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Message-ID: <CAHC9VhSg9UAmXaK0xsy_h9HfzM4uUBqCNKN5qtf3hHLSi=ZENw@mail.gmail.com>
Date: Wed, 9 May 2018 11:34:11 -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 11:11 AM, Stephen Smalley <sds@...ho.nsa.gov> wrote:
> On 05/09/2018 11:01 AM, Paul Moore wrote:
>> 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.
>
> It isn't clear to me how to do that without breaking SCTP multiple address binding, which is why
> Richard had to switch to checking address->sa_family instead of just using the sk->sk_family.
> Alexey's original fix might be the simplest solution.
I'm going to have to apologize, I'm traveling at the moment and more
distracted than usual as a result. Let me take a closer look later
today. It may be that Alexey's original fix the only practical
solution, but I really would like to avoid having to duplicate checks
like that in the SELinux code.
>> 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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