[Pkg-samba-maint] Bug#856843: Bug#856843: smbclient: connection flood to port 445 on mounting cifs volume under kernel 4.9.0

[Jelmer Vernooij]

On Sun, Mar 05, 2017 at 12:30:33PM +0100, nils wrote:
> Package: smbclient
> Version: 2:4.2.14+dfsg-0+deb8u2
> Severity: important
> 
> Hello,
> after upgrading my kernel from 4.0.8 to 4.0.9 I am getting connection floods to
> my FreeNAS samba server from my debian machine. I never had this issue with
> 4.0.8
> 
> Linux dnet64 4.9.0-0.bpo.1-amd64 #1 SMP Debian 4.9.2-2~bpo8+1 (2017-01-26)
> x86_64 GNU/Linux
> ii  smbclient  2:4.2.14+dfsg-0+deb8u2               amd64        command-line
> SMB/CIFS clients for Unix
> 
> After mouting the cifs share(s) everything is OK for about 10 minutes, then a
> flood of connections happens. Here is an extract of 'netstat -an' run every
> second. Only one or two connections are shown for every 'netstat -an' run. The
> connections are opening and closing at an incredible speed (nethogs goes to
> 100% and doesn't show anything because it's overwhelmed). gkrellm reports about
> 70k/Sec traffic due to this. See how the source port numbers increase
> increadibly quickly to get an idea of how many connections are really
> happening...
> ....
> tcp        0      1 10.0.2.15:55044         192.168.2.88:445        SYN_SENT
> tcp        0      1 10.0.2.15:55252         192.168.2.88:445        SYN_SENT
> tcp        0      0 10.0.2.15:55288         192.168.2.88:445        ESTABLISHED
> tcp        0      1 10.0.2.15:55314         192.168.2.88:445        SYN_SENT
> tcp        0      1 10.0.2.15:55348         192.168.2.88:445        SYN_SENT
> tcp        0      0 10.0.2.15:55396         192.168.2.88:445        ESTABLISHED
> tcp        0      1 10.0.2.15:55454         192.168.2.88:445        SYN_SENT
> tcp        0      0 10.0.2.15:55500         192.168.2.88:445        ESTABLISHED
> tcp        0      0 10.0.2.15:55544         192.168.2.88:445        ESTABLISHED
> tcp        0     42 10.0.2.15:55586         192.168.2.88:445        ESTABLISHED
> tcp        0      0 10.0.2.15:55630         192.168.2.88:445        ESTABLISHED
> tcp        0      0 10.0.2.15:55676         192.168.2.88:445        ESTABLISHED
> tcp        0      0 10.0.2.15:55720         192.168.2.88:445        ESTABLISHED
> tcp        0      1 10.0.2.15:55770         192.168.2.88:445        SYN_SENT
> tcp        1      0 10.0.2.15:55820         192.168.2.88:445        CLOSE_WAIT
> tcp        0      1 10.0.2.15:55868         192.168.2.88:445        SYN_SENT
> tcp        0      0 10.0.2.15:55912         192.168.2.88:445        ESTABLISHED
> tcp        0      0 10.0.2.15:55962         192.168.2.88:445        ESTABLISHED
> tcp        1      0 10.0.2.15:56010         192.168.2.88:445        CLOSE_WAIT
> tcp        0      1 10.0.2.15:56058         192.168.2.88:445        SYN_SENT
> tcp        0      0 10.0.2.15:56056         192.168.2.88:445        LAST_ACK
> tcp        0      0 10.0.2.15:56104         192.168.2.88:445        ESTABLISHED
> tcp        0      0 10.0.2.15:56162         192.168.2.88:445        ESTABLISHED
> tcp        0      0 10.0.2.15:56202         192.168.2.88:445        ESTABLISHED
> tcp        0      1 10.0.2.15:56246         192.168.2.88:445        SYN_SENT
> tcp        0      0 10.0.2.15:56290         192.168.2.88:445        ESTABLISHED
> ....etc.
> 
> Rebooting in 4.0.8 makes the issue go away, and I can have the shares mounted
> as long as I want without a connection flood. Hence I assume that it's a
> smbclient + Kernel 4.0.9 issue

smbclient is a command-line tool, if you're just mounting CIFS shares then this
is an issue in the kernel rather than in smbclient.

Jelmer