net_sched: sch_sfq: fix a potential crash on gso_skb handling

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: net_sched: sch_sfq: fix a potential crash on gso_skb handling SFQ has an assumption of always being able to queue at least one packet. However, after the blamed commit, sch->q.len can be inflated by packets in sch->gso_skb, and an enqueue() on an empty SFQ qdisc can be followed by an immediate drop. Fix sfq_drop() to properly clear q->tail in this situation. ip netns add lb ip link add dev to-lb type veth peer name in-lb netns lb ethtool -K to-lb tso off # force qdisc to requeue gso_skb ip netns exec lb ethtool -K in-lb gro on # enable NAPI ip link set dev to-lb up ip -netns lb link set dev in-lb up ip addr add dev to-lb 192.168.20.1/24 ip -netns lb addr add dev in-lb 192.168.20.2/24 tc qdisc replace dev to-lb root sfq limit 100 ip netns exec lb netserver netperf -H 192.168.20.2 -l 100 & netperf -H 192.168.20.2 -l 100 & netperf -H 192.168.20.2 -l 100 & netperf -H 192.168.20.2 -l 100 &

References

• https://git.kernel.org/stable/c/c337efb20d6d9f9bbb4746f6b119917af5c886dc
• https://git.kernel.org/stable/c/b44f791f27b14c9eb6b907fbe51f2ba8bec32085
• https://git.kernel.org/stable/c/5814a7fc3abb41f63f2d44c9d3ff9d4e62965b72
• https://git.kernel.org/stable/c/9c19498bdd7cb9d854bd3c54260f71cf7408495e
• https://git.kernel.org/stable/c/b4e9bab6011b9559b7c157b16b91ae46d4d8c533
• https://git.kernel.org/stable/c/d1bc80da75c789f2f6830df89d91fb2f7a509943
• https://git.kernel.org/stable/c/82448d4dcd8406dec688632a405fdcf7f170ec69
• https://git.kernel.org/stable/c/82ffbe7776d0ac084031f114167712269bf3d832