CVE-2025-38468
published 2025-07-28CVE-2025-38468: In the Linux kernel, the following vulnerability has been resolved: net/sched: Return NULL when htb_lookup_leaf encounters an empty rbtree htb_lookup_leaf has…
medium5.5CVSS 3.1
AVLACLPRLUINSUCNINAH
In the Linux kernel, the following vulnerability has been resolved:
net/sched: Return NULL when htb_lookup_leaf encounters an empty rbtree
htb_lookup_leaf has a BUG_ON that can trigger with the following:
tc qdisc del dev lo root
tc qdisc add dev lo root handle 1: htb default 1
tc class add dev lo parent 1: classid 1:1 htb rate 64bit
tc qdisc add dev lo parent 1:1 handle 2: netem
tc qdisc add dev lo parent 2:1 handle 3: blackhole
ping -I lo -c1 -W0.001 127.0.0.1
The root cause is the following:
1. htb_dequeue calls htb_dequeue_tree which calls the dequeue handler on
the selected leaf qdisc
2. netem_dequeue calls enqueue on the child qdisc
3. blackhole_enqueue drops the packet and returns a value that is not
just NET_XMIT_SUCCESS
4. Because of this, netem_dequeue calls qdisc_tree_reduce_backlog, and
since qlen is now 0, it calls htb_qlen_notify -> htb_deactivate ->
htb_deactiviate_prios -> htb_remove_class_from_row -> htb_safe_rb_erase
5. As this is the only class in the selected hprio rbtree,
__rb_change_child in __rb_erase_augmented sets the rb_root pointer to
NULL
6. Because blackhole_dequeue returns NULL, netem_dequeue returns NULL,
which causes htb_dequeue_tree to call htb_lookup_leaf with the same
hprio rbtree, and fail the BUG_ON
The function graph for this scenario is shown here:
0) | htb_enqueue() {
0) + 13.635 us | netem_enqueue();
0) 4.719 us | htb_activate_prios();
0) # 2249.199 us | }
0) | htb_dequeue() {
0) 2.355 us | htb_lookup_leaf();
0) | netem_dequeue() {
0) + 11.061 us | blackhole_enqueue();
0) | qdisc_tree_reduce_backlog() {
0) | qdisc_lookup_rcu() {
0) 1.873 us | qdisc_match_from_root();
0) 6.292 us | }
0) 1.894 us | htb_search();
0) | htb_qlen_notify() {
0) 2.655 us | htb_deactivate_prios();
0) 6.933 us | }
0) + 25.227 us | }
0) 1.983 us | blackhole_dequeue();
0) + 86.553 us | }
0) # 2932.761 us | qdisc_warn_nonwc();
0) | htb_lookup_leaf() {
0) | BUG_ON();
The full original bug report can be seen here [1].
We can fix this just by returni
Affected
38 ranges· showing 25
| Vendor | Product | Version range | Fixed in |
|---|---|---|---|
| debian | debian_linux | — | — |
| debian | linux | < linux 6.1.147-1 (bookworm) | linux 6.1.147-1 (bookworm) |
| debian | linux-6.1 | < linux 6.1.147-1 (bookworm) | linux 6.1.147-1 (bookworm) |
| linux | linux | — | — |
| linux | linux | >= 512bb43eb5422ee69a1be05ea0d89dc074fac9a2 < fed3570e548a6c9f95c5f4c9e1a7afc1679fd90d | fed3570e548a6c9f95c5f4c9e1a7afc1679fd90d |
| linux | linux | >= 512bb43eb5422ee69a1be05ea0d89dc074fac9a2 < 5c0506cd1b1a3b145bda2612bbf7fe78d186c355 | 5c0506cd1b1a3b145bda2612bbf7fe78d186c355 |
| linux | linux | >= 512bb43eb5422ee69a1be05ea0d89dc074fac9a2 < 850226aef8d28a00cf966ef26d2f8f2bff344535 | 850226aef8d28a00cf966ef26d2f8f2bff344535 |
| linux | linux | >= 512bb43eb5422ee69a1be05ea0d89dc074fac9a2 < 890a5d423ef0a7bd13447ceaffad21189f557301 | 890a5d423ef0a7bd13447ceaffad21189f557301 |
| linux | linux | >= 512bb43eb5422ee69a1be05ea0d89dc074fac9a2 < 7ff2d83ecf2619060f30ecf9fad4f2a700fca344 | 7ff2d83ecf2619060f30ecf9fad4f2a700fca344 |
| linux | linux | >= 512bb43eb5422ee69a1be05ea0d89dc074fac9a2 < e5c480dc62a3025b8428d4818e722da30ad6804f | e5c480dc62a3025b8428d4818e722da30ad6804f |
| linux | linux | >= 512bb43eb5422ee69a1be05ea0d89dc074fac9a2 < 3691f84269a23f7edd263e9b6edbc27b7ae332f4 | 3691f84269a23f7edd263e9b6edbc27b7ae332f4 |
| linux | linux | >= 512bb43eb5422ee69a1be05ea0d89dc074fac9a2 < 0e1d5d9b5c5966e2e42e298670808590db5ed628 | 0e1d5d9b5c5966e2e42e298670808590db5ed628 |
| linux | linux_kernel | — | — |
| linux | linux_kernel | >= 0 < 5.10.244-1 | 5.10.244-1 |
| linux | linux_kernel | >= 0 < 6.1.147-1 | 6.1.147-1 |
| linux | linux_kernel | >= 0 < 6.12.41-1 | 6.12.41-1 |
| linux | linux_kernel | >= 0 < 6.16.3-1 | 6.16.3-1 |
| linux | linux_kernel | >= 0 < 5.15.0-163.173 | 5.15.0-163.173 |
| linux | linux_kernel | >= 0 < 6.8.0-100.100 | 6.8.0-100.100 |
| linux | linux_kernel | >= 2.6.29 < 5.4.297 | 5.4.297 |
| linux | linux_kernel | >= 5.11 < 5.15.190 | 5.15.190 |
| linux | linux_kernel | >= 5.16 < 6.1.147 | 6.1.147 |
| linux | linux_kernel | >= 5.5 < 5.10.241 | 5.10.241 |
| linux | linux_kernel | >= 6.13 < 6.15.8 | 6.15.8 |
| linux | linux_kernel | >= 6.2 < 6.6.100 | 6.6.100 |
CVSS provenance
nvdv3.15.5MEDIUMCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
osv5.5MEDIUM