Description
In the Linux kernel, the following vulnerability has been resolved: sch_htb: make htb_deactivate() idempotent Alan reported a NULL pointer dereference in htb_next_rb_node() after we made htb_qlen_notify() idempotent. It turns out in the following case it introduced some regression: htb_dequeue_tree(): |-> fq_codel_dequeue() |-> qdisc_tree_reduce_backlog() |-> htb_qlen_notify() |-> htb_deactivate() |-> htb_next_rb_node() |-> htb_deactivate() For htb_next_rb_node(), after calling the 1st htb_deactivate(), the clprio[prio]->ptr could be already set to NULL, which means htb_next_rb_node() is vulnerable here. For htb_deactivate(), although we checked qlen before calling it, in case of qlen==0 after qdisc_tree_reduce_backlog(), we may call it again which triggers the warning inside. To fix the issues here, we need to: 1) Make htb_deactivate() idempotent, that is, simply return if we already call it before. 2) Make htb_next_rb_node() safe against ptr==NULL. Many thanks to Alan for testing and for the reproducer.
Product status
e6b45f4de763b00dc1c55e685e2dd1aaf525d3c1 (git) before 99ff8a20fd61315bf9ae627440a5ff07d22ee153
32ae12ce6a9f6bace186ca7335220ff59b6cc3cd (git) before a9945f7cf1709adc5d2d31cb6cfc85627ce299a8
967955c9e57f8eebfccc298037d4aaf3d42bc1c9 (git) before c2d25fddd867ce20a266806634eeeb5c30cb520c
73cf6af13153d62f9b76eff422eea79dbc70f15e (git) before c928dd4f6bf0c25c72b11824a1e9ac9bd37296a0
bbbf5e0f87078b715e7a665d662a2c0e77f044ae (git) before 31ff70ad39485698cf779f2078132d80b57f6c07
0a188c0e197383683fd093ab1ea6ce9a5869a6ea (git) before 98cd7ed92753090a714f0802d4434314526fe61d
a61f1b5921761fbaf166231418bc1db301e5bf59 (git) before c4792b9e38d2f61b07eac72f10909fa76130314b
5ba8b837b522d7051ef81bacf3d95383ff8edce5 (git) before 3769478610135e82b262640252d90f6efb05be71
6.1.138 (semver) before 6.1.139
6.6.90 (semver) before 6.6.91
6.12.28 (semver) before 6.12.29
6.14.6 (semver) before 6.14.7
References
lists.debian.org/debian-lts-announce/2025/08/msg00010.html
git.kernel.org/...c/99ff8a20fd61315bf9ae627440a5ff07d22ee153
git.kernel.org/...c/a9945f7cf1709adc5d2d31cb6cfc85627ce299a8
git.kernel.org/...c/c2d25fddd867ce20a266806634eeeb5c30cb520c
git.kernel.org/...c/c928dd4f6bf0c25c72b11824a1e9ac9bd37296a0
git.kernel.org/...c/31ff70ad39485698cf779f2078132d80b57f6c07
git.kernel.org/...c/98cd7ed92753090a714f0802d4434314526fe61d
git.kernel.org/...c/c4792b9e38d2f61b07eac72f10909fa76130314b
git.kernel.org/...c/3769478610135e82b262640252d90f6efb05be71