net/sched: cls_u32: fix manual hash table handle IDR aliasing

Summary

In the Linux kernel, the following vulnerability has been resolved: net/sched: cls_u32: fix manual hash table handle IDR aliasing A u32 hash table created with an explicit handle ('tc filter add ... handle 801: u32 divisor N') keys its IDR entry on the raw handle, while the destroy paths free it under handle2id(handle). The two key domains disagree for handles in the 0x800..0xFFF htid range: handle2id() folds them back into the auto-allocated id space (1..0x7FF). A manual table therefore leaves its raw-keyed IDR entry unreachable on delete (a permanent leak), and its delete can drop the idr entry of an unrelated live auto table. A later auto allocation can then hand out a handle that aliases the live manual table; u32_lookup_ht() first-match routes lookups and TCA_U32_LINK for that htid to the wrong table. Key the divisor-path alloc on handle2id(handle) so allocation and removal share one key domain. A manual handle that maps onto an id already in use is rejected with -ENOSPC, and auto allocation skips ids held by live manual tables. Conditions to recreate: ip link add test0 type dummy tc qdisc add dev test0 clsact tc filter add dev test0 ingress protocol ip pref 1 \ handle 801: u32 divisor 16 tc filter add dev test0 ingress protocol ip pref 2 u32 divisor 16 tc -d filter show dev test0 ingress | grep 'fh 801:' unpatched: two live tables with handle 0x80100000 (the pref 2 root hnode is auto-allocated id 1); patched: the auto hnode takes id 2. Also tested with a poc with a live u32 table on the block, add/delete a manual table 'handle 901: u32 divisor 1' twice; unpatched, the re-add fails with -ENOSPC because the raw key leaked on the first delete.

Timeline

1. Oct 18, 2026, 3:19 PM UTCCVE published
2. Oct 19, 2026, 9:22 AM UTCRecord last updated

Affected versions

• Linux Linux

  From 9b2c3184e126b941dfa716b8128ed6db92a64e2f · fixed in 21fc07924e996e1e661268ca269c86b8d59d25b3; From 789f9963bd031c3a185605665b744912df8e7eda · fixed in 0fac292d93fdb313099e98cce928b3a524c92c94; From 73af53d82076bbe184d9ece9e14b0dc8599e6055 · fixed in 54a454c5e41f5e2cb70c8163140ce095c5d5eefd; From 73af53d82076bbe184d9ece9e14b0dc8599e6055 · fixed in f6696481eedfd5752b4b56eed715d0b0fe48b9c5; From 73af53d82076bbe184d9ece9e14b0dc8599e6055 · fixed in 2f898f9ec7c73c5697ee462681e7ea6984ee1f3d; From 73af53d82076bbe184d9ece9e14b0dc8599e6055 · fixed in 0a5f5d9e94dead312d32c366b917c64e552b72f7; From 6.1.119 · fixed in 6.1.189; From 6.6.63 · fixed in 6.6.158; From 6.11.10 · fixed in 6.12

• Linux Linux

  6.12

• KernelLinux

  fixed in 6.1.189; From 6.2.0 · fixed in 6.6.158; From 6.7.0 · fixed in 6.12.112; From 6.12.0 · fixed in 6.18.55; From 6.13.0 · fixed in 7.2.9

References 6