere".

So, no particular reasons. It's just good thing too use.

> > Signed-off-by: Vladimir Sementsov-Ogievskiy <address@hidden>
> > ---
> >   scripts/coccinelle/error-use-after-free.cocci | 52 +++++++++++++++++++
> >   MAINTAINERS                                   |  1 +
> >   2 files changed, 53 insertions(+)
> >   create mode 100644 scripts/coccinelle/error-use-after-free.cocci
> >
> > diff --git a/scripts/coccinelle/error-use-after-free.cocci 
> > b/scripts/coccinelle/error-use-after-free.cocci
> > new file mode 100644
> > index 0000000000..7cfa42355b
> > --- /dev/null
> > +++ b/scripts/coccinelle/error-use-after-free.cocci
> > @@ -0,0 +1,52 @@
> > +// Find and fix trivial use-after-free of Error objects
> > +//
> > +// Copyright (c) 2020 Virtuozzo International GmbH.
> > +//
> > +// This program is free software; you can redistribute it and/or
> > +// modify it under the terms of the GNU General Public License as
> > +// published by the Free Software Foundation; either version 2 of the
> > +// License, or (at your option) any later version.
> > +//
> > +// This program is distributed in the hope that it will be useful,
> > +// but WITHOUT ANY WARRANTY; without even the implied warranty of
> > +// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> > +// GNU General Public License for more details.
> > +//
> > +// You should have received a copy of the GNU General Public License
> > +// along with this program.  If not, see
> > +// <http://www.gnu.org/licenses/>.
> > +//
> > +// How to use:
> > +// spatch --sp-file scripts/coccinelle/auto-propagated-errp.cocci \
> > +//  --macro-file scripts/cocci-macro-file.h --in-place \
> > +//  --no-show-diff ( FILES... | --use-gitgrep . )
>
> Same pasto.
>
> I doubt including basic spatch instructions with every script is a good
> idea.  Better explain it in one place, with proper maintenance.
> scripts/coccinelle/README?  We could be a bit more verbose there,
> e.g. to clarify required vs. suggested options.

Agree, good idea.

> > +
> > +@ exists@
> > +identifier fn, fn2;
> > +expression err;
> > +@@
> > +
> > + fn(...)
> > + {
> > +     <...
> > +(
> > +     error_free(err);
> > ++    err = NULL;
> > +|
> > +     error_report_err(err);
> > ++    err = NULL;
> > +|
> > +     error_reportf_err(err, ...);
> > ++    err = NULL;
> > +|
> > +     warn_report_err(err);
> > ++    err = NULL;
> > +|
> > +     warn_reportf_err(err, ...);
> > ++    err = NULL;
> > +)
> > +     ... when != err = NULL
> > +         when != exit(...)
> > +     fn2(..., err, ...)
> > +     ...>
> > + }
>
> This inserts err = NULL after error_free() if there is a path to a
> certain kind of use of @err without such an assignment.
>
> The "when != exit()" part excludes certain "phony" paths.  It's not a
> tight check; there are other ways to unconditionally terminate the
> process or jump elsewhere behind Coccinelle's back.  Not a problem, the
> script is meant to have its output reviewed manually.
>
> Should we mention the need to review the script's output?

I think it's default thing to do.

> > diff --git a/MAINTAINERS b/MAINTAINERS
> > index b5c86ec494..ba97cc43fc 100644
> > --- a/MAINTAINERS
> > +++ b/MAINTAINERS
> > @@ -2037,6 +2037,7 @@ F: include/qemu/error-report.h
> >   F: qapi/error.json
> >   F: util/error.c
> >   F: util/qemu-error.c
> > +F: scripts/coccinelle/*err*.cocci
>
> Silently captures existing scripts in addition to this new one.
> Tolerable.  The globbing looks rather brittle, though.

hmm, may be better to rename them all to "error-*.cocci"

> >   
> >   GDB stub
> >   M: Alex Bennée <address@hidden>


--
Best regards,
Vladimir