linux-kernel - Re: [PATCH 5/5] selinux: drop unnecessary NULL check

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Message-ID: <CAHC9VhSup7QDQSGxDhbHrpEVNJZ7C0ReDcvuLF=S+1Mb=xRUdQ@mail.gmail.com>
Date:   Fri, 18 Feb 2022 11:22:46 -0500
From:   Paul Moore <paul@...l-moore.com>
To:     Christian Göttsche <cgzones@...glemail.com>
Cc:     selinux@...r.kernel.org,
        Stephen Smalley <stephen.smalley.work@...il.com>,
        Eric Paris <eparis@...isplace.org>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Ondrej Mosnacek <omosnace@...hat.com>,
        Serge Hallyn <serge@...lyn.com>,
        Austin Kim <austin.kim@....com>,
        Jiapeng Chong <jiapeng.chong@...ux.alibaba.com>,
        Casey Schaufler <casey@...aufler-ca.com>,
        Yang Li <yang.lee@...ux.alibaba.com>,
        linux-kernel@...r.kernel.org, llvm@...ts.linux.dev
Subject: Re: [PATCH 5/5] selinux: drop unnecessary NULL check

On Thu, Feb 17, 2022 at 9:22 AM Christian Göttsche
<cgzones@...glemail.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 1st 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 != 0)?

> Signed-off-by: Christian Göttsche <cgzones@...glemail.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 = security_sid_to_context(&selinux_state, sid,
>                                              &context, &len);
>         if (!rc) {
> -               bool has_comma = context && strchr(context, ',');
> +               bool has_comma = strchr(context, ',');
>
>                 seq_putc(m, '=');
>                 if (has_comma)
> --
> 2.35.1

-- 
paul-moore.com