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Re: Strange ssh hangups, netbsd-9 GENERIC

On 3/12/21 8:38 AM, RVP wrote:
On Fri, 12 Mar 2021, Louis Guillaume wrote:

OpenSSH_8.0 NetBSD_Secure_Shell-20190418-hpn13v14-lpk, OpenSSL 1.1.1g 21 Apr 2020

Is this the server or the client? Can you post both?

ssh -vvv user%ser.ver@localhost 'dd if=/dev/zero bs=1m count=1 2>/dev/null' >out.bin 2>ssh.log.txt

Actually out.bin is 0b after running that - but it doesn't surprise me. Would it actually send text to stdout for each \0 returned by dd? Seems like it would basically be an empty string. The stderr is below. Thanks for looking!

You should get a 1MB file if /dev/zero exists, and is readable on
the server (and the dd on the server understands `bs=1m'):

$ ssh -vvv u%s.loc@localhost 'dd if=/dev/zero bs=1048576 count=1 2>/dev/null' >out.bin 2>ssh.log.txt
$ ls -l
total 1036
-rw-------  1 rvp  wheel  1048576 Mar 12 13:15 out.bin
-rw-------  1 rvp  wheel    11282 Mar 12 13:15 ssh.log.txt
$ hexdump -C out.bin
00000000  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00 |................|

Yes - it's not writing any data through the socket after some non-specific number of bytes. So the output of this is just empty.

OpenSSH_8.1p1, LibreSSL 2.7.3

What OS & client is this? Can you try a different client?

Connecting from NetBSD or macOS hosts gives the results I've been describing. But a connection from Linux is never accepted. We get this in the authlog:

ssh_dispatch_run_fatal: Connection from port 35632: Network is unreachable [preauth]

debug1: Exit status -1

The client is not exiting cleanly. It should--even if there
is a command execution error on the server.


It's definitely something on the server. When this hangup happens I see this in the authlog...

sshd[15352]: fatal: process_output: ssh_packet_write_poll: Network is unreachable

... but the system is consistently up and transferring data with no downtime (it is in fact a firewall). The problem seems isolated to sshd, and only when a rush of data happens.

Here's the interface in case that helps.

        address: 02:00:e8:16:41:15
        media: Ethernet autoselect (1000baseT full-duplex)
        status: active
        inet broadcast flags 0x0
        inet6 fe80::e8ff:fe16:4115%wm1/64 flags 0x0 scopeid 0x2


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