sch_htb: make htb_deactivate() idempotent

Summary

In the Linux kernel, the following vulnerability has been resolved: sch_htb: make htb_deactivate() idempotent Alan reported a NULL pointer dereference in htb_next_rb_node() after we made htb_qlen_notify() idempotent. It turns out in the following case it introduced some regression: htb_dequeue_tree(): |-> fq_codel_dequeue() |-> qdisc_tree_reduce_backlog() |-> htb_qlen_notify() |-> htb_deactivate() |-> htb_next_rb_node() |-> htb_deactivate() For htb_next_rb_node(), after calling the 1st htb_deactivate(), the clprio[prio]->ptr could be already set to NULL, which means htb_next_rb_node() is vulnerable here. For htb_deactivate(), although we checked qlen before calling it, in case of qlen==0 after qdisc_tree_reduce_backlog(), we may call it again which triggers the warning inside. To fix the issues here, we need to: 1) Make htb_deactivate() idempotent, that is, simply return if we already call it before. 2) Make htb_next_rb_node() safe against ptr==NULL. Many thanks to Alan for testing and for the reproducer.

Timeline

1. May 20, 2025, 4:01 PM UTCCVE published
2. May 11, 2026, 9:18 PM UTCRecord last updated

Affected versions

• Linux Linux

  Version range not reported

• Linux Linux

  From 6.1.138 · fixed in 6.1.139; From 6.6.90 · fixed in 6.6.91; From 6.12.28 · fixed in 6.12.29; From 6.14.6 · fixed in 6.14.7

References 8