{"id":"DEBIAN-CVE-2025-38468","details":"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 -\u003e htb_deactivate -\u003e    htb_deactiviate_prios -\u003e htb_remove_class_from_row -\u003e 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/","modified":"2026-09-01T16:05:48.175953754Z","published":"2025-07-28T12:15:28.503Z","upstream":["CVE-2025-38468"],"references":[{"type":"ADVISORY","url":"https://security-tracker.debian.org/tracker/CVE-2025-38468"}],"affected":[{"package":{"name":"linux","ecosystem":"Debian:12","purl":"pkg:deb/debian/linux?arch=source&distro=bookworm"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"6.1.147-1"}]}],"versions":["6.1.106-1","6.1.106-2","6.1.106-3","6.1.112-1","6.1.115-1","6.1.119-1","6.1.123-1","6.1.124-1","6.1.128-1","6.1.129-1","6.1.133-1","6.1.135-1","6.1.137-1","6.1.139-1","6.1.140-1","6.1.27-1","6.1.37-1","6.1.38-1","6.1.38-2","6.1.38-2~bpo11+1","6.1.38-3","6.1.38-4","6.1.38-4~bpo11+1","6.1.52-1","6.1.55-1","6.1.55-1~bpo11+1","6.1.64-1","6.1.66-1","6.1.67-1","6.1.69-1","6.1.69-1~bpo11+1","6.1.76-1","6.1.76-1~bpo11+1","6.1.82-1","6.1.85-1","6.1.90-1","6.1.90-1~bpo11+1","6.1.94-1","6.1.94-1~bpo11+1","6.1.98-1","6.1.99-1"],"ecosystem_specific":{"urgency":"not yet assigned"},"database_specific":{"source":"https://storage.googleapis.com/osv-test-debian-osv/debian-cve-osv/DEBIAN-CVE-2025-38468.json"}},{"package":{"name":"linux","ecosystem":"Debian:13","purl":"pkg:deb/debian/linux?arch=source&distro=trixie"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"6.12.41-1"}]}],"versions":["6.12.38-1"],"ecosystem_specific":{"urgency":"not yet assigned"},"database_specific":{"source":"https://storage.googleapis.com/osv-test-debian-osv/debian-cve-osv/DEBIAN-CVE-2025-38468.json"}},{"package":{"name":"linux","ecosystem":"Debian:14","purl":"pkg:deb/debian/linux?arch=source&distro=forky"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"6.16.3-1"}]}],"versions":["6.12.100-1","6.12.101-1","6.12.105-1","6.12.107-1","6.12.38-1","6.12.41-1","6.12.43-1","6.12.43-1~bpo12+1","6.12.48-1","6.12.57-1","6.12.57-1~bpo12+1","6.12.63-1","6.12.63-1~bpo12+1","6.12.69-1","6.12.69-1~bpo12+1","6.12.73-1","6.12.73-1~bpo12+1","6.12.74-1","6.12.74-2","6.12.74-2~bpo12+1","6.12.85-1","6.12.85-1~bpo12+1","6.12.86-1","6.12.86-1~bpo12+1","6.12.88-1","6.12.88-1~bpo12+1","6.12.90-1","6.12.90-1~bpo12+1","6.12.90-2","6.12.90-2~bpo12+1","6.12.94-1","6.12.94-1~bpo12+1","6.12.95-1","6.12.95-1~bpo12+1","6.12.96-1","6.13.10-1~exp1","6.13.11-1~exp1","6.13.2-1~exp1","6.13.3-1~exp1","6.13.4-1~exp1","6.13.5-1~exp1","6.13.6-1~exp1","6.13.7-1~exp1","6.13.8-1~exp1","6.13.9-1~exp1","6.13~rc6-1~exp1","6.13~rc7-1~exp1","6.14.3-1~exp1","6.14.5-1~exp1","6.14.6-1~exp1","6.15-1~exp1","6.15.1-1~exp1","6.15.2-1~exp1","6.15.3-1~exp1","6.15.4-1~exp1","6.15.5-1~exp1","6.15.6-1~exp1","6.15~rc7-1~exp1","6.16-1~exp1","6.16.1-1~exp1","6.16.3-1~bpo13+1","6.16~rc7-1~exp1"],"ecosystem_specific":{"urgency":"not yet assigned"},"database_specific":{"source":"https://storage.googleapis.com/osv-test-debian-osv/debian-cve-osv/DEBIAN-CVE-2025-38468.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H"}]}