In the Linux kernel, the following vulnerability has been resolved:<\/p>\n
flow_dissector: check device type before reading ETH_ADDRS<\/p>\n
__skb_flow_dissect() unconditionally reads 12 bytes from eth_hdr(skb)
\nwhen FLOW_DISSECTOR_KEY_ETH_ADDRS is requested. This assumes the skb
\nhas a valid Ethernet header at mac_header, which is not always the case.<\/p>\n
The problem can be triggered by:
\n 1. Creating a TUN device in L3 mode (IFF_TUN, hard_header_len=0)
\n 2. Attaching a multiq qdisc with a flower filter matching on eth_src
\n 3. Sending a packet through AF_PACKET<\/p>\n
Since TUN in L3 mode has no link-layer header, mac_header points to
\nthe L3 data area. The flow dissector reads 12 bytes of uninitialized
\nskb memory, which then propagates through fl_set_masked_key() and is
\nused as a rhashtable lookup key in __fl_lookup(), as reported by KMSAN.<\/p>\n
Rejecting the filter in the control path (at tc filter add time) is
\nnot feasible because TC filter blocks can be shared between arbitrary
\ndevices — a filter installed on an Ethernet device may later classify
\npackets on a headerless device through a shared block. The device
\nassociation is not fixed at filter creation time.<\/p>\n
Fix this by gating the memcpy on dev->type == ARPHRD_ETHER, which
\nensures only true Ethernet-framed packets have their addresses read.
\nThis is more precise than the previous hard_header_len >= 12 check,
\nwhich would incorrectly pass for non-Ethernet link types like IPoIB
\n(ARPHRD_INFINIBAND, hard_header_len=24) and FDDI (hard_header_len=21)
\nwhose L2 headers are not in Ethernet format. Additionally check
\nskb_mac_header_was_set() to guard against the pathological case where
\nmac_header is the unset sentinel (~0U), which would cause eth_hdr() to
\nreturn a wild pointer.<\/p>\n
For the act_mirred redirect case (Ethernet packet redirected to a
\nnon-Ethernet device sharing a TC block), zeroing the key is the correct
\nbehavior: the packet is now being classified on the target device, where
\nEthernet address matching is not semantically meaningful.<\/p>\n
Note: on non-Ethernet devices, the zeroed key will match a filter
\nconfigured with all-zero MAC addresses. This is an improvement over the
\nprevious behavior where uninitialized memory could randomly match any
\nfilter.<\/p>\n","protected":false},"excerpt":{"rendered":"
In the Linux kernel, the following vulnerability has been resolved:<\/p>\n
flow_dissector: check device type before reading ETH_ADDRS<\/p>\n
__skb_flow_dissect() unconditionally reads 12 bytes from eth_hdr(skb)
\nw<\/p>\n","protected":false},"template":"","meta":[],"categories":[],"tags":[],"class_list":["post-7103","vuln","type-vuln","status-publish","hentry"],"_links":{"self":[{"href":"https:\/\/www.54iter.cn\/index.php?rest_route=\/wp\/v2\/vuln\/7103","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=7103"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.54iter.cn\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=7103"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.54iter.cn\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=7103"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}