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Message-ID: <CADvbK_cLGA4PH_c4FB0eSUAMoV0XgtyA++cTFsGDkb=nvtR68g@mail.gmail.com>
Date: Fri, 20 Oct 2017 21:14:55 +0800
From: Xin Long <lucien.xin@...il.com>
To: Richard Haines <richard_c_haines@...nternet.com>
Cc: Neil Horman <nhorman@...driver.com>, selinux@...ho.nsa.gov,
network dev <netdev@...r.kernel.org>,
linux-sctp@...r.kernel.org, linux-security-module@...r.kernel.org
Subject: Re: [RFC PATCH 3/5] sctp: Add LSM hooks
On Fri, Oct 20, 2017 at 8:04 PM, Richard Haines
<richard_c_haines@...nternet.com> wrote:
> On Fri, 2017-10-20 at 07:16 -0400, Neil Horman wrote:
>> On Wed, Oct 18, 2017 at 11:05:09PM +0800, Xin Long wrote:
>> > On Tue, Oct 17, 2017 at 9:58 PM, Richard Haines
>> > <richard_c_haines@...nternet.com> wrote:
>> > > Add security hooks to allow security modules to exercise access
>> > > control
>> > > over SCTP.
>> > >
>> > > Signed-off-by: Richard Haines <richard_c_haines@...nternet.com>
>> > > ---
>> > > include/net/sctp/structs.h | 10 ++++++++
>> > > include/uapi/linux/sctp.h | 1 +
>> > > net/sctp/sm_make_chunk.c | 12 +++++++++
>> > > net/sctp/sm_statefuns.c | 14 ++++++++++-
>> > > net/sctp/socket.c | 61
>> > > +++++++++++++++++++++++++++++++++++++++++++++-
>> > > 5 files changed, 96 insertions(+), 2 deletions(-)
>> > >
>> > > diff --git a/include/net/sctp/structs.h
>> > > b/include/net/sctp/structs.h
>> > > index 7767577..6e72e3e 100644
>> > > --- a/include/net/sctp/structs.h
>> > > +++ b/include/net/sctp/structs.h
>> > > @@ -1270,6 +1270,16 @@ struct sctp_endpoint {
>> > > reconf_enable:1;
>> > >
>> > > __u8 strreset_enable;
>> > > +
>> > > + /* Security identifiers from incoming (INIT). These are
>> > > set by
>> > > + * security_sctp_assoc_request(). These will only be used
>> > > by
>> > > + * SCTP TCP type sockets and peeled off connections as
>> > > they
>> > > + * cause a new socket to be generated.
>> > > security_sctp_sk_clone()
>> > > + * will then plug these into the new socket.
>> > > + */
>> > > +
>> > > + u32 secid;
>> > > + u32 peer_secid;
>> > > };
>> > >
>> > > /* Recover the outter endpoint structure. */
>> > > diff --git a/include/uapi/linux/sctp.h
>> > > b/include/uapi/linux/sctp.h
>> > > index 6217ff8..c04812f 100644
>> > > --- a/include/uapi/linux/sctp.h
>> > > +++ b/include/uapi/linux/sctp.h
>> > > @@ -122,6 +122,7 @@ typedef __s32 sctp_assoc_t;
>> > > #define SCTP_RESET_ASSOC 120
>> > > #define SCTP_ADD_STREAMS 121
>> > > #define SCTP_SOCKOPT_PEELOFF_FLAGS 122
>> > > +#define SCTP_SENDMSG_CONNECT 123
>> > >
>> > > /* PR-SCTP policies */
>> > > #define SCTP_PR_SCTP_NONE 0x0000
>> > > diff --git a/net/sctp/sm_make_chunk.c b/net/sctp/sm_make_chunk.c
>> > > index 6110447..ca4705b 100644
>> > > --- a/net/sctp/sm_make_chunk.c
>> > > +++ b/net/sctp/sm_make_chunk.c
>> > > @@ -3059,6 +3059,12 @@ static __be16
>> > > sctp_process_asconf_param(struct sctp_association *asoc,
>> > > if (af->is_any(&addr))
>> > > memcpy(&addr, &asconf->source,
>> > > sizeof(addr));
>> > >
>> > > + if (security_sctp_bind_connect(asoc->ep->base.sk,
>> > > + SCTP_PARAM_ADD_IP,
>> > > + (struct sockaddr
>> > > *)&addr,
>> > > + af->sockaddr_len))
>> > > + return SCTP_ERROR_REQ_REFUSED;
>> > > +
>> > > /* ADDIP 4.3 D9) If an endpoint receives an ADD
>> > > IP address
>> > > * request and does not have the local resources
>> > > to add this
>> > > * new address to the association, it MUST return
>> > > an Error
>> > > @@ -3125,6 +3131,12 @@ static __be16
>> > > sctp_process_asconf_param(struct sctp_association *asoc,
>> > > if (af->is_any(&addr))
>> > > memcpy(&addr.v4, sctp_source(asconf),
>> > > sizeof(addr));
>> > >
>> > > + if (security_sctp_bind_connect(asoc->ep->base.sk,
>> > > + SCTP_PARAM_SET_PRI
>> > > MARY,
>> > > + (struct sockaddr
>> > > *)&addr,
>> > > + af->sockaddr_len))
>> > > + return SCTP_ERROR_REQ_REFUSED;
>> > > +
>> > > peer = sctp_assoc_lookup_paddr(asoc, &addr);
>> > > if (!peer)
>> > > return SCTP_ERROR_DNS_FAILED;
>> > > diff --git a/net/sctp/sm_statefuns.c b/net/sctp/sm_statefuns.c
>> > > index b2a74c3..4ba5805 100644
>> > > --- a/net/sctp/sm_statefuns.c
>> > > +++ b/net/sctp/sm_statefuns.c
>> > > @@ -314,6 +314,11 @@ sctp_disposition_t
>> > > sctp_sf_do_5_1B_init(struct net *net,
>> > > sctp_unrecognized_param_t *unk_param;
>> > > int len;
>> > >
>> > > + /* Update socket peer label if first association. */
>> > > + if (security_sctp_assoc_request((struct sctp_endpoint
>> > > *)ep,
>> > > + chunk->skb,
>> > > SCTP_CID_INIT))
>> > > + return sctp_sf_pdiscard(net, ep, asoc, type, arg,
>> > > commands);
>> > > +
>> > > /* 6.10 Bundling
>> > > * An endpoint MUST NOT bundle INIT, INIT ACK or
>> > > * SHUTDOWN COMPLETE with any other chunks.
