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Message-ID: <CAHC9VhTNS-sEL2Az4hs1nmz7naqoyhiohzhPTrqp_M=_Ys1N6A@mail.gmail.com>
Date: Wed, 9 May 2018 11:01:09 -0400
From: Paul Moore <paul@...l-moore.com>
To: Stephen Smalley <sds@...ho.nsa.gov>
Cc: Alexey Kodanev <alexey.kodanev@...cle.com>,
Richard Haines <richard_c_haines@...nternet.com>,
selinux@...ho.nsa.gov, Eric Paris <eparis@...isplace.org>,
linux-security-module@...r.kernel.org,
netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH] selinux: add AF_UNSPEC and INADDR_ANY checks to selinux_socket_bind()
On Wed, May 9, 2018 at 8:37 AM, Stephen Smalley <sds@...ho.nsa.gov> wrote:
> On 05/08/2018 08:25 PM, Paul Moore wrote:
>> On Tue, May 8, 2018 at 2:40 PM, Stephen Smalley <sds@...ho.nsa.gov> wrote:
>>> On 05/08/2018 01:05 PM, Paul Moore wrote:
>>>> On Tue, May 8, 2018 at 10:05 AM, Alexey Kodanev
>>>> <alexey.kodanev@...cle.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@...cle.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.
>>
>> Yes I know, I thought I was the one that suggested it at some point
>> (I'll take the blame) ... although now that I'm looking at the git
>> log, maybe I'm confusing it with something else.
>>
>>>> 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?
>>
>> I believe these name_bind permission checkis skipped for AF_UNSPEC
>> already, isn't it? The only way the name_bind check would be
>> triggered is if the source port, snum, was non-zero and I didn't think
>> that was really legal for AF_UNSPEC/INADDR_ANY, is it?
>
> 1) What in inet_bind() prevents that from occurring?
> 2) Regardless, what about the node_bind check?
Fair enough. As mentioned above, perhaps the right fix is to move the
address family checking back to how it was pre-SCTP.
Alexey, is this something you want to do, or should we take care of that?
>>>> 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
>>>>>
>>>>
>>>
>>
>>
>>
>
--
paul moore
www.paul-moore.com
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