linux-kernel - Re: [PATCH] apparmor: fix error check

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Date:   Mon, 21 Dec 2020 11:22:11 -0800
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Tom Rix <trix@...hat.com>
Cc:     john.johansen@...onical.com, James Morris <jmorris@...ei.org>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        Nathan Chancellor <natechancellor@...il.com>,
        linux-security-module@...r.kernel.org,
        LKML <linux-kernel@...r.kernel.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>
Subject: Re: [PATCH] apparmor: fix error check

On Sun, Oct 4, 2020 at 7:24 AM <trix@...hat.com> wrote:
>
> From: Tom Rix <trix@...hat.com>
>
> clang static analysis reports this representative problem:
>
> label.c:1463:16: warning: Assigned value is garbage or undefined
>         label->hname = name;
>                      ^ ~~~~

Right, so if aa_label_acntsxprint() fails, it won't assign to its
first param. In the caller, this means assigning uninitialized memory
(UB) when aa_label_acntsxprint() returns -ENOMEM for example.  Thanks
for the patch.

Reviewed-by: Nick Desaulniers <ndesaulniers@...gle.com>

>
> In aa_update_label_name(), this the problem block of code
>
>         if (aa_label_acntsxprint(&name, ...) == -1)
>                 return res;
>
> On failure, aa_label_acntsxprint() has a more complicated return
> that just -1.  So check for a negative return.
>
> It was also noted that the aa_label_acntsxprint() main comment refers
> to a nonexistent parameter, so clean up the comment.
>
> Fixes: f1bd904175e8 ("apparmor: add the base fns() for domain labels")
> Signed-off-by: Tom Rix <trix@...hat.com>
> ---
>  security/apparmor/label.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/security/apparmor/label.c b/security/apparmor/label.c
> index e68bcedca976..6222fdfebe4e 100644
> --- a/security/apparmor/label.c
> +++ b/security/apparmor/label.c
> @@ -1454,7 +1454,7 @@ bool aa_update_label_name(struct aa_ns *ns, struct aa_label *label, gfp_t gfp)
>         if (label->hname || labels_ns(label) != ns)
>                 return res;
>
> -       if (aa_label_acntsxprint(&name, ns, label, FLAGS_NONE, gfp) == -1)
> +       if (aa_label_acntsxprint(&name, ns, label, FLAGS_NONE, gfp) < 0)
>                 return res;
>
>         ls = labels_set(label);
> @@ -1704,7 +1704,7 @@ int aa_label_asxprint(char **strp, struct aa_ns *ns, struct aa_label *label,
>
>  /**
>   * aa_label_acntsxprint - allocate a __counted string buffer and print label
> - * @strp: buffer to write to. (MAY BE NULL if @size == 0)
> + * @strp: buffer to write to.
>   * @ns: namespace profile is being viewed from
>   * @label: label to view (NOT NULL)
>   * @flags: flags controlling what label info is printed
> --
> 2.18.1
>
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-- 
Thanks,
~Nick Desaulniers