* Fw: [Bug 102051] New: Unexpected TCP behavior
@ 2015-07-27 21:02 Stephen Hemminger
2015-07-27 21:35 ` Eric Dumazet
0 siblings, 1 reply; 2+ messages in thread
From: Stephen Hemminger @ 2015-07-27 21:02 UTC (permalink / raw)
To: netdev
Begin forwarded message:
Date: Mon, 27 Jul 2015 20:06:07 +0000
From: "bugzilla-daemon@bugzilla.kernel.org" <bugzilla-daemon@bugzilla.kernel.org>
To: "shemminger@linux-foundation.org" <shemminger@linux-foundation.org>
Subject: [Bug 102051] New: Unexpected TCP behavior
https://bugzilla.kernel.org/show_bug.cgi?id=102051
Bug ID: 102051
Summary: Unexpected TCP behavior
Product: Networking
Version: 2.5
Kernel Version: 3.19
Hardware: All
OS: Linux
Tree: Mainline
Status: NEW
Severity: low
Priority: P1
Component: IPV4
Assignee: shemminger@linux-foundation.org
Reporter: vremetic@gmail.com
Regression: No
While running nmap against localhost I started to see open ports in the dynamic
range (>1024). Kind of odd, knowing netstat and ss did not show any listeners
on the port.
With tcpdump, I confirmed system was returning S/ACK for ports that did not
have a listener enabled. The "issue" or feature only occurs if source port
matches the destination port.
# netstat -nap | grep 5000
#
$ nc localhost -p 5000 5000
a
a
# tcpdump -i lo port 5000
14:28:18.059708 IP 127.0.0.1.5000 > 127.0.0.1.5000: Flags [S], seq 2005295207,
win 43690, options [mss 65495,sackOK,TS val 4481790 ecr 0,nop,wscale 7], length
0
14:28:18.059721 IP 127.0.0.1.5000 > 127.0.0.1.5000: Flags [S.], seq 2005295207,
ack 2005295208, win 43690, options [mss 65495,sackOK,TS val 4481790 ecr
4481790,nop,wscale 7], length 0
14:28:18.059729 IP 127.0.0.1.5000 > 127.0.0.1.5000: Flags [.], ack 2005295208,
win 342, options [nop,nop,TS val 4481790 ecr 4481790], length 0
14:28:19.121392 IP 127.0.0.1.5000 > 127.0.0.1.5000: Flags [P.], seq
2005295208:2005295210, ack 2005295208, win 342, options [nop,nop,TS val 4482056
ecr 4481790], length 2
14:28:19.121407 IP 127.0.0.1.5000 > 127.0.0.1.5000: Flags [.], ack 2005295210,
win 342, options [nop,nop,TS val 4482056 ecr 4482056], length 0
# hping3 -S 127.0.0.1 -p 5000 -s 5000
HPING 127.0.0.1 (lo 127.0.0.1): S set, 40 headers + 0 data bytes
len=40 ip=127.0.0.1 ttl=64 id=2036 sport=5000 flags=S seq=0 win=512 rtt=3.8 ms
<< SYN
DUP! len=52 ip=127.0.0.1 ttl=64 DF id=670 sport=5000 flags=A seq=0 win=342
rtt=3.8 ms << SYN/ACK
len=40 ip=127.0.0.1 ttl=64 DF id=43435 sport=5000 flags=RA seq=1 win=0 rtt=3.7
ms
I confirmed it with nmap, nc, and hping3; granted they build on same c
libraries, so I am not even sure if this should be filed as a kernel bug (or
even a bug);
just did not expect to see this behavior //
Expected to see a RST instead.
--
You are receiving this mail because:
You are the assignee for the bug.
