76 lines
3.0 KiB
Diff
76 lines
3.0 KiB
Diff
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From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
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From: Ming Lei <ming.lei@redhat.com>
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Date: Fri, 10 Sep 2021 14:30:15 +0200
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Subject: [PATCH] blk-mq: fix kernel panic during iterating over flush request
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commit c2da19ed50554ce52ecbad3655c98371fe58599f upstream.
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For fixing use-after-free during iterating over requests, we grabbed
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request's refcount before calling ->fn in commit 2e315dc07df0 ("blk-mq:
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grab rq->refcount before calling ->fn in blk_mq_tagset_busy_iter").
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Turns out this way may cause kernel panic when iterating over one flush
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request:
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1) old flush request's tag is just released, and this tag is reused by
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one new request, but ->rqs[] isn't updated yet
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2) the flush request can be re-used for submitting one new flush command,
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so blk_rq_init() is called at the same time
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3) meantime blk_mq_queue_tag_busy_iter() is called, and old flush request
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is retrieved from ->rqs[tag]; when blk_mq_put_rq_ref() is called,
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flush_rq->end_io may not be updated yet, so NULL pointer dereference
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is triggered in blk_mq_put_rq_ref().
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Fix the issue by calling refcount_set(&flush_rq->ref, 1) after
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flush_rq->end_io is set. So far the only other caller of blk_rq_init() is
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scsi_ioctl_reset() in which the request doesn't enter block IO stack and
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the request reference count isn't used, so the change is safe.
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Fixes: 2e315dc07df0 ("blk-mq: grab rq->refcount before calling ->fn in blk_mq_tagset_busy_iter")
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Reported-by: "Blank-Burian, Markus, Dr." <blankburian@uni-muenster.de>
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Tested-by: "Blank-Burian, Markus, Dr." <blankburian@uni-muenster.de>
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Signed-off-by: Ming Lei <ming.lei@redhat.com>
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Reviewed-by: Christoph Hellwig <hch@lst.de>
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Reviewed-by: John Garry <john.garry@huawei.com>
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Link: https://lore.kernel.org/r/20210811142624.618598-1-ming.lei@redhat.com
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Signed-off-by: Jens Axboe <axboe@kernel.dk>
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Cc: Yi Zhang <yi.zhang@redhat.com>
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Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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---
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block/blk-core.c | 1 -
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block/blk-flush.c | 8 ++++++++
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2 files changed, 8 insertions(+), 1 deletion(-)
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diff --git a/block/blk-core.c b/block/blk-core.c
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index 7663a9b94b80..debdf9b0bf30 100644
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--- a/block/blk-core.c
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+++ b/block/blk-core.c
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@@ -121,7 +121,6 @@ void blk_rq_init(struct request_queue *q, struct request *rq)
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rq->internal_tag = BLK_MQ_NO_TAG;
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rq->start_time_ns = ktime_get_ns();
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rq->part = NULL;
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- refcount_set(&rq->ref, 1);
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blk_crypto_rq_set_defaults(rq);
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}
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EXPORT_SYMBOL(blk_rq_init);
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diff --git a/block/blk-flush.c b/block/blk-flush.c
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index e89d007dbf6a..8b11ab3b3762 100644
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--- a/block/blk-flush.c
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+++ b/block/blk-flush.c
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@@ -329,6 +329,14 @@ static void blk_kick_flush(struct request_queue *q, struct blk_flush_queue *fq,
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flush_rq->rq_flags |= RQF_FLUSH_SEQ;
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flush_rq->rq_disk = first_rq->rq_disk;
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flush_rq->end_io = flush_end_io;
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+ /*
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+ * Order WRITE ->end_io and WRITE rq->ref, and its pair is the one
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+ * implied in refcount_inc_not_zero() called from
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+ * blk_mq_find_and_get_req(), which orders WRITE/READ flush_rq->ref
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+ * and READ flush_rq->end_io
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+ */
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+ smp_wmb();
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+ refcount_set(&flush_rq->ref, 1);
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blk_flush_queue_rq(flush_rq, false);
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}
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