scp fails to copy files from sysfs

[Alfonso Sanchez-Beato]

When I try to copy some files from sysfs directly using scp it fails. This can be reproduced locally with:

ubuntu@ubuntu:~$ scp ubuntu@localhost:/sys/firmware/efi/efivars/BootOrder-8be4df61-93ca-11d2-aa0d-00e098032b8c .
ubuntu@localhost's password:
BootOrder-8be4df61-93ca-11d2-aa0d-00e098032b8c 0% 0 0.0KB/s --:-- ETA
scp: read remote "/sys/firmware/efi/efivars/BootOrder-8be4df61-93ca-11d2-aa0d-00e098032b8c" : Failure

The file is readable:

ubuntu@ubuntu:~$ od -b /sys/firmware/efi/efivars/BootOrder-8be4df61-93ca-11d2-aa0d-00e098032b8c
0000000 007 000 000 000 002 000 003 000 000 000 004 000
0000014

And I see this in the journal:

Jun 13 13:30:49 ubuntu sftp-server[5115]: error: process_read: seek "/sys/firmware/efi/efivars/BootOrder-8be4df61-93ca-11d2-aa0d-00e098032b8c": Illegal seek

This was working fine in 22.04. Interestingly, using a scp 22.04 client with a 24.04 kernel works fine.

[Mitchell Dzurick (mitchdz)]

Thank you for taking the time to make this bug Alfonso!

I can reproduce this in a noble-vm very easily.

$ lxc launch ubuntu:noble n-vm --vm
$ lxc shell n-vm
# rm /etc/ssh/sshd_config.d/60-cloudimg-settings.conf
# sed -i 's/#PermitRootLogin prohibit-password/PermitRootLogin yes/' /etc/ssh/sshd_config
# echo "root:pass" | chpasswd
# systemctl restart ssh
# scp root@localhost:/sys/firmware/efi/efivars/BootOrder-8be4df61-93ca-11d2-aa0d-00e098032b8c .

However it's not just every file in /sys/, there are some files you can still scp. For example:

# scp root@localhost:/sys/firmware/efi/runtime .

You can also cp the efi variable file and then scp it fine.
# cp /sys/firmware/efi/efivars/BootOrder-8be4df61-93ca-11d2-aa0d-00e098032b8c ./
# scp root@localhost:/root/BootOrder-8be4df61-93ca-11d2-aa0d-00e098032b8c ./

[Mitchell Dzurick (mitchdz)]

Just for fun, I also tried the latest openssh-client that we have in Jammy and see it works too -

# wget https://launchpad.net/ubuntu/+archive/primary/+files/openssh-client_8.9p1-3ubuntu0.7_amd64.deb
# dpkg -i ./openssh-client_8.9p1-3ubuntu0.7_amd64.deb
# scp root@localhost:/sys/firmware/efi/efivars/BootOrder-8be4df61-93ca-11d2-aa0d-00e098032b8c .
root@localhost's password:
BootOrder-8be4df61-93ca-11d2-aa0d-00e098032b8c 100% 20 27.4KB/s 00:00

[Mitchell Dzurick (mitchdz)]

To be complete, I also tried openssh-server_9.3p1-1ubuntu3.3 and see this issue on noble.

Which leaves something changed between openssh-client 8.9 and 9.3 to cause this behavior.