In the Linux kernel, the following vulnerability has been resolved:<\/p>\n
net: openvswitch: fix flow mask use-after-free on flow deletion<\/p>\n
The commit in the Fixes tag below made so flow->mask free is scheduled
\nvia RCU right after it is removed from the flow table. The pointer
\nstays in the flow structure and it can be accessible while in the same
\nRCU critical section. This is done to avoid requiring ovs_mutex for
\nthe ovs_flow_free().<\/p>\n
However, while removing the flow during processing of CMD_DEL, we do
\nnot take RCU read lock before the removal, and ovs_flow_cmd_fill_info()
\nuses the flow->mask pointer afterwards. The RCU read lock is taken,
\nbut it’s already late at that point. The comment on that line
\nacknowledges that the lock is cosmetic and doesn’t serve a real purpose.<\/p>\n
This leads to use-after-free if the RCU grace period passes between
\nremoval and the filling. It is a short race window, but it is there
\nand can lead to a real crash in case memory allocation for the info
\ntakes a bit longer:<\/p>\n
BUG: KASAN: slab-use-after-free in __ovs_nla_put_key
\n net\/openvswitch\/flow_netlink.c:1996
\n BUG: KASAN: slab-use-after-free in ovs_nla_put_key+0x2463\/0x2e30
\n net\/openvswitch\/flow_netlink.c:2250
\n Read of size 4 at addr ffff88801ee89970 by task ovs_flow_del_ec\/9487<\/p>\n
Call Trace:<\/p>\n
__ovs_nla_put_key net\/openvswitch\/flow_netlink.c:1996
\n ovs_nla_put_key+0x2463\/0x2e30 net\/openvswitch\/flow_netlink.c:2250
\n ovs_flow_cmd_fill_info+0x420\/0x9c0 net\/openvswitch\/datapath.c:930
\n ovs_flow_cmd_del+0x53a\/0x970 net\/openvswitch\/datapath.c:1467
\n …
\n netlink_rcv_skb+0x156\/0x420 net\/netlink\/af_netlink.c:2556<\/p>\n
Allocated by task 9487:
\n mask_alloc net\/openvswitch\/flow_table.c:967
\n flow_mask_insert net\/openvswitch\/flow_table.c:1012
\n ovs_flow_tbl_insert+0xea2\/0x1a90 net\/openvswitch\/flow_table.c:1084
\n ovs_flow_cmd_new+0x7e3\/0xd90 net\/openvswitch\/datapath.c:1086
\n …
\n netlink_rcv_skb+0x156\/0x420 net\/netlink\/af_netlink.c:2556<\/p>\n
Freed by task 9485:
\n rcu_free_sheaf+0x1e\/0x100 mm\/slub.c:5978
\n rcu_do_batch kernel\/rcu\/tree.c:2645
\n rcu_core+0x59c\/0x10c0 kernel\/rcu\/tree.c:2897
\n handle_softirqs+0x1e4\/0x9a0 kernel\/softirq.c:622
\n …
\n instr_sysvec_apic_timer_interrupt arch\/x86\/kernel\/apic\/apic.c:1062<\/p>\n
ovs_flow_tbl_remove() must be called after the ovs_flow_cmd_fill_info()
\nto avoid this race. This also helps with cleaning up the forced cast
\nand the cosmetic RCU read lock. Before the commit in the Fixes tag the
\norder did not matter as long as the flow object itself was not freed.<\/p>\n
A wider RCU critical section could be another option, but we have a
\nGFP_KERNEL allocation in the way.<\/p>\n
Reported by Trend Micro’s Zero Day Initiative as ZDI-CAN-32042.<\/p>\n","protected":false},"excerpt":{"rendered":"
In the Linux kernel, the following vulnerability has been resolved:<\/p>\n
net: openvswitch: fix flow mask use-after-free on flow deletion<\/p>\n
The commit in the Fixes tag below made so flow->mask free is sched<\/p>\n","protected":false},"template":"","meta":[],"categories":[],"tags":[],"class_list":["post-21327","vuln","type-vuln","status-publish","hentry"],"_links":{"self":[{"href":"https:\/\/www.54iter.cn\/index.php?rest_route=\/wp\/v2\/vuln\/21327","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=21327"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.54iter.cn\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=21327"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.54iter.cn\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=21327"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}