net/sched: sch_cake: Fix incorrect qlen reduction in cake_drop

Summary

In the Linux kernel, the following vulnerability has been resolved: net/sched: sch_cake: Fix incorrect qlen reduction in cake_drop In cake_drop(), qdisc_tree_reduce_backlog() is used to update the qlen and backlog of the qdisc hierarchy. Its caller, cake_enqueue(), assumes that the parent qdisc will enqueue the current packet. However, this assumption breaks when cake_enqueue() returns NET_XMIT_CN: the parent qdisc stops enqueuing current packet, leaving the tree qlen/backlog accounting inconsistent. This mismatch can lead to a NULL dereference (e.g., when the parent Qdisc is qfq_qdisc). This patch computes the qlen/backlog delta in a more robust way by observing the difference before and after the series of cake_drop() calls, and then compensates the qdisc tree accounting if cake_enqueue() returns NET_XMIT_CN. To ensure correct compensation when ACK thinning is enabled, a new variable is introduced to keep qlen unchanged.

Timeline

1. Dec 18, 2025, 3:02 PM UTCCVE published
2. May 23, 2026, 4:02 PM UTCRecord last updated

Affected versions

• Linux Linux

  From 5.10.241 · fixed in 5.10.248; From 5.15.190 · fixed in 5.15.198; From 6.1.149 · fixed in 6.1.160; From 6.6.103 · fixed in 6.6.120; From 6.12.44 · fixed in 6.12.63; From 5.4.297 · fixed in 5.5; From 6.16.4 · fixed in 6.17

• Linux Linux

  6.17

References 9