In the Linux kernel, the following vulnerability has been resolved:<\/p>\n
l2tp: use refcount_inc_not_zero in l2tp_session_get_by_ifname<\/p>\n
A reader in l2tp_session_get_by_ifname() can return a pointer to a
\nsession whose refcount has reached zero. The getter takes its
\nreference with plain refcount_inc(), but every other session getter
\nin the same file (l2tp_v2_session_get, l2tp_v3_session_get, and the
\ncorresponding _get_next variants) uses refcount_inc_not_zero()
\nbecause the IDR\/RCU lookup can race with refcount_dec_and_test() ->
\nl2tp_session_free() -> kfree_rcu(). The ifname getter is the only
\noutlier; the inconsistency was raised on-list after 979c017803c4
\n(“l2tp: use list_del_rcu in l2tp_session_unhash”).<\/p>\n
A reader inside rcu_read_lock_bh() that matches session->ifname can
\nbe preempted between the strcmp() and the refcount_inc(). If the
\nlast reference drops on another CPU in that window, the reader’s
\nrefcount_inc() runs on a counter that has reached zero. refcount_t
\ncatches the addition-on-zero, prints “refcount_t: addition on 0;
\nuse-after-free”, saturates the counter, and returns the saturated
\npointer to the caller. Session memory is held live by the in-flight
\nRCU read section, but the kfree_rcu() callback queued from
\nl2tp_session_free() will free it once the grace period closes; a
\ncaller that dereferences the returned session past that point hits
\na slab-use-after-free. On PREEMPT_RT local_bh_disable() is a per-CPU
\nsleeping lock and the preemption window is real; on stock PREEMPT
\nkernels local_bh_disable() is a preempt_count increment that closes
\nthe cross-CPU race in practice (see below).<\/p>\n
Use refcount_inc_not_zero() and continue the list walk on failure,
\nmatching the other session getters in the file. The ifname getter
\nis the only session getter in net\/l2tp\/ that still uses the bare
\nrefcount_inc() pattern; this change restores file-internal
\nconsistency. The success path is unchanged.<\/p>\n","protected":false},"excerpt":{"rendered":"
In the Linux kernel, the following vulnerability has been resolved:<\/p>\n
l2tp: use refcount_inc_not_zero in l2tp_session_get_by_ifname<\/p>\n
A reader in l2tp_session_get_by_ifname() can return a pointer to a
\ns<\/p>\n","protected":false},"template":"","meta":[],"categories":[],"tags":[],"class_list":["post-14956","vuln","type-vuln","status-publish","hentry"],"_links":{"self":[{"href":"https:\/\/www.54iter.cn\/index.php?rest_route=\/wp\/v2\/vuln\/14956","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.54iter.cn\/index.php?rest_route=\/wp\/v2\/vuln"}],"about":[{"href":"https:\/\/www.54iter.cn\/index.php?rest_route=\/wp\/v2\/types\/vuln"}],"wp:attachment":[{"href":"https:\/\/www.54iter.cn\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=14956"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.54iter.cn\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=14956"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.54iter.cn\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=14956"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}