SSH pipe not closed when receiving side closes

[ghewson]

The command

ssh root@openwrt "tcpdump -i lan0 -U -w -" | wireshark -k -i -

as described here:

https://openwrt.org/docs/guide-user/firewall/misc/tcpdump_wireshark

allows viewing of network traffic on the OpenWrt host from another host. The command works, but when Wireshark is closed the pipe stalls and the tcpdump command must be killed manually.

This is using OpenWrt 24.10.2 with Dropbear server v2024.86 and an OpenSSH client.

A minimal test case is:

ssh user@host "cat /dev/zero" |false

as described here:

https://unix.stackexchange.com/questions/161690/terminating-ssh-called-from-a-script-sigpipe-handling

The command hangs when connecting to OpenWrt running Dropbear, but terminates normally when connecting to a server running OpenSSH.

I've also reproduced the problem by running the test case against an Ubuntu machine which has the dropbear package installed, running Dropbear server version 2022.83-4. Again, if OpenSSH server version 9.9 is installed instead, the test command terminates normally.

[SOwOphie]

I'm using Dropbear v2025.88 for my Git server, and recently a Protocol error started appearing at the end of every push. From what I can tell, this error is purely cosmetic, and the integrity of the transfer is not affected. My guess is that this is the same problem...?

Enumerating objects: 9, done.
Counting objects: 100% (9/9), done.
Delta compression using up to 24 threads
Compressing objects: 100% (5/5), done.
Writing objects: 100% (5/5), 865 bytes | 865.00 KiB/s, done.
Total 5 (delta 4), reused 0 (delta 0), pack-reused 0 (from 0)
remote: Error: Protocol error
To sowophie.io:priv/todo
   fd83941..39c5475  main -> main

The push was done using OpenSSH_10.0p2, OpenSSL 3.4.2 1 Jul 2025, and git version 2.49.1, both on the client and the server. Unfortunately my update process is a bit wonky and I cannot retroactively tell exactly what changed.

Edit: please disregard, that turned out to be an unrelated issue ._.