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Date: Thu, 26 Nov 2020 20:32:05 +0530 From: Pradeep P V K <ppvk@...eaurora.org> To: axboe@...nel.dk, linux-block@...r.kernel.org Cc: stummala@...eaurora.org, linux-kernel@...r.kernel.org, Pradeep P V K <ppvk@...eaurora.org> Subject: [PATCH V1] block: Fix use-after-free while iterating over requests Observes below crash while accessing (use-after-free) request queue member of struct request. 191.784789: <2> Unable to handle kernel paging request at virtual address ffffff81429a4440 ... 191.786174: <2> CPU: 3 PID: 213 Comm: kworker/3:1H Tainted: G S O 5.4.61-qgki-debug-ge45de39 #1 ... 191.786226: <2> Workqueue: kblockd blk_mq_timeout_work 191.786242: <2> pstate: 20c00005 (nzCv daif +PAN +UAO) 191.786261: <2> pc : bt_for_each+0x114/0x1a4 191.786274: <2> lr : bt_for_each+0xe0/0x1a4 ... 191.786494: <2> Call trace: 191.786507: <2> bt_for_each+0x114/0x1a4 191.786519: <2> blk_mq_queue_tag_busy_iter+0x60/0xd4 191.786532: <2> blk_mq_timeout_work+0x54/0xe8 191.786549: <2> process_one_work+0x2cc/0x568 191.786562: <2> worker_thread+0x28c/0x518 191.786577: <2> kthread+0x160/0x170 191.786594: <2> ret_from_fork+0x10/0x18 191.786615: <2> Code: 0b080148 f9404929 f8685921 b4fffe01 (f9400028) 191.786630: <2> ---[ end trace 0f1f51d79ab3f955 ]--- 191.786643: <2> Kernel panic - not syncing: Fatal exception Fix this by updating the freed request with NULL. This could avoid accessing the already free request from other contexts while iterating over the requests. Signed-off-by: Pradeep P V K <ppvk@...eaurora.org> --- block/blk-mq.c | 1 + block/blk-mq.h | 1 + 2 files changed, 2 insertions(+) diff --git a/block/blk-mq.c b/block/blk-mq.c index 55bcee5..9996cb1 100644 --- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -492,6 +492,7 @@ static void __blk_mq_free_request(struct request *rq) blk_crypto_free_request(rq); blk_pm_mark_last_busy(rq); + hctx->tags->rqs[rq->tag] = NULL; rq->mq_hctx = NULL; if (rq->tag != BLK_MQ_NO_TAG) blk_mq_put_tag(hctx->tags, ctx, rq->tag); diff --git a/block/blk-mq.h b/block/blk-mq.h index a52703c..8747bf1 100644 --- a/block/blk-mq.h +++ b/block/blk-mq.h @@ -224,6 +224,7 @@ static inline int __blk_mq_active_requests(struct blk_mq_hw_ctx *hctx) static inline void __blk_mq_put_driver_tag(struct blk_mq_hw_ctx *hctx, struct request *rq) { + hctx->tags->rqs[rq->tag] = NULL; blk_mq_put_tag(hctx->tags, rq->mq_ctx, rq->tag); rq->tag = BLK_MQ_NO_TAG; -- 2.7.4
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