linux-kernel - Re: [PATCH v2] tools: Fix use-after-free for realloc(..., 0)

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Message-ID: <20220215221424.hmnei74ar5gtqfy2@treble>
Date:   Tue, 15 Feb 2022 14:14:24 -0800
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:     Kees Cook <keescook@...omium.org>,
        Valdis Klētnieks <valdis.kletnieks@...edu>,
        Arnaldo Carvalho de Melo <acme@...hat.com>,
        Justin Forbes <jmforbes@...uxtx.org>,
        linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH v2] tools: Fix use-after-free for realloc(..., 0)

On Tue, Feb 15, 2022 at 05:42:35PM -0300, Arnaldo Carvalho de Melo wrote:
> Em Mon, Feb 14, 2022 at 12:07:30PM -0800, Josh Poimboeuf escreveu:
> > On Sun, Feb 13, 2022 at 10:24:43AM -0800, Kees Cook wrote:
> > > GCC 12 was correctly reporting a potential use-after-free condition in
> > > the xrealloc helper. Fix the warning by avoiding an implicit "free(ptr)"
> > > when size == 0:
> > > 
> > > In file included from help.c:12:
> > > In function 'xrealloc',
> > >     inlined from 'add_cmdname' at help.c:24:2: subcmd-util.h:56:23: error: pointer may be used after 'realloc' [-Werror=use-after-free]
> > >    56 |                 ret = realloc(ptr, size);
> > >       |                       ^~~~~~~~~~~~~~~~~~
> > > subcmd-util.h:52:21: note: call to 'realloc' here
> > >    52 |         void *ret = realloc(ptr, size);
> > >       |                     ^~~~~~~~~~~~~~~~~~
> > > subcmd-util.h:58:31: error: pointer may be used after 'realloc' [-Werror=use-after-free]
> > >    58 |                         ret = realloc(ptr, 1);
> > >       |                               ^~~~~~~~~~~~~~~
> > > subcmd-util.h:52:21: note: call to 'realloc' here
> > >    52 |         void *ret = realloc(ptr, size);
> > >       |                     ^~~~~~~~~~~~~~~~~~
> > > 
> > > Reported-by: "Valdis Klētnieks" <valdis.kletnieks@...edu>
> > > Fixes: 2f4ce5ec1d44 ("perf tools: Finalize subcmd independence")
> > > Cc: Josh Poimboeuf <jpoimboe@...hat.com>
> > > Signed-off-by: Kees Cook <keescook@...omium.org>
> > > ---
> > > v1: https://lore.kernel.org/lkml/20220212181855.3460176-1-keescook@chromium.org/
> > > v2: simplify logic (josh)
> > 
> > Thanks, running through testing now.
> 
> I assume that testing went ok, may I add a Tested-by: you?

Yes, feel free to add:

Acked-by: Josh Poimboeuf <jpoimboe@...hat.com>

-- 
Josh