Odhcp6c logspamming via netifd: cat: write error: Broken pipe

Netgear R7800, running 22.03.4 but this started several maintenance releases ago, possibly even with the 21.x series.

The system log is spammed with:

Sat Apr 15 17:15:35 2023 daemon.notice netifd: wan6 (1650): cat: write error: Broken pipe

repeating roughly every 90-120 seconds.

My ISP provides both an address and a delegated /60 to wan6; in /etc/config/network:

config interface 'wan6'
	option proto 'dhcpv6'
	option reqaddress 'try'
	option reqprefix '60'
	option device 'eth0.2'

Prefix delegation seems to work correctly: I have several LANs each with a different /64 subnet of my ISP-delegated /60 getting allocated correctly, devices getting these addresses and IPv6 traffic from the client devices works.

pid 1650 is indeed the odhcp6c process for wan6:

 1650 root       884 S    odhcp6c -s /lib/netifd/dhcpv6.script -Ntry -P60 -t120 eth0.2

Any idea where this error is coming from?

Could be from within /lib/netifd/dhcpv6.script or any user scripts called from within (/etc/odhcp6c.user, /etc/odhcp6c.user.d/*).

The only cat in the main script is cat /proc/sys/net/ipv6/conf/$device/hop_limit, so try running cat /proc/sys/net/ipv6/conf/eth0.2/hop_limit manually over SSH and see if it gives that message,

Seems to be fine:

# cat /proc/sys/net/ipv6/conf/eth0.2/hop_limit

The other two locations don't seem to have anything relevant: /etc/odhcp6c.user is empty (other than the comment/description on the first line), and there's nothing in /etc/odhcp6c.user.d/.

Sorry for necroposting but I am getting the same thing with the same results (64) when running

cat /proc/sys/net/ipv6/conf/{any device here}/hop_limit