In the Linux kernel, the following vulnerability has been resolved: net/sched: sch_api: fix xa_insert() error path in tcf_block_get_ext() This command: $ tc qdisc replace dev eth0 ingress_block 1 egress_block 1 clsact Error: block dev insert failed: -EBUSY. fails because user space requests the same block index to be set for both ingress and egress. [ side note, I don't think it even failed prior to commit 913b47d3424e ("net/sched: Introduce tc block netdev tracking infra"), because this is a command from an old set of notes of mine which used to work, but alas, I did not scientifically bisect this ] The problem is not that it fails, but rather, that the second time around, it fails differently (and irrecoverably): $ tc qdisc replace dev eth0 ingress_block 1 egress_block 1 clsact Error: dsa_core: Flow block cb is busy. [ another note: the extack is added by me for illustration purposes. the context of the problem is that clsact_init() obtains the same &q->ingress_blo…