In the Linux kernel, the following vulnerability has been resolved:<\/p>\n
net\/rds: acquire the fastpath locks in rds_conn_shutdown()<\/p>\n
rds_conn_shutdown() quiesces the transmit and receive-refill paths by
\nwaiting for RDS_IN_XMIT and RDS_RECV_REFILL to be sampled clear, and
\nthen runs the transport shutdown and rds_conn_path_reset(). Sampling
\nthe bits clear is not the same as owning them: the moment after the
\nwait_event() returns, rds_send_xmit() can re-acquire RDS_IN_XMIT (or
\nrds_ib_recv_refill() can re-acquire RDS_RECV_REFILL) and run
\nconcurrently with the teardown.<\/p>\n
The sender does recheck the connection state after taking the lock,
\nbut that recheck is a classic store-buffering pattern: teardown writes
\nthe state and reads the bit while the sender writes the bit and reads
\nthe state. acquire_in_xmit() is only an acquire operation, so on
\nweakly ordered architectures both sides can miss each other’s write,
\nand the transmit path then runs while the transport zeroes its rings
\n(e.g. rds_ib_ring_init()) and rds_send_path_reset() rewrites the
\ntransmit state under it.<\/p>\n
Oracle UEK fixed the same class of crashes – a 14-year tail of
\nBUG_ON()s in rds_ib_sub_signaled(), unexpected op-codes and NULL
\ndereferences in rds_ib_send_cqe_handler() during failover testing –
\nby making the teardown path *acquire* the fastpath bit locks instead
\nof testing them (“rds: Make sure transmit path and connection
\ntear-down does not run concurrently”). Ownership of a single word is
\ndecided by RMW atomicity, so no cross-variable ordering is needed.<\/p>\n
Do the same here: take both locks before calling the transport
\nshutdown, hold them across rds_conn_path_reset(), and release them
\nexplicitly with a wake-up afterwards. Both are released with
\nclear_bit_unlock(), so that the ring re-initialization done by the
\ntransport shutdown and the transmit state rewritten by
\nrds_send_path_reset() are ordered before either bit is seen clear by
\nthe next acquire_in_xmit() or acquire_refill().<\/p>\n
The fastpath users of these bits – rds_send_xmit() and
\nrds_ib_recv_refill() – are trylock style and back off while teardown
\nowns the locks, so no new lock dependency is introduced for them.
\nrds_tcp_reset_callbacks() is different: since the previous patch it
\nacquires RDS_IN_XMIT as well, and it blocks doing so, so its wait now
\nspans the teardown instead of at most one send batch. That waiter
\nruns from rds_tcp_accept_one() on the single-threaded krdsd workqueue
\nand holds rds_tcp_accept_lock and t_conn_path_lock while it waits, so
\na duelling SYN accepted while its path is being torn down parks
\naccept processing for the duration of the teardown – for TCP bounded
\nby the (up to 5 s) drain loop in rds_tcp_conn_path_shutdown(). An IB
\npath’s drain in rds_ib_conn_path_shutdown() has no round cap, but no
\nblocking waiter either: rds_tcp_reset_callbacks() is the only blocking
\nacquirer of these bits and waits only on its own TCP path, and the
\nfastpaths are trylock-and-back-off on both transports, so a long IB
\ndrain lengthens only that path’s own quiesce. The
\nwindow is narrow: the accept-side state check has to pass before the
\nteardown moves the path to RDS_CONN_DISCONNECTING.<\/p>\n
Because krdsd is a single global workqueue, everything else queued
\nthere – accept processing for other connections and network
\nnamespaces, and the flush_workqueue(rds_wq) in rds_tcp_listen_stop()
\nduring namespace teardown – waits behind the parked accept worker for
\nthat time. It cannot deadlock, although the waits do point at each
\nother: the teardown blocks until the bit’s holder releases it, and
\nthe holder may be that krdsd accept worker. The holder finishes
\nwithout needing anything the teardown owns: the sync cancels
\nrds_tcp_reset_callbacks() issues target cp_send_w and cp_recv_w on
\nthe path’s ordered cp_wq, whose only execution slot is occupied by
\nthe blocked cp_down_w itself, so they are pending at most and cancel
\nwithout flushing – a reliance on cp_wq being ordered that is now
\nnoted next to those cancels (on
\n—truncated—<\/p>\n","protected":false},"excerpt":{"rendered":"
In the Linux kernel, the following vulnerability has been resolved:<\/p>\n
net\/rds: acquire the fastpath locks in rds_conn_shutdown()<\/p>\n
rds_conn_shutdown() quiesces the transmit and receive-refill paths by
\nw<\/p>\n","protected":false},"template":"","meta":[],"categories":[],"tags":[],"class_list":["post-29224","vuln","type-vuln","status-publish","hentry"],"_links":{"self":[{"href":"https:\/\/www.54iter.cn\/index.php?rest_route=\/wp\/v2\/vuln\/29224","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=29224"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.54iter.cn\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=29224"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.54iter.cn\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=29224"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}