On 03/08/07 13:09, Evgeniy Polyakov wrote:
> On Fri, Aug 03, 2007 at 01:03:46PM +0100, Simon Arlott ([EMAIL PROTECTED])
> wrote:
>> On Fri, August 3, 2007 12:56, Evgeniy Polyakov wrote:
>> > On Fri, Aug 03, 2007 at 12:21:46PM +0100, Simon Arlott ([EMAIL PROTECTED])
>> > wrote:
>> >> Since the connection is considered closed, couldn't another socket re-use
>> >> it?
>> >>
>> >> Socket A: Recv data (unread)
>> >> Socket A: Recv RST
>> >> Socket B: Reuses connection (same IPs/ports)
>> >> Socket A: Close
>> >>
>> >> Wouldn't that disrupt socket B's use of the connection?
>> >
>> > Then it will drop our data, since there were no appropriate handhsake.
>>
>> Couldn't the sequence numbers be close enough to make the RST valid?
>
> It does not matter - if connection is not in synchronized state all
> unrelated data is dropped, so remote side is only allowed to receive syn
> flag only, anything else must be dropped. If remote side does not do
> that, it violates RFC.
Except the remote side has a connection, because another one can be made
before the existing connection is closed:
17:37:37.377571 IP 192.168.7.4.50550 > 192.168.7.8.2500: S
134077329:134077329(0) win 1500 (raw)
17:37:37.382352 IP 192.168.7.8.2500 > 192.168.7.4.50550: S
3460060233:3460060233(0) ack 134077330 win 14360 <mss 7180> (accept)
17:37:37.377966 IP 192.168.7.4.50550 > 192.168.7.8.2500: . ack 1 win 1500 (raw)
17:37:37.378128 IP 192.168.7.4.50550 > 192.168.7.8.2500: P 1:17(16) ack 1 win
1500 (raw)
17:37:37.378162 IP 192.168.7.8.2500 > 192.168.7.4.50550: . ack 17 win 14360
17:37:37.378131 IP 192.168.7.4.50550 > 192.168.7.8.2500: R
134077346:134077346(0) win 1500 (raw)
17:37:37.412709 IP 192.168.7.4.50550 > 192.168.7.8.2500: SWE
3257207813:3257207813(0) win 14280 <mss 7140,sackOK,timestamp 3601441543
0,nop,wscale 5> (connect)
17:37:37.412785 IP 192.168.7.8.2500 > 192.168.7.4.50550: SE
3495384256:3495384256(0) ack 3257207814 win 14336 <mss 7180,sackOK,timestamp
4294812905 3601441543,nop,wscale 6> (accept)
17:37:37.412960 IP 192.168.7.4.50550 > 192.168.7.8.2500: . ack 1 win 447
<nop,nop,timestamp 3601441543 4294812905>
17:37:38.383085 IP 192.168.7.8.2500 > 192.168.7.4.50550: R
4259643274:4259643274(0) ack 1171836829 win 14360 (close (previous connection))
17:37:47.417649 IP 192.168.7.8.2500 > 192.168.7.4.50550: F 1:1(0) ack 1 win 224
<nop,nop,timestamp 4294822910 3601441543> (close)
17:37:47.417993 IP 192.168.7.4.50550 > 192.168.7.8.2500: F 1:1(0) ack 2 win 447
<nop,nop,timestamp 3601444045 4294822910> (read returned)
17:37:47.418466 IP 192.168.7.8.2500 > 192.168.7.4.50550: . ack 2 win 224
<nop,nop,timestamp 4294822911 3601444045>
The second connection also modified the RST|ACK that was sent compared to no
second connection:
17:38:03.532703 IP 192.168.7.4.50550 > 192.168.7.8.2500: S 82517575:82517575(0)
win 1500 (raw)
17:38:03.532832 IP 192.168.7.8.2500 > 192.168.7.4.50550: S
3495449795:3495449795(0) ack 82517576 win 14360 <mss 7180> (accept)
17:38:03.533388 IP 192.168.7.4.50550 > 192.168.7.8.2500: . ack 1 win 1500 (raw)
17:38:03.533457 IP 192.168.7.4.50550 > 192.168.7.8.2500: P 1:17(16) ack 1 win
1500 (raw)
17:38:03.533597 IP 192.168.7.8.2500 > 192.168.7.4.50550: . ack 17 win 14360
17:38:03.533589 IP 192.168.7.4.50550 > 192.168.7.8.2500: R 82517592:82517592(0)
win 1500 (raw)
17:38:04.536277 IP 192.168.7.8.2500 > 192.168.7.4.50550: R 1:1(0) ack 17 win
14360 (close)
17:38:04.536277 IP 192.168.7.8.2500 > 192.168.7.4.50550: R 1:1(0) ack 17 win
14360
vs
17:37:38.383085 IP 192.168.7.8.2500 > 192.168.7.4.50550: R
4259643274:4259643274(0) ack 1171836829 win 14360
What happened there ?
