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From:   Paul Moore <paul@paul-moore.com>
Date:   Fri, 18 Feb 2022 11:22:46 -0500
Message-ID: <CAHC9VhSup7QDQSGxDhbHrpEVNJZ7C0ReDcvuLF=S+1Mb=xRUdQ@mail.gmail.com>
Subject: Re: [PATCH 5/5] selinux: drop unnecessary NULL check
To:     =?UTF-8?Q?Christian_G=C3=B6ttsche?= <cgzones@googlemail.com>
Cc:     selinux@vger.kernel.org,
        Stephen Smalley <stephen.smalley.work@gmail.com>,
        Eric Paris <eparis@parisplace.org>,
        Nathan Chancellor <nathan@kernel.org>,
        Nick Desaulniers <ndesaulniers@google.com>,
        Ondrej Mosnacek <omosnace@redhat.com>,
        Serge Hallyn <serge@hallyn.com>,
        Austin Kim <austin.kim@lge.com>,
        Jiapeng Chong <jiapeng.chong@linux.alibaba.com>,
        Casey Schaufler <casey@schaufler-ca.com>,
        Yang Li <yang.lee@linux.alibaba.com>,
        linux-kernel@vger.kernel.org, llvm@lists.linux.dev
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On Thu, Feb 17, 2022 at 9:22 AM Christian G=C3=B6ttsche
<cgzones@googlemail.com> wrote:
>
> Commit e3489f8974e1 ("selinux: kill selinux_sb_get_mnt_opts()")
> introduced a NULL check on the context after a successful call to
> security_sid_to_context().  This is on the one hand redundant after
> checking for success and on the other hand insufficient on an actual
> NULL pointer, since the context is passed to seq_escape() leading to a
> call of strlen() on it.
>
> Reported by Clang analyzer:
>
>     In file included from security/selinux/hooks.c:28:
>     In file included from ./include/linux/tracehook.h:50:
>     In file included from ./include/linux/memcontrol.h:13:
>     In file included from ./include/linux/cgroup.h:18:
>     ./include/linux/seq_file.h:136:25: warning: Null pointer passed as 1s=
t argument to string length function [unix.cstring.NullArg]
>             seq_escape_mem(m, src, strlen(src), flags, esc);
>                                    ^~~~~~~~~~~

Interesting.  If I'm understanding this correctly, Clang is reporting
on a potential NULL pointer simply because we are checking for a NULL
pointer a few lines earlier, even though @context should not be NULL
if (rc !=3D 0)?

> Signed-off-by: Christian G=C3=B6ttsche <cgzones@googlemail.com>
> ---
>  security/selinux/hooks.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
> index 1e69f88eb326..ac802b99d36c 100644
> --- a/security/selinux/hooks.c
> +++ b/security/selinux/hooks.c
> @@ -1020,7 +1020,7 @@ static int show_sid(struct seq_file *m, u32 sid)
>         rc =3D security_sid_to_context(&selinux_state, sid,
>                                              &context, &len);
>         if (!rc) {
> -               bool has_comma =3D context && strchr(context, ',');
> +               bool has_comma =3D strchr(context, ',');
>
>                 seq_putc(m, '=3D');
>                 if (has_comma)
> --
> 2.35.1

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