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Message-ID: <7fdbaf13-fea2-4a2c-213d-fa291db67081@tycho.nsa.gov>
Date: Wed, 9 May 2018 08:37:19 -0400
From: Stephen Smalley <sds@...ho.nsa.gov>
To: Paul Moore <paul@...l-moore.com>
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 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?
>
>>> 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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