CVE-2025-37953 (GCVE-0-2025-37953)

Vulnerability from cvelistv5 – Published: 2025-05-20 16:01 – Updated: 2026-05-11 21:18
VLAI
Title
sch_htb: make htb_deactivate() idempotent
Summary
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.
Severity
5.5 (Medium)
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
Assigner
References
Impacted products
Vendor Product Version
Linux Linux Affected: e6b45f4de763b00dc1c55e685e2dd1aaf525d3c1 , < 99ff8a20fd61315bf9ae627440a5ff07d22ee153 (git)
Affected: 32ae12ce6a9f6bace186ca7335220ff59b6cc3cd , < a9945f7cf1709adc5d2d31cb6cfc85627ce299a8 (git)
Affected: 967955c9e57f8eebfccc298037d4aaf3d42bc1c9 , < c2d25fddd867ce20a266806634eeeb5c30cb520c (git)
Affected: 73cf6af13153d62f9b76eff422eea79dbc70f15e , < c928dd4f6bf0c25c72b11824a1e9ac9bd37296a0 (git)
Affected: bbbf5e0f87078b715e7a665d662a2c0e77f044ae , < 31ff70ad39485698cf779f2078132d80b57f6c07 (git)
Affected: 0a188c0e197383683fd093ab1ea6ce9a5869a6ea , < 98cd7ed92753090a714f0802d4434314526fe61d (git)
Affected: a61f1b5921761fbaf166231418bc1db301e5bf59 , < c4792b9e38d2f61b07eac72f10909fa76130314b (git)
Affected: 5ba8b837b522d7051ef81bacf3d95383ff8edce5 , < 3769478610135e82b262640252d90f6efb05be71 (git)
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Linux Linux Affected: 6.1.138 , < 6.1.139 (semver)
Affected: 6.6.90 , < 6.6.91 (semver)
Affected: 6.12.28 , < 6.12.29 (semver)
Affected: 6.14.6 , < 6.14.7 (semver)
Create a notification for this product.
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Alan inform\u00f3 una desreferencia de puntero NULL en htb_next_rb_node() despu\u00e9s de que htb_qlen_notify() fuera idempotente. Resulta que en el siguiente caso introdujo alguna regresi\u00f3n: htb_dequeue_tree(): |-\u0026gt; fq_codel_dequeue() |-\u0026gt; qdisc_tree_reduce_backlog() |-\u0026gt; htb_qlen_notify() |-\u0026gt; htb_deactivate() |-\u0026gt; htb_next_rb_node() |-\u0026gt; htb_deactivate() Para htb_next_rb_node(), despu\u00e9s de llamar al primer htb_deactivate(), el clprio[prio]-\u0026gt;ptr podr\u00eda estar ya establecido en NULL, lo que significa que htb_next_rb_node() es vulnerable aqu\u00ed. Para htb_deactivate(), aunque verificamos qlen antes de llamarlo, en caso de qlen==0 despu\u00e9s de qdisc_tree_reduce_backlog(), podemos llamarlo nuevamente, lo que activa la advertencia interna. Para solucionar estos problemas, necesitamos: 1) Hacer que htb_deactivate() sea idempotente, es decir, que simplemente regrese si ya lo llamamos. 2) Hacer que htb_next_rb_node() sea seguro contra ptr==NULL. 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}


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