net/sched: Return NULL when htb_lookup_leaf encounters an empty rbtree

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2025-38468
StatePUBLISHED
AssignerLinux
Source PriorityCVE Program / NVD first with legacy fallback
Published2025-07-28 12:15:28 UTC
Updated2026-05-12 13:16:50 UTC
DescriptionIn 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 returning NULL instead of the BUG_ON, as htb_dequeue_tree returns NULL when htb_lookup_leaf returns NULL. [1] https://lore.kernel.org/netdev/pF5XOOIim0IuEfhI-SOxTgRvNoDwuux7UHKnE_Y5-zVd4wmGvNk2ceHjKb8ORnzw0cGwfmVu42g9dL7XyJLf1NEzaztboTWcm0Ogxuojoeo=@willsroot.io/

Risk And Classification

Primary CVSS: v3.1 5.5 MEDIUM from [email protected]

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

Problem Types: CWE-476

CVSS v3.1 Breakdown

Attack Vector
Local
Attack Complexity
Low
Privileges Required
Low
User Interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

NVD Known Affected Configurations (CPE 2.3)

TypeVendorProductVersionUpdateEditionLanguage
Operating System Linux Linux Kernel All All All All

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Linux Linux affected 512bb43eb5422ee69a1be05ea0d89dc074fac9a2 fed3570e548a6c9f95c5f4c9e1a7afc1679fd90d git Not specified
CNA Linux Linux affected 512bb43eb5422ee69a1be05ea0d89dc074fac9a2 5c0506cd1b1a3b145bda2612bbf7fe78d186c355 git Not specified
CNA Linux Linux affected 512bb43eb5422ee69a1be05ea0d89dc074fac9a2 850226aef8d28a00cf966ef26d2f8f2bff344535 git Not specified
CNA Linux Linux affected 512bb43eb5422ee69a1be05ea0d89dc074fac9a2 890a5d423ef0a7bd13447ceaffad21189f557301 git Not specified
CNA Linux Linux affected 512bb43eb5422ee69a1be05ea0d89dc074fac9a2 7ff2d83ecf2619060f30ecf9fad4f2a700fca344 git Not specified
CNA Linux Linux affected 512bb43eb5422ee69a1be05ea0d89dc074fac9a2 e5c480dc62a3025b8428d4818e722da30ad6804f git Not specified
CNA Linux Linux affected 512bb43eb5422ee69a1be05ea0d89dc074fac9a2 3691f84269a23f7edd263e9b6edbc27b7ae332f4 git Not specified
CNA Linux Linux affected 512bb43eb5422ee69a1be05ea0d89dc074fac9a2 0e1d5d9b5c5966e2e42e298670808590db5ed628 git Not specified
CNA Linux Linux affected 2.6.29 Not specified
CNA Linux Linux unaffected 2.6.29 semver Not specified
CNA Linux Linux unaffected 5.4.297 5.4.* semver Not specified
CNA Linux Linux unaffected 5.10.241 5.10.* semver Not specified
CNA Linux Linux unaffected 5.15.190 5.15.* semver Not specified
CNA Linux Linux unaffected 6.1.147 6.1.* semver Not specified
CNA Linux Linux unaffected 6.6.100 6.6.* semver Not specified
CNA Linux Linux unaffected 6.12.40 6.12.* semver Not specified
CNA Linux Linux unaffected 6.15.8 6.15.* semver Not specified
CNA Linux Linux unaffected 6.16 * original_commit_for_fix Not specified
ADP Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP affected V3.1.5 * custom Not specified
ADP Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP affected V3.1.5 * custom Not specified
ADP Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP affected V3.1.5 * custom Not specified
ADP Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP affected V3.1.5 * custom Not specified
ADP Siemens SIPLUS S7-1500 CPU 1518-4 PN/DP MFP affected V3.1.5 * custom Not specified

References

ReferenceSourceLinkTags
git.kernel.org/stable/c/3691f84269a23f7edd263e9b6edbc27b7ae332f4 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
lists.debian.org/debian-lts-announce/2025/10/msg00008.html af854a3a-2127-422b-91ae-364da2661108 lists.debian.org Third Party Advisory
cert-portal.siemens.com/productcert/html/ssa-082556.html 0b142b55-0307-4c5a-b3c9-f314f3fb7c5e cert-portal.siemens.com
git.kernel.org/stable/c/890a5d423ef0a7bd13447ceaffad21189f557301 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
git.kernel.org/stable/c/e5c480dc62a3025b8428d4818e722da30ad6804f 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
git.kernel.org/stable/c/fed3570e548a6c9f95c5f4c9e1a7afc1679fd90d 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
git.kernel.org/stable/c/0e1d5d9b5c5966e2e42e298670808590db5ed628 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
lists.debian.org/debian-lts-announce/2025/10/msg00007.html af854a3a-2127-422b-91ae-364da2661108 lists.debian.org Third Party Advisory
git.kernel.org/stable/c/850226aef8d28a00cf966ef26d2f8f2bff344535 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
git.kernel.org/stable/c/7ff2d83ecf2619060f30ecf9fad4f2a700fca344 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
git.kernel.org/stable/c/5c0506cd1b1a3b145bda2612bbf7fe78d186c355 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
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