In the Linux kernel, the following vulnerability has been resolved:<\/p>\n
ppp: defer channel free to an RCU grace period to fix pppol2tp RX UAF<\/p>\n
pppol2tp_recv() runs in the L2TP UDP-encap softirq RX path:<\/p>\n
l2tp_udp_encap_recv() -> l2tp_recv_common() -> pppol2tp_recv()
\n -> ppp_input(&po->chan)<\/p>\n
It runs under rcu_read_lock() holding only an l2tp_session reference and
\ntakes NO reference on the internal PPP channel (struct channel,
\nchan->ppp) that ppp_input() dereferences.<\/p>\n
The pppox socket is SOCK_RCU_FREE, so ‘po’ and the embedded ppp_channel
\nare RCU-safe. But the internal struct channel is a separate allocation
\nthat ppp_release_channel() frees with a plain kfree():<\/p>\n
close(data socket) -> pppol2tp_release() -> pppox_unbind_sock()
\n -> ppp_unregister_channel() -> ppp_release_channel() -> kfree(pch)<\/p>\n
For a channel that is bound (PPPIOCGCHAN) but not attached to a ppp unit
\n(no PPPIOCCONNECT, pch->ppp == NULL) and not bridged, teardown skips
\nboth ppp_disconnect_channel()’s synchronize_net() and
\nppp_unbridge_channels()’s synchronize_rcu(), so the kfree() has no grace
\nperiod. rcu_read_lock() in pppol2tp_recv() does not protect against a
\nplain kfree(), so an in-flight ppp_input() on one CPU can dereference
\nthe channel just freed by close() on another CPU.<\/p>\n
The bug is reachable by an unprivileged user.<\/p>\n
Defer the channel free to an RCU callback via call_rcu() so the grace
\nperiod fences any in-flight ppp_input(). The disconnect and unbridge
\nteardown paths already fence with synchronize_net()\/synchronize_rcu();
\ncall_rcu() does the same here without stalling the close() path.<\/p>\n","protected":false},"excerpt":{"rendered":"
In the Linux kernel, the following vulnerability has been resolved:<\/p>\n
ppp: defer channel free to an RCU grace period to fix pppol2tp RX UAF<\/p>\n
pppol2tp_recv() runs in the L2TP UDP-encap softirq RX path:<\/p>\n","protected":false},"template":"","meta":[],"categories":[],"tags":[],"class_list":["post-5460","vuln","type-vuln","status-publish","hentry"],"_links":{"self":[{"href":"https:\/\/www.54iter.cn\/index.php?rest_route=\/wp\/v2\/vuln\/5460","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=5460"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.54iter.cn\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=5460"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.54iter.cn\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=5460"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}