Overview
About vulnerability
In the Linux kernel, the following vulnerability has been resolved:
net/sched: Make cake_enqueue return NET_XMIT_CN when past buffer_limit
The following setup can trigger a WARNING in htb_activate due to the condition: !cl->leaf.q->q.qlen
tc qdisc del dev lo root
tc qdisc add dev lo root handle 1: htb default 1
tc class add dev lo parent 1: classid 1:1
htb rate 64bit
tc qdisc add dev lo parent 1:1 handle f:
cake memlimit 1b
ping -I lo -f -c1 -s64 -W0.001 127.0.0.1
This is because the low memlimit leads to a low buffer_limit, which causes packet dropping. However, cake_enqueue still returns NET_XMIT_SUCCESS, causing htb_enqueue to call htb_activate with an empty child qdisc. We should return NET_XMIT_CN when packets are dropped from the same tin and flow.
I do not believe return value of NET_XMIT_CN is necessary for packet drops in the case of ack filtering, as that is meant to optimize performance, not to signal congestion.
Details
- Affected product:
- AlmaLinux 9.2 ESU , Oracle Linux 7 ELS , TuxCare 9.6 ESU , Ubuntu 20.04 ELS
- Affected packages:
- kernel-uek @ 5.4.17 (+3 more)
In the Linux kernel, the following vulnerability has been resolved:
net/sched: Make cake_enqueue return NET_XMIT_CN when past buffer_limit
The following setup can trigger a WARNING in htb_activate due to the condition: !cl->leaf.q->q.qlen
tc qdisc del dev lo root
tc qdisc add dev lo root handle 1: htb default 1
tc class add dev lo parent 1: classid 1:1
htb rate 64bit
tc qdisc add dev lo parent 1:1 handle f:
cake memlimit 1b
ping -I lo -f -c1 -s64 -W0.001 127.0.0.1
This is because the low memlimit leads to a low buffer_limit, which causes packet dropping. However, cake_enqueue still returns NET_XMIT_SUCCESS, causing htb_enqueue to call htb_activate with an empty child qdisc. We should return NET_XMIT_CN when packets are dropped from the same tin and flow.
I do not believe return value of NET_XMIT_CN is necessary for packet drops in the case of ack filtering, as that is meant to optimize performance, not to signal congestion.