In the Linux kernel, the following vulnerability has been resolved:<\/p>\n
net: thunderbolt: Tear down DMA paths before stopping the rings<\/p>\n
tbnet_tear_down() stops both rings and frees their frame buffers before
\ncalling tb_xdomain_disable_paths(). tb_ring_stop() zeroes the ring’s
\ndescriptor base and tbnet_free_buffers() unmaps and frees the pages the
\nframes sit in, so by the time __tb_path_deactivate_hop() polls the hop’s
\n‘pending’ bit, anything still in flight has nowhere to drain to.<\/p>\n
The teardown sequence has been in this order since the driver was added.
\nThe setup path has not: commit ff7cd07f3064 (“net: thunderbolt: Enable
\nDMA paths only after rings are enabled”) moved the path enable to the end
\nof tbnet_connected_work() and documented why:<\/p>\n
\t\/* Both logins successful so enable the rings, high-speed DMA
\n\t * paths and start the network device queue.
\n\t *
\n\t * Note we enable the DMA paths last to make sure we have primed
\n\t * the Rx ring before any incoming packets are allowed to
\n\t * arrive.
\n\t *\/<\/p>\n
Teardown was never updated to match, so the rings and the paths now come
\ndown in the same order they go up instead of in reverse.<\/p>\n
On an ASMedia ASM4242 host router the ‘pending’ bit then never clears:
\nevery teardown burns the full 500 ms timeout and
\n__tb_path_deactivate_hop() returns -ETIMEDOUT. Raising the timeout to
\n5 s does not help, so the hop is not slow to drain, it never drains
\nat all.<\/p>\n
The failure is invisible above the thunderbolt core.
\n__tb_path_deactivate_hops() is void and only calls tb_port_warn();
\ntb_path_deactivate(), tb_tunnel_deactivate() and
\n__tb_disconnect_xdomain_paths() are void as well, and
\ntb_disconnect_xdomain_paths() ends in an unconditional “return 0”. So
\ntb_xdomain_disable_paths() reports success and the netdev_warn() below
\nit never fires. Repeated teardowns eventually take the XDomain control
\nchannel down, after which the peer node is gone and only a power cycle
\nbrings the controller back.<\/p>\n
Deactivating the paths first fixes it. Measured with kretprobes on a
\nstock v6.17 tree with no other patches applied, on a link that was up
\nand had just carried traffic:<\/p>\n
before: __tb_path_deactivate_hop() returns 0 for the first hop, then
\n -ETIMEDOUT for the second 500335 us later
\n after: 0 for both, 525 us apart<\/p>\n
Alternating the two orderings ABBA over three load levels, four
\nteardowns per arm: every teardown failed before the change (21 of 21
\nthat ran), none failed after (0 of 24). The before arms ran short
\nbecause the link died partway through. The same split shows up when
\nthe interface is enslaved to a bond instead of just brought down, which
\nis how I ran into this in the first place. Throughput and latency after
\nthe change are unchanged.<\/p>\n
Hosts whose routers drain the hop despite the stale descriptor base see
\nno functional difference, since the paths end up deactivated either way.<\/p>\n","protected":false},"excerpt":{"rendered":"
In the Linux kernel, the following vulnerability has been resolved:<\/p>\n
net: thunderbolt: Tear down DMA paths before stopping the rings<\/p>\n
tbnet_tear_down() stops both rings and frees their frame buffers b<\/p>\n","protected":false},"template":"","meta":[],"categories":[],"tags":[],"class_list":["post-11265","vuln","type-vuln","status-publish","hentry"],"_links":{"self":[{"href":"https:\/\/www.54iter.cn\/index.php?rest_route=\/wp\/v2\/vuln\/11265","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=11265"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.54iter.cn\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=11265"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.54iter.cn\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=11265"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}