https://vulnerability.circl.lu Contains only the most 10 recent entries. http://www.rssboard.org/rss-specification python-feedgen en Tue, 29 Sep 2026 20:53:13 +0000 https://vulnerability.circl.lu/vuln/cve-2026-63918 <p><strong>Affected:</strong> Linux</p> <p>In the Linux kernel, the following vulnerability has been resolved:</p> <p>l2tp: use refcount_inc_not_zero in l2tp_session_get_by_ifname</p> <p>A reader in l2tp_session_get_by_ifname() can return a pointer to a session whose refcount has reached zero. The getter takes its reference with plain refcount_inc(), but every other session getter in the same file (l2tp_v2_session_get, l2tp_v3_session_get, and the corresponding _get_next variants) uses refcount_inc_not_zero() because the IDR/RCU lookup can race with refcount_dec_and_test() -&gt; l2tp_session_free() -&gt; kfree_rcu(). The ifname getter is the only outlier; the inconsistency was raised on-list after 979c017803c4 (&#34;l2tp: use list_del_rcu in l2tp_session_unhash&#34;).</p> <p>A reader inside rcu_read_lock_bh() that matches session-&gt;ifname can be preempted between the strcmp() and the refcount_inc(). If the last reference drops on another CPU in that window, the reader&#39;s refcount_inc() runs on a counter that has reached zero. refcount_t catches the addition-on-zero, prints &#34;refcount_t: addition on 0; use-after-free&#34;, saturates the counter, and returns the saturated pointer to the caller. Session memory is held live by the in-flight RCU read section, but the kfree_rcu() callback queued from l2tp_session_free() will free it once the grace period closes; a caller that dereferences the returned session past that point hits a slab-use-after-free. On PREEMPT_RT local_bh_disable() is a per-CPU sleeping lock and the preemption window is real; on stock PREEMP…</p> <p><strong>Affected:</strong> Linux</p> <p>In the Linux kernel, the following vulnerability has been resolved:</p> <p>l2tp: use refcount_inc_not_zero in l2tp_session_get_by_ifname</p> <p>A reader in l2tp_session_get_by_ifname() can return a pointer to a session whose refcount has reached zero. The getter takes its reference with plain refcount_inc(), but every other session getter in the same file (l2tp_v2_session_get, l2tp_v3_session_get, and the corresponding _get_next variants) uses refcount_inc_not_zero() because the IDR/RCU lookup can race with refcount_dec_and_test() -&gt; l2tp_session_free() -&gt; kfree_rcu(). The ifname getter is the only outlier; the inconsistency was raised on-list after 979c017803c4 (&#34;l2tp: use list_del_rcu in l2tp_session_unhash&#34;).</p> <p>A reader inside rcu_read_lock_bh() that matches session-&gt;ifname can be preempted between the strcmp() and the refcount_inc(). If the last reference drops on another CPU in that window, the reader&#39;s refcount_inc() runs on a counter that has reached zero. refcount_t catches the addition-on-zero, prints &#34;refcount_t: addition on 0; use-after-free&#34;, saturates the counter, and returns the saturated pointer to the caller. Session memory is held live by the in-flight RCU read section, but the kfree_rcu() callback queued from l2tp_session_free() will free it once the grace period closes; a caller that dereferences the returned session past that point hits a slab-use-after-free. On PREEMPT_RT local_bh_disable() is a per-CPU sleeping lock and the preemption window is real; on stock PREEMP…</p> https://vulnerability.circl.lu/vuln/cve-2026-63918