^ permalink raw reply [flat|nested] 2+ messages in thread
* Re: Fw: [Bug 102051] New: Unexpected TCP behavior
2015-07-27 21:02 Fw: [Bug 102051] New: Unexpected TCP behavior Stephen Hemminger
@ 2015-07-27 21:35 ` Eric Dumazet
0 siblings, 0 replies; 2+ messages in thread
From: Eric Dumazet @ 2015-07-27 21:35 UTC (permalink / raw)
To: Stephen Hemminger; +Cc: netdev
On Mon, 2015-07-27 at 14:02 -0700, Stephen Hemminger wrote:
>
> Begin forwarded message:
>
> Date: Mon, 27 Jul 2015 20:06:07 +0000
> From: "bugzilla-daemon@bugzilla.kernel.org" <bugzilla-daemon@bugzilla.kernel.org>
> To: "shemminger@linux-foundation.org" <shemminger@linux-foundation.org>
> Subject: [Bug 102051] New: Unexpected TCP behavior
>
>
> https://bugzilla.kernel.org/show_bug.cgi?id=102051
>
> Bug ID: 102051
> Summary: Unexpected TCP behavior
> Product: Networking
> Version: 2.5
> Kernel Version: 3.19
> Hardware: All
> OS: Linux
> Tree: Mainline
> Status: NEW
> Severity: low
> Priority: P1
> Component: IPV4
> Assignee: shemminger@linux-foundation.org
> Reporter: vremetic@gmail.com
> Regression: No
>
> While running nmap against localhost I started to see open ports in the dynamic
> range (>1024). Kind of odd, knowing netstat and ss did not show any listeners
> on the port.
>
> With tcpdump, I confirmed system was returning S/ACK for ports that did not
> have a listener enabled. The "issue" or feature only occurs if source port
> matches the destination port.
>
> # netstat -nap | grep 5000
> #
>
> $ nc localhost -p 5000 5000
> a
> a
>
> # tcpdump -i lo port 5000
> 14:28:18.059708 IP 127.0.0.1.5000 > 127.0.0.1.5000: Flags [S], seq 2005295207,
> win 43690, options [mss 65495,sackOK,TS val 4481790 ecr 0,nop,wscale 7], length
> 0
> 14:28:18.059721 IP 127.0.0.1.5000 > 127.0.0.1.5000: Flags [S.], seq 2005295207,
> ack 2005295208, win 43690, options [mss 65495,sackOK,TS val 4481790 ecr
> 4481790,nop,wscale 7], length 0
Nothing wrong here. This is well known TCP behavior ( cross syn ).
> 14:28:18.059729 IP 127.0.0.1.5000 > 127.0.0.1.5000: Flags [.], ack 2005295208,
> win 342, options [nop,nop,TS val 4481790 ecr 4481790], length 0
> 14:28:19.121392 IP 127.0.0.1.5000 > 127.0.0.1.5000: Flags [P.], seq
> 2005295208:2005295210, ack 2005295208, win 342, options [nop,nop,TS val 4482056
> ecr 4481790], length 2
> 14:28:19.121407 IP 127.0.0.1.5000 > 127.0.0.1.5000: Flags [.], ack 2005295210,
> win 342, options [nop,nop,TS val 4482056 ecr 4482056], length 0
>
> # hping3 -S 127.0.0.1 -p 5000 -s 5000
> HPING 127.0.0.1 (lo 127.0.0.1): S set, 40 headers + 0 data bytes
> len=40 ip=127.0.0.1 ttl=64 id=2036 sport=5000 flags=S seq=0 win=512 rtt=3.8 ms
> << SYN
> DUP! len=52 ip=127.0.0.1 ttl=64 DF id=670 sport=5000 flags=A seq=0 win=342
> rtt=3.8 ms << SYN/ACK
> len=40 ip=127.0.0.1 ttl=64 DF id=43435 sport=5000 flags=RA seq=1 win=0 rtt=3.7
> ms
>
> I confirmed it with nmap, nc, and hping3; granted they build on same c
> libraries, so I am not even sure if this should be filed as a kernel bug (or
> even a bug);
> just did not expect to see this behavior //
>
> Expected to see a RST instead.
>
Sigh.
Wont fix.
^ permalink raw reply [flat|nested] 2+ messages in thread
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2015-07-27 21:35 ` Eric Dumazet
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