On the server, run tcptest-server.c, which waits for 1s on the first connection
then 10s on the second connection.
On the client, run:
iptables -I INPUT -i eth0 -p tcp --dport 50550 -j DROP; ./client; iptables -D
INPUT -i eth0 -p tcp --dport 50550 -j DROP; ./tcptest-client
(client.c from john's original email)
--
Simon Arlott
#include <sys/types.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <poll.h>
#include <fcntl.h>
#define PORT 2500
#define xerror(str) do { perror(str); exit(1); } while (0)
int main(void) {
struct sockaddr_in sa;
int l, s, tmp;
int t = 0;
memset(&sa, 0, sizeof(sa));
l = socket(PF_INET, SOCK_STREAM, IPPROTO_TCP);
if (!l)
xerror("socket");
sa.sin_family = AF_INET;
sa.sin_addr.s_addr = htonl(INADDR_ANY);
sa.sin_port = htons(PORT);
tmp = 1;
setsockopt(l, SOL_SOCKET, SO_REUSEADDR, (char*)&tmp, sizeof(tmp));
if (bind(l, (struct sockaddr*)&sa, sizeof(sa)) != 0)
xerror("bind");
if (listen(l, 0) != 0)
xerror("listen");
printf("server %d ready...\n", getpid());
for (t = 1; t <= 2; t++) {
s = accept(l, NULL, NULL);
switch (fork()) {
case -1:
xerror("fork");
break;
case 0:
switch (t) {
case 1:
printf("server %d accepted connection\n", getpid());
#if 0
tmp = fcntl(s, F_GETFL, 0);
if (fcntl(s, F_SETFL, tmp | O_NONBLOCK) != 0)
xerror("fcntl");
if (send(s, "AAAAAAA", 7, 0) != 7)
xerror("send");
#endif
printf("server %d waiting for 1 second...\n", getpid());
sleep(1);
printf("server %d closing connection\n", getpid());
close(s);
return 0;
break;
case 2:
printf("server %d accepted connection\n", getpid());
printf("server %d waiting for 10 seconds...\n", getpid());
sleep(10);
printf("server %d closing connection\n", getpid());
close(s);
return 0;
break;
}
break;
default:
close(s);
}
}
wait(NULL);
wait(NULL);
return 0;
}
#include <sys/types.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#define SERVER_IP "192.168.7.8"
#define SRC_PORT 50550
#define DST_PORT 2500
#define xerror(str) do { perror(str); exit(1); } while (0)
int main(void) {
struct sockaddr_in sa;
int s;
int t = 0;
char buf[32];
int ret, tmp;
memset(&sa, 0, sizeof(sa));
for (t = 1; t <= 1; t++) {
switch (fork()) {
case -1:
xerror("fork");
break;
case 0:
printf("client %d binding port...\n", getpid());
s = socket(PF_INET, SOCK_STREAM, IPPROTO_TCP);
if (!s)
xerror("socket");
sa.sin_family = AF_INET;
sa.sin_addr.s_addr = htonl(INADDR_ANY);
sa.sin_port = htons(SRC_PORT);
tmp = 1;
if (setsockopt(s, SOL_SOCKET, SO_REUSEADDR, (char*)&tmp, sizeof(tmp)) != 0)
xerror("setsockopt");
if (bind(s, (struct sockaddr*)&sa, sizeof(sa)) != 0)
xerror("bind");
printf("client %d connecting...\n", getpid());
sa.sin_family = AF_INET;
sa.sin_addr.s_addr = inet_addr(SERVER_IP);
sa.sin_port = htons(DST_PORT);
if (connect(s, (struct sockaddr*)&sa, sizeof(sa)) != 0)
xerror("connect");
printf("client %d waiting in read()...\n", getpid());
ret = read(s, buf, 32);
printf("client %d read() returned %d\n", getpid(), ret);
close(s);
return 0;
}
wait(NULL);
}
return 0;
}
