From d29bd41428cfff9b582c248db14a47e2be8457a8 Mon Sep 17 00:00:00 2001 From: Paolo Valente Date: Fri, 15 Oct 2021 16:43:36 +0200 Subject: [PATCH] block, bfq: reset last_bfqq_created on group change Since commit 430a67f9d616 ("block, bfq: merge bursts of newly-created queues"), BFQ maintains a per-group pointer to the last bfq_queue created. If such a queue, say bfqq, happens to move to a different group, then bfqq is no more a valid last bfq_queue created for its previous group. That pointer must then be cleared. Not resetting such a pointer may also cause UAF, if bfqq happens to also be freed after being moved to a different group. This commit performs this missing reset. As such it fixes commit 430a67f9d616 ("block, bfq: merge bursts of newly-created queues"). Such a missing reset is most likely the cause of the crash reported in [1]. With some analysis, we found that this crash was due to the above UAF. And such UAF did go away with this commit applied [1]. Anyway, before this commit, that crash happened to be triggered in conjunction with commit 2d52c58b9c9b ("block, bfq: honor already-setup queue merges"). The latter was then reverted by commit ebc69e897e17 ("Revert "block, bfq: honor already-setup queue merges""). Yet commit 2d52c58b9c9b ("block, bfq: honor already-setup queue merges") contains no error related with the above UAF, and can then be restored. [1] https://bugzilla.kernel.org/show_bug.cgi?id=214503 Fixes: 430a67f9d616 ("block, bfq: merge bursts of newly-created queues") Tested-by: Grzegorz Kowal Signed-off-by: Paolo Valente Link: https://lore.kernel.org/r/20211015144336.45894-2-paolo.valente@linaro.org Signed-off-by: Jens Axboe --- block/bfq-cgroup.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/block/bfq-cgroup.c b/block/bfq-cgroup.c index e2f14508f2d6..85b8e1c3a762 100644 --- a/block/bfq-cgroup.c +++ b/block/bfq-cgroup.c @@ -666,6 +666,12 @@ void bfq_bfqq_move(struct bfq_data *bfqd, struct bfq_queue *bfqq, bfq_put_idle_entity(bfq_entity_service_tree(entity), entity); bfqg_and_blkg_put(bfqq_group(bfqq)); + if (entity->parent && + entity->parent->last_bfqq_created == bfqq) + entity->parent->last_bfqq_created = NULL; + else if (bfqd->last_bfqq_created == bfqq) + bfqd->last_bfqq_created = NULL; + entity->parent = bfqg->my_entity; entity->sched_data = &bfqg->sched_data; /* pin down bfqg and its associated blkg */