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.
Affected products
Version statuses are supplied by the assigning organization. Consult the original record for detailed ranges and platform conditions.
Linux Linux
Default version status: unaffected
e6b45f4de763b00dc1c55e685e2dd1aaf525d3c1 to < 99ff8a20fd61315bf9ae627440a5ff07d22ee153affected32ae12ce6a9f6bace186ca7335220ff59b6cc3cd to < a9945f7cf1709adc5d2d31cb6cfc85627ce299a8affected967955c9e57f8eebfccc298037d4aaf3d42bc1c9 to < c2d25fddd867ce20a266806634eeeb5c30cb520caffected73cf6af13153d62f9b76eff422eea79dbc70f15e to < c928dd4f6bf0c25c72b11824a1e9ac9bd37296a0affectedbbbf5e0f87078b715e7a665d662a2c0e77f044ae to < 31ff70ad39485698cf779f2078132d80b57f6c07affected0a188c0e197383683fd093ab1ea6ce9a5869a6ea to < 98cd7ed92753090a714f0802d4434314526fe61daffecteda61f1b5921761fbaf166231418bc1db301e5bf59 to < c4792b9e38d2f61b07eac72f10909fa76130314baffected5ba8b837b522d7051ef81bacf3d95383ff8edce5 to < 3769478610135e82b262640252d90f6efb05be71affected
Linux Linux
Default version status: unaffected
6.1.138 to < 6.1.139affected6.6.90 to < 6.6.91affected6.12.28 to < 6.12.29affected6.14.6 to < 6.14.7affected
References
- https://git.kernel.org/stable/c/99ff8a20fd61315bf9ae627440a5ff07d22ee153 ↗
- https://git.kernel.org/stable/c/a9945f7cf1709adc5d2d31cb6cfc85627ce299a8 ↗
- https://git.kernel.org/stable/c/c2d25fddd867ce20a266806634eeeb5c30cb520c ↗
- https://git.kernel.org/stable/c/c928dd4f6bf0c25c72b11824a1e9ac9bd37296a0 ↗
- https://git.kernel.org/stable/c/31ff70ad39485698cf779f2078132d80b57f6c07 ↗
- https://git.kernel.org/stable/c/98cd7ed92753090a714f0802d4434314526fe61d ↗
- https://git.kernel.org/stable/c/c4792b9e38d2f61b07eac72f10909fa76130314b ↗
- https://git.kernel.org/stable/c/3769478610135e82b262640252d90f6efb05be71 ↗
- https://lists.debian.org/debian-lts-announce/2025/08/msg00010.html ↗