linux-kernel - [BUG] bfq-iosched: possible null-pointer dereference in __bfq_insert

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Date:   Sat, 31 Jul 2021 11:43:20 +0800
From:   Li Tuo <islituo@...il.com>
To:     paolo.valente@...aro.org, axboe@...nel.dk
Cc:     linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        baijiaju1990@...il.com
Subject: [BUG] bfq-iosched: possible null-pointer dereference in
 __bfq_insert_request()

Hello,

Our static analysis tool finds a possible null-pointer dereference in 
bfq-iosched.c in Linux 5.14.0-rc3:

The variable bfqq is checked in:
5920:    waiting = bfqq && bfq_bfqq_wait_request(bfqq);

This indicates that bfqq can be NULL.
But the address of its field fifo, which is an illegal pointer, is 
dereferenced in the function list_add_tail():
5925:    list_add_tail(&rq->queuelist, &bfqq->fifo);

The pointer bfqq is also dereferenced in the function bfq_rq_enqueued() 
which is called at line 5927.
Some dereference operations are:
5826:    bfqq->meta_pending++;
5828:    bfqq->last_request_pos = blk_rq_pos(rq) + blk_rq_sectors(rq);

I am not quite sure whether this possible null-pointer dereference is 
real and how to fix it if it is real.
Any feedback would be appreciated, thanks!

Reported-by: TOTE Robot <oslab@...nghua.edu.cn>

Best wishes,
Tuo Li