This is a note to let you know that I've just added the patch titled [PATCH stable 5.9 15/24] net/smc: fix use-after-free of delayed events to the 5.9-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: net-smc-fix-use-after-free-of-delayed-events.patch and it can be found in the queue-5.9 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From foo@baz Sat Oct 17 08:52:03 AM CEST 2020 From: Karsten Graul <kgraul@xxxxxxxxxxxxx> Date: Wed, 14 Oct 2020 19:43:27 +0200 Subject: [PATCH stable 5.9 15/24] net/smc: fix use-after-free of delayed events From: Karsten Graul <kgraul@xxxxxxxxxxxxx> [ Upstream commit d535ca1367787ddc8bff22d679a11f864c8228bc ] When a delayed event is enqueued then the event worker will send this event the next time it is running and no other flow is currently active. The event handler is called for the delayed event, and the pointer to the event keeps set in lgr->delayed_event. This pointer is cleared later in the processing by smc_llc_flow_start(). This can lead to a use-after-free condition when the processing does not reach smc_llc_flow_start(), but frees the event because of an error situation. Then the delayed_event pointer is still set but the event is freed. Fix this by always clearing the delayed event pointer when the event is provided to the event handler for processing, and remove the code to clear it in smc_llc_flow_start(). Fixes: 555da9af827d ("net/smc: add event-based llc_flow framework") Signed-off-by: Karsten Graul <kgraul@xxxxxxxxxxxxx> Signed-off-by: Jakub Kicinski <kuba@xxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- net/smc/smc_llc.c | 13 +++++-------- 1 file changed, 5 insertions(+), 8 deletions(-) --- a/net/smc/smc_llc.c +++ b/net/smc/smc_llc.c @@ -233,8 +233,6 @@ static bool smc_llc_flow_start(struct sm default: flow->type = SMC_LLC_FLOW_NONE; } - if (qentry == lgr->delayed_event) - lgr->delayed_event = NULL; smc_llc_flow_qentry_set(flow, qentry); spin_unlock_bh(&lgr->llc_flow_lock); return true; @@ -1603,13 +1601,12 @@ static void smc_llc_event_work(struct wo struct smc_llc_qentry *qentry; if (!lgr->llc_flow_lcl.type && lgr->delayed_event) { - if (smc_link_usable(lgr->delayed_event->link)) { - smc_llc_event_handler(lgr->delayed_event); - } else { - qentry = lgr->delayed_event; - lgr->delayed_event = NULL; + qentry = lgr->delayed_event; + lgr->delayed_event = NULL; + if (smc_link_usable(qentry->link)) + smc_llc_event_handler(qentry); + else kfree(qentry); - } } again: Patches currently in stable-queue which might be from kgraul@xxxxxxxxxxxxx are queue-5.9/net-smc-fix-valid-dmbe-buffer-sizes.patch queue-5.9/net-smc-fix-use-after-free-of-delayed-events.patch