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authorDaniel Borkmann <dborkman@redhat.com>2015-01-15 16:34:35 +0100
committerDavid S. Miller <davem@davemloft.net>2015-01-17 23:52:20 -0500
commit2061dcd6bff8b774b4fac8b0739b6be3f87bc9f2 (patch)
treeb9252f5648efa423d813a9eeaf35dd44944990c9
parentee1c244219fd652964710a6cc3e4f922e86aa492 (diff)
downloadkernel-2061dcd6bff8b774b4fac8b0739b6be3f87bc9f2.tar.gz
net: sctp: fix race for one-to-many sockets in sendmsg's auto associate
I.e. one-to-many sockets in SCTP are not required to explicitly call into connect(2) or sctp_connectx(2) prior to data exchange. Instead, they can directly invoke sendmsg(2) and the SCTP stack will automatically trigger connection establishment through 4WHS via sctp_primitive_ASSOCIATE(). However, this in its current implementation is racy: INIT is being sent out immediately (as it cannot be bundled anyway) and the rest of the DATA chunks are queued up for later xmit when connection is established, meaning sendmsg(2) will return successfully. This behaviour can result in an undesired side-effect that the kernel made the application think the data has already been transmitted, although none of it has actually left the machine, worst case even after close(2)'ing the socket. Instead, when the association from client side has been shut down e.g. first gracefully through SCTP_EOF and then close(2), the client could afterwards still receive the server's INIT_ACK due to a connection with higher latency. This INIT_ACK is then considered out of the blue and hence responded with ABORT as there was no alive assoc found anymore. This can be easily reproduced f.e. with sctp_test application from lksctp. One way to fix this race is to wait for the handshake to actually complete. The fix defers waiting after sctp_primitive_ASSOCIATE() and sctp_primitive_SEND() succeeded, so that DATA chunks cooked up from sctp_sendmsg() have already been placed into the output queue through the side-effect interpreter, and therefore can then be bundeled together with COOKIE_ECHO control chunks. strace from example application (shortened): socket(PF_INET, SOCK_SEQPACKET, IPPROTO_SCTP) = 3 sendmsg(3, {msg_name(28)={sa_family=AF_INET, sin_port=htons(8888), sin_addr=inet_addr("192.168.1.115")}, msg_iov(1)=[{"hello", 5}], msg_controllen=0, msg_flags=0}, 0) = 5 sendmsg(3, {msg_name(28)={sa_family=AF_INET, sin_port=htons(8888), sin_addr=inet_addr("192.168.1.115")}, msg_iov(1)=[{"hello", 5}], msg_controllen=0, msg_flags=0}, 0) = 5 sendmsg(3, {msg_name(28)={sa_family=AF_INET, sin_port=htons(8888), sin_addr=inet_addr("192.168.1.115")}, msg_iov(1)=[{"hello", 5}], msg_controllen=0, msg_flags=0}, 0) = 5 sendmsg(3, {msg_name(28)={sa_family=AF_INET, sin_port=htons(8888), sin_addr=inet_addr("192.168.1.115")}, msg_iov(1)=[{"hello", 5}], msg_controllen=0, msg_flags=0}, 0) = 5 sendmsg(3, {msg_name(28)={sa_family=AF_INET, sin_port=htons(8888), sin_addr=inet_addr("192.168.1.115")}, msg_iov(0)=[], msg_controllen=48, {cmsg_len=48, cmsg_level=0x84 /* SOL_??? */, cmsg_type=, ...