linux-kernel - [PATCH 5.6 018/254] blk-mq: Fix a recently introduced regression in blk_mq_realloc_hw

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Message-Id: <20200416131328.079987030@linuxfoundation.org>
Date:   Thu, 16 Apr 2020 15:21:47 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Bart Van Assche <bvanassche@....org>,
        Ming Lei <ming.lei@...hat.com>,
        Keith Busch <kbusch@...nel.org>,
        Johannes Thumshirn <jth@...nel.org>,
        Hannes Reinecke <hare@...e.com>,
        Christoph Hellwig <hch@...radead.org>,
        Jens Axboe <axboe@...nel.dk>, Sasha Levin <sashal@...nel.org>
Subject: [PATCH 5.6 018/254] blk-mq: Fix a recently introduced regression in blk_mq_realloc_hw_ctxs()

From: Bart Van Assche <bvanassche@....org>

[ Upstream commit d0930bb8f46b8fb4a7d429c0bf1c91b3ed00a7cf ]

q->nr_hw_queues must only be updated once it is known that
blk_mq_realloc_hw_ctxs() has succeeded. Otherwise it can happen that
reallocation fails and that q->nr_hw_queues is larger than the number of
allocated hardware queues. This patch fixes the following crash if
increasing the number of hardware queues fails:

BUG: KASAN: null-ptr-deref in blk_mq_map_swqueue+0x775/0x810
Write of size 8 at addr 0000000000000118 by task check/977

CPU: 3 PID: 977 Comm: check Not tainted 5.6.0-rc1-dbg+ #8
Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
Call Trace:
 dump_stack+0xa5/0xe6
 __kasan_report.cold+0x65/0x99
 kasan_report+0x16/0x20
 check_memory_region+0x140/0x1b0
 memset+0x28/0x40
 blk_mq_map_swqueue+0x775/0x810
 blk_mq_update_nr_hw_queues+0x468/0x710
 nullb_device_submit_queues_store+0xf7/0x1a0 [null_blk]
 configfs_write_file+0x1c4/0x250 [configfs]
 __vfs_write+0x4c/0x90
 vfs_write+0x145/0x2c0
 ksys_write+0xd7/0x180
 __x64_sys_write+0x47/0x50
 do_syscall_64+0x6f/0x2f0
 entry_SYSCALL_64_after_hwframe+0x49/0xbe

Fixes: ac0d6b926e74 ("block: Reduce the amount of memory required per request queue")
Signed-off-by: Bart Van Assche <bvanassche@....org>
Reviewed-by: Ming Lei <ming.lei@...hat.com>
Cc: Keith Busch <kbusch@...nel.org>
Cc: Johannes Thumshirn <jth@...nel.org>
Cc: Hannes Reinecke <hare@...e.com>
Cc: Christoph Hellwig <hch@...radead.org>
Signed-off-by: Jens Axboe <axboe@...nel.dk>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 block/blk-mq.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index d4bd9b961726a..37ff8dfb8ab9f 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -2824,7 +2824,6 @@ static void blk_mq_realloc_hw_ctxs(struct blk_mq_tag_set *set,
 			memcpy(new_hctxs, hctxs, q->nr_hw_queues *
 			       sizeof(*hctxs));
 		q->queue_hw_ctx = new_hctxs;
-		q->nr_hw_queues = set->nr_hw_queues;
 		kfree(hctxs);
 		hctxs = new_hctxs;
 	}
-- 
2.20.1