Re: [PATCH] selinux: avoid uninitialized variable warning

From: Paul Moore <paul@paul-moore.com>
To: Arnd Bergmann <arnd@arndb.de>
Cc: Stephen Smalley <sds@tycho.nsa.gov>,
	Eric Paris <eparis@parisplace.org>,
	clang-built-linux@googlegroups.com,
	Nick Desaulniers <ndesaulniers@google.com>,
	Nathan Chancellor <natechancellor@gmail.com>,
	selinux@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] selinux: avoid uninitialized variable warning
Date: Fri, 22 Mar 2019 16:15:09 -0400	[thread overview]
Message-ID: <CAHC9VhQuSQr7+y1z3SmY=3s608zYo3JXhF3m_jUWXAo8i8swgw@mail.gmail.com> (raw)
In-Reply-To: <20190322141414.496017-1-arnd@arndb.de>

On Fri, Mar 22, 2019 at 10:14 AM Arnd Bergmann <arnd@arndb.de> wrote:
> clang correctly points out a code path that would lead
> to an uninitialized variable use:
>
> security/selinux/netlabel.c:310:6: error: variable 'addr' is used uninitialized whenever 'if' condition is false
>       [-Werror,-Wsometimes-uninitialized]
>         if (ip_hdr(skb)->version == 4) {
>             ^~~~~~~~~~~~~~~~~~~~~~~~~
> security/selinux/netlabel.c:322:40: note: uninitialized use occurs here
>         rc = netlbl_conn_setattr(ep->base.sk, addr, &secattr);
>                                               ^~~~
> security/selinux/netlabel.c:310:2: note: remove the 'if' if its condition is always true
>         if (ip_hdr(skb)->version == 4) {
>         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> security/selinux/netlabel.c:291:23: note: initialize the variable 'addr' to silence this warning
>         struct sockaddr *addr;
>                              ^
>                               = NULL
> 1 error generated.
>
> This is probably harmless since we should not see ipv6 packets
> of CONFIG_IPV6 is disabled, but it's better to rearrange the code
> so this cannot happen.
>
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> ---
>  security/selinux/netlabel.c | 6 ++----
>  1 file changed, 2 insertions(+), 4 deletions(-)

Hi Arnd,

Thanks for pointing this out and providing a fix.  I think you're
right in that the should be pretty harmless, but I also agree that we
should fix it; some thoughts on the patch below ...

> diff --git a/security/selinux/netlabel.c b/security/selinux/netlabel.c
> index 186e727b737b..d0e549d4f486 100644
> --- a/security/selinux/netlabel.c
> +++ b/security/selinux/netlabel.c
> @@ -288,7 +288,6 @@ int selinux_netlbl_sctp_assoc_request(struct sctp_endpoint *ep,
>         int rc;
>         struct netlbl_lsm_secattr secattr;
>         struct sk_security_struct *sksec = ep->base.sk->sk_security;
> -       struct sockaddr *addr;
>         struct sockaddr_in addr4;
>  #if IS_ENABLED(CONFIG_IPV6)
>         struct sockaddr_in6 addr6;
> @@ -310,16 +309,15 @@ int selinux_netlbl_sctp_assoc_request(struct sctp_endpoint *ep,
>         if (ip_hdr(skb)->version == 4) {
>                 addr4.sin_family = AF_INET;
>                 addr4.sin_addr.s_addr = ip_hdr(skb)->saddr;
> -               addr = (struct sockaddr *)&addr4;
> +               rc = netlbl_conn_setattr(ep->base.sk, (void*)&addr4, &secattr);
>  #if IS_ENABLED(CONFIG_IPV6)
>         } else {
>                 addr6.sin6_family = AF_INET6;
>                 addr6.sin6_addr = ipv6_hdr(skb)->saddr;
> -               addr = (struct sockaddr *)&addr6;
> +               rc = netlbl_conn_setattr(ep->base.sk, (void*)&addr6, &secattr);
>  #endif

While we are hardening the code a bit, I'm thinking we should probably
refactor this if-else a bit, some pseudo code for example:

    if (ip_hdr == 4) {
      rc = netlbl_conn_setattr();
  #if CONFIG_IPV6
    } else if (ip_hdr == 6) {
      rc = netlbl_conn_setattr();
  #endif
    } else {
      rc = -EAFNOSUPPORT;
    }

Thoughts?

>         }
>
> -       rc = netlbl_conn_setattr(ep->base.sk, addr, &secattr);
>         if (rc == 0)
>                 sksec->nlbl_state = NLBL_LABELED;
>
> --
> 2.20.0
>

-- 
paul moore
www.paul-moore.com