CVE-2025-37953 - Linux Kernel sch HTB NULL Pointer Dereference Vulnerability

CVE-2025-37953 - Linux Kernel sch HTB NULL Pointer Dereference Vulnerability

https://cvefeed.io/rssfeed/latest.atom / Tue, 05/20/2025 - 20:41
CVE ID : CVE-2025-37953
Published : May 20, 2025, 4:15 p.m. | 54 minutes ago
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.
Severity: 0.0 | NA
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