l2tp: use list_del_rcu in l2tp_session_unhash

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Summary

CVECVE-2026-64119
StatePUBLISHED
AssignerLinux
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-07-19 16:17:53 UTC
Updated2026-07-19 16:17:53 UTC
DescriptionIn the Linux kernel, the following vulnerability has been resolved: l2tp: use list_del_rcu in l2tp_session_unhash An unprivileged local user can pin a host CPU indefinitely in l2tp_session_get_by_ifname() by issuing L2TP_CMD_SESSION_GET on L2TP_ATTR_IFNAME concurrently with L2TP_CMD_SESSION_CREATE and L2TP_CMD_SESSION_DELETE on the same tunnel. All three commands take GENL_UNS_ADMIN_PERM, so CAP_NET_ADMIN in the netns user namespace suffices; on any host that has l2tp_core loaded the trigger is reachable from a standard `unshare -Urn` sandbox. l2tp_session_unhash() removes a session from tunnel->session_list with list_del_init(), but that list is walked by l2tp_session_get_by_ifname() with list_for_each_entry_rcu() under rcu_read_lock_bh(). list_del_init() leaves the deleted entry's next/prev self-pointing; a reader that has loaded the entry and then advances pos->list.next reads &session->list, container_of()s back to the same session, and list_for_each_entry_rcu() never reaches the list head. The CPU stays in strcmp() inside the walker, with BH and preemption disabled, so RCU grace periods on the host stall behind it and the wedged thread cannot be killed (SIGKILL is delivered on syscall return). Use list_del_rcu() to match the existing list_add_rcu() in l2tp_session_register(); the deleted session remains visible to in-flight walkers with consistent next/prev pointers until kfree_rcu() in l2tp_session_free() releases it. tunnel->session_list has exactly one list_del_init() call site; the list_del_init (&session->clist) at l2tp_core.c:533 operates on the per-collision list, which is not walked under RCU. list_empty(&session->list) is not used anywhere in net/l2tp/ after the unhash point, so dropping the post-delete self-init is safe; the fix has no userspace-visible behavior change.

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Linux Linux affected 89b768ec2dfefaeba5212de14fc71368e12d06ba 5e40919a40cb3e590ed45c2a54a4a2518aa88a99 git Not specified
CNA Linux Linux affected 89b768ec2dfefaeba5212de14fc71368e12d06ba e0c3dd7b30cc5ee42ab502da140cda93d794a20b git Not specified
CNA Linux Linux affected 89b768ec2dfefaeba5212de14fc71368e12d06ba acab6314bb75be994f720ed13e9d9139cbf828a8 git Not specified
CNA Linux Linux affected 89b768ec2dfefaeba5212de14fc71368e12d06ba 979c017803c40829b03acd9e5236e354b7622360 git Not specified
CNA Linux Linux affected b3dd82a879f25db9d096ae3053f657aa4260ecc6 git Not specified
CNA Linux Linux affected 6.11.3 6.12 semver Not specified
CNA Linux Linux affected 6.12 Not specified
CNA Linux Linux unaffected 6.12 semver Not specified
CNA Linux Linux unaffected 6.12.92 6.12.* semver Not specified
CNA Linux Linux unaffected 6.18.34 6.18.* semver Not specified
CNA Linux Linux unaffected 7.0.11 7.0.* semver Not specified
CNA Linux Linux unaffected 7.1 * original_commit_for_fix Not specified

References

ReferenceSourceLinkTags
git.kernel.org/stable/c/979c017803c40829b03acd9e5236e354b7622360 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/5e40919a40cb3e590ed45c2a54a4a2518aa88a99 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/e0c3dd7b30cc5ee42ab502da140cda93d794a20b 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/acab6314bb75be994f720ed13e9d9139cbf828a8 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
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