[PATCH] selinux: add AF_UNSPEC and INADDR_ANY checks to selinux_socket_bind()

[Stephen Smalley]

On 05/08/2018 01:05 PM, Paul Moore wrote:
> On Tue, May 8, 2018 at 10:05 AM, Alexey Kodanev
> <alexey.kodanev at oracle.com> wrote:
>> Commit d452930fd3b9 ("selinux: Add SCTP support") breaks compatibility
>> with the old programs that can pass sockaddr_in with AF_UNSPEC and
>> INADDR_ANY to bind(). As a result, bind() returns EAFNOSUPPORT error.
>> It was found with LTP/asapi_01 test.
>>
>> Similar to commit 29c486df6a20 ("net: ipv4: relax AF_INET check in
>> bind()"), which relaxed AF_INET check for compatibility, add AF_UNSPEC
>> case to AF_INET and make sure that the address is INADDR_ANY.
>>
>> Also, in the end of selinux_socket_bind(), instead of adding AF_UNSPEC
>> to 'address->sa_family == AF_INET', verify AF_INET6 first.
>>
>> Fixes: d452930fd3b9 ("selinux: Add SCTP support")
>> Signed-off-by: Alexey Kodanev <alexey.kodanev at oracle.com>
>> ---
>>  security/selinux/hooks.c | 12 +++++++++---
>>  1 file changed, 9 insertions(+), 3 deletions(-)
> 
> Thanks for finding and reporting this regression.
> 
> I think I would prefer to avoid having to duplicate the
> AF_UNSPEC/INADDR_ANY checking logic in the SELinux hook, even though
> it is a small bit of code and unlikely to change.  I'm wondering if it
> would be better to check both the socket and sockaddr address family
> in the main if conditional inside selinux_socket_bind(), what do you
> think?  Another option would be to go back to just checking the
> soackaddr address family; we moved away from that for a reason which
> escapes at the moment (code cleanliness?), but perhaps that was a
> mistake.

We've always used the sk->sk_family there; it was only the recent code from Richard that started
using the socket address family.

> 
> diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
> index 4cafe6a19167..a3789b167667 100644
> --- a/security/selinux/hooks.c
> +++ b/security/selinux/hooks.c
> @@ -4577,6 +4577,7 @@ static int selinux_socket_bind(struct socket *sock, struc>
> {
>        struct sock *sk = sock->sk;
>        u16 family;
> +       u16 family_sa;
>        int err;
> 
>        err = sock_has_perm(sk, SOCKET__BIND);
> @@ -4585,7 +4586,9 @@ static int selinux_socket_bind(struct socket *sock, struc>
> 
>        /* If PF_INET or PF_INET6, check name_bind permission for the port. */
>        family = sk->sk_family;
> -       if (family == PF_INET || family == PF_INET6) {
> +       family_sa = address->sa_family;
> +       if ((family == PF_INET || family == PF_INET6) &&
> +           (family_sa == PF_INET || family_sa == PF_INET6)) {

Wouldn't this allow bypassing the name_bind permission check by passing in AF_UNSPEC?

>                char *addrp;
>                struct sk_security_struct *sksec = sk->sk_security;
>                struct common_audit_data ad;
> @@ -4601,7 +4604,7 @@ static int selinux_socket_bind(struct socket *sock, struc>
>                 * need to check address->sa_family as it is possible to have
>                 * sk->sk_family = PF_INET6 with addr->sa_family = AF_INET.
>                 */
> -               switch (address->sa_family) {
> +               switch (family_sa) {
>                case AF_INET:
>                        if (addrlen < sizeof(struct sockaddr_in))
>                                return -EINVAL;
> 
>> diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
>> index 4cafe6a..649a3be 100644
>> --- a/security/selinux/hooks.c
>> +++ b/security/selinux/hooks.c
>> @@ -4602,10 +4602,16 @@ static int selinux_socket_bind(struct socket *sock, struct sockaddr *address, in
>>                  * sk->sk_family = PF_INET6 with addr->sa_family = AF_INET.
>>                  */
>>                 switch (address->sa_family) {
>> +               case AF_UNSPEC:
>>                 case AF_INET:
>>                         if (addrlen < sizeof(struct sockaddr_in))
>>                                 return -EINVAL;
>>                         addr4 = (struct sockaddr_in *)address;
>> +
>> +                       if (address->sa_family == AF_UNSPEC &&
>> +                           addr4->sin_addr.s_addr != htonl(INADDR_ANY))
>> +                               return -EAFNOSUPPORT;
>> +
>>                         snum = ntohs(addr4->sin_port);
>>                         addrp = (char *)&addr4->sin_addr.s_addr;
>>                         break;
>> @@ -4681,10 +4687,10 @@ static int selinux_socket_bind(struct socket *sock, struct sockaddr *address, in
>>                 ad.u.net->sport = htons(snum);
>>                 ad.u.net->family = family;
>>
>> -               if (address->sa_family == AF_INET)
>> -                       ad.u.net->v4info.saddr = addr4->sin_addr.s_addr;
>> -               else
>> +               if (address->sa_family == AF_INET6)
>>                         ad.u.net->v6info.saddr = addr6->sin6_addr;
>> +               else
>> +                       ad.u.net->v4info.saddr = addr4->sin_addr.s_addr;
>>
>>                 err = avc_has_perm(&selinux_state,
>>                                    sksec->sid, sid,
>> --
>> 1.8.3.1
>>
> 

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