}, msg_flags=0}, 0) = 0 // graceful shutdown for SOCK_SEQPACKET via SCTP_EOF close(3) = 0 tcpdump before patch (fooling the application): 22:33:36.306142 IP 192.168.1.114.41462 > 192.168.1.115.8888: sctp (1) [INIT] [init tag: 3879023686] [rwnd: 106496] [OS: 10] [MIS: 65535] [init TSN: 3139201684] 22:33:36.316619 IP 192.168.1.115.8888 > 192.168.1.114.41462: sctp (1) [INIT ACK] [init tag: 3345394793] [rwnd: 106496] [OS: 10] [MIS: 10] [init TSN: 3380109591] 22:33:36.317600 IP 192.168.1.114.41462 > 192.168.1.115.8888: sctp (1) [ABORT] tcpdump after patch: 14:28:58.884116 IP 192.168.1.114.35846 > 192.168.1.115.8888: sctp (1) [INIT] [init tag: 438593213] [rwnd: 106496] [OS: 10] [MIS: 65535] [init TSN: 3092969729] 14:28:58.888414 IP 192.168.1.115.8888 > 192.168.1.114.35846: sctp (1) [INIT ACK] [init tag: 381429855] [rwnd: 106496] [OS: 10] [MIS: 10] [init TSN: 2141904492] 14:28:58.888638 IP 192.168.1.114.35846 > 192.168.1.115.8888: sctp (1) [COOKIE ECHO] , (2) [DATA] (B)(E) [TSN: 3092969729] [...] 14:28:58.893278 IP 192.168.1.115.8888 > 192.168.1.114.35846: sctp (1) [COOKIE ACK] , (2) [SACK] [cum ack 3092969729] [a_rwnd 106491] [#gap acks 0] [#dup tsns 0] 14:28:58.893591 IP 192.168.1.114.35846 > 192.168.1.115.8888: sctp (1) [DATA] (B)(E) [TSN: 3092969730] [...] 14:28:59.096963 IP 192.168.1.115.8888 > 192.168.1.114.35846: sctp (1) [SACK] [cum ack 3092969730] [a_rwnd 106496] [#gap acks 0] [#dup tsns 0] 14:28:59.097086 IP 192.168.1.114.35846 > 192.168.1.115.8888: sctp (1) [DATA] (B)(E) [TSN: 3092969731] [...] , (2) [DATA] (B)(E) [TSN: 3092969732] [...] 14:28:59.103218 IP 192.168.1.115.8888 > 192.168.1.114.35846: sctp (1) [SACK] [cum ack 3092969732] [a_rwnd 106486] [#gap acks 0] [#dup tsns 0] 14:28:59.103330 IP 192.168.1.114.35846 > 192.168.1.115.8888: sctp (1) [SHUTDOWN] 14:28:59.107793 IP 192.168.1.115.8888 > 192.168.1.114.35846: sctp (1) [SHUTDOWN ACK] 14:28:59.107890 IP 192.168.1.114.35846 > 192.168.1.115.8888: sctp (1) [SHUTDOWN COMPLETE] Looks like this bug is from the pre-git history museum. ;) Fixes: 08707d5482df ("lksctp-2_5_31-0_5_1.patch") Signed-off-by: Daniel Borkmann <dborkman@redhat.com> Acked-by: Vlad Yasevich <vyasevich@gmail.com> Signed-off-by: David S. Miller <davem@davemloft.net>
-rw-r--r--net/sctp/socket.c8
1 files changed, 7 insertions, 1 deletions
diff --git a/net/sctp/socket.c b/net/sctp/socket.c
index 2625eccb77d5..aafe94bf292e 100644
--- a/net/sctp/socket.c
+++ b/net/sctp/socket.c
@@ -1603,7 +1603,7 @@ static int sctp_sendmsg(struct kiocb *iocb, struct sock *sk,
sctp_assoc_t associd = 0;
sctp_cmsgs_t cmsgs = { NULL };
sctp_scope_t scope;
- bool fill_sinfo_ttl = false;
+ bool fill_sinfo_ttl = false, wait_connect = false;
struct sctp_datamsg *datamsg;
int msg_flags = msg->msg_flags;
__u16 sinfo_flags = 0;
@@ -1943,6 +1943,7 @@ static int sctp_sendmsg(struct kiocb *iocb, struct sock *sk,
if (err < 0)
goto out_free;
+ wait_connect = true;
pr_debug("%s: we associated primitively\n", __func__);
}
@@ -1980,6 +1981,11 @@ static int sctp_sendmsg(struct kiocb *iocb, struct sock *sk,
sctp_datamsg_put(datamsg);
err = msg_len;
+ if (unlikely(wait_connect)) {
+ timeo = sock_sndtimeo(sk, msg_flags & MSG_DONTWAIT);
+ sctp_wait_for_connect(asoc, &timeo);
+ }
+
/* If we are already past ASSOCIATE, the lower
* layers are responsible for association cleanup.
*/