>> > > @@ -446,7 +451,6 @@ sctp_disposition_t
>> > > sctp_sf_do_5_1B_init(struct net *net,
>> > > }
>> > >
>> > > sctp_add_cmd_sf(commands, SCTP_CMD_NEW_ASOC,
>> > > SCTP_ASOC(new_asoc));
>> > > -
>> > > sctp_add_cmd_sf(commands, SCTP_CMD_REPLY,
>> > > SCTP_CHUNK(repl));
>> > >
>> > > /*
>> > > @@ -507,6 +511,11 @@ sctp_disposition_t
>> > > sctp_sf_do_5_1C_ack(struct net *net,
>> > > struct sctp_chunk *err_chunk;
>> > > struct sctp_packet *packet;
>> > >
>> > > + /* Update socket peer label if first association. */
>> > > + if (security_sctp_assoc_request((struct sctp_endpoint
>> > > *)ep,
>> > > + chunk->skb,
>> > > SCTP_CID_INIT_ACK))
>> > > + return sctp_sf_pdiscard(net, ep, asoc, type, arg,
>> > > commands);
>> > > +
>> >
>> > Just thinking security_sctp_assoc_request hook should also be in
>> > sctp_sf_do_unexpected_init() and sctp_sf_do_5_2_4_dupcook() ?
>>
>> I agree, i think if this hook is gating on the creation of a new
>> association,
>> they should be in all the locations where that happens
>> Neil
>
> Thanks for the comments. I've just added the hook as requested for my
> next update, however I have not managed to trigger these areas using
> the lksctp-tools tests. Can you suggest any suitable tools for testing
> these scenarios.
It's all a matter of timing:
sctp_sf_do_5_2_2_dupinit():
Case A:
Endpoint A Endpoint B ULP
(CLOSED) (CLOSED)
INIT ----------------->
<----------------- INIT-ACK
COOKIE-ECHO ----------------->
<----------------- COOKIE-ACK
Communication Up ---------->
INIT ----------------->
(Different INIT-TAG)
<----------------- INIT-ACK
COOKIE-ECHO ----------------->
<----------------- COOKIE-ACK
DATA ----------------->
<----------------- SACK
sctp_sf_do_5_2_1_siminit():
Case B:
Endpoint A Endpoint B ULP
(CLOSED) (CLOSED)
<----- Associate
<----------------- INIT
INIT ----------------->
<----------------- INIT-ACK
COOKIE-ECHO ----------------->
<----------------- COOKIE-ACK
Communication Up ---------->
sctp_sf_do_5_2_4_dupcook():
Case D:
Endpoint A Endpoint B ULP
(CLOSED) (CLOSED)
<----- Associate
INIT ----------------->
<----------------- INIT-ACK
COOKIE-ECHO ----------------->
<----------------- COOKIE-ACK
Communication Up ---------->
COOKIE-ECHO ----------------->
<----------------- COOKIE-ACK
I think scapy could help with 4-shake stuff:
# iptables -A OUTPUT -p sctp -d 192.0.0.2 --chunk-type only abort -o
eth1 -j DROP
and
something like:
def start_assoc(self, target, local):
target_host, target_port = target
local_host, local_port = local
# init snd
self._tsn = 2017
self._cnt = 15
SCTP_HEADER = (IP(dst=target_host, flags="DF") /
SCTP(sport=local_port, dport=target_port, tag=0))
INIT = (SCTP_HEADER / SCTPChunkInit(init_tag=1,
a_rwnd=106496, n_out_streams=self._cnt, n_in_streams=self._cnt,
init_tsn=self._tsn,
params=[SCTPParamSupport(types=[64])]))
INIT_ACK = sr1(INIT, timeout=3, verbose=0)
if INIT_ACK == None or not INIT_ACK.haslayer(SCTPChunkInitAck):
return False
# cookie echo snd
SCTP_HEADER[SCTP].tag = INIT_ACK[SCTPChunkInitAck].init_tag
COOKIE_ECHO = (SCTP_HEADER /
SCTPChunkCookieEcho(cookie=INIT_ACK[SCTPChunkParamStateCookie].cookie))
COOKIE_ACK = sr1(COOKIE_ECHO, timeout=3, verbose=0)
if COOKIE_ACK == None or not
COOKIE_ACK.haslayer(SCTPChunkCookieAck):
return False
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