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

From: Vladimir Sementsov-Ogievskiy
Subject: Re: [PATCH 1/6] scripts/coccinelle: add error-use-after-free.cocci
Date: Tue, 31 Mar 2020 12:12:22 +0300
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.2.1

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 

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 
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
+// 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.

index b5c86ec494..ba97cc43fc 100644
@@ -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,

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