CVE-2025-37797

In the Linux kernel, the following vulnerability has been resolved:<br /> <br /> net_sched: hfsc: Fix a UAF vulnerability in class handling<br /> <br /> This patch fixes a Use-After-Free vulnerability in the HFSC qdisc class<br /> handling. The issue occurs due to a time-of-check/time-of-use condition<br /> in hfsc_change_class() when working with certain child qdiscs like netem<br /> or codel.<br /> <br /> The vulnerability works as follows:<br /> 1. hfsc_change_class() checks if a class has packets (q.qlen != 0)<br /> 2. It then calls qdisc_peek_len(), which for certain qdiscs (e.g.,<br /> codel, netem) might drop packets and empty the queue<br /> 3. The code continues assuming the queue is still non-empty, adding<br /> the class to vttree<br /> 4. This breaks HFSC scheduler assumptions that only non-empty classes<br /> are in vttree<br /> 5. Later, when the class is destroyed, this can lead to a Use-After-Free<br /> <br /> The fix adds a second queue length check after qdisc_peek_len() to verify<br /> the queue wasn&amp;#39;t emptied.