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SubjectRe: [RFC PATCH 1/6] bsg: fix kernel panic resulting from missing allocation of a reply-buffer
Hey Christoph,

I looked over the patch in detail, see below.

> From f5b03b82df0569c035022c1c2535696186907f1a Mon Sep 17 00:00:00 2001
> From: Christoph Hellwig <hch@lst.de>
> Date: Fri, 11 Aug 2017 11:03:29 +0200
> Subject: bsg-lib: allocate sense data for each request
>
> Since we split the scsi_request out of the request the driver is supposed
> to provide storage for the sense buffer. The bsg-lib code failed to do so,
> though and will crash anytime it is used.
>
> This patch moves bsg-lib to allocate and setup the bsg_job ahead of time,
> and allocate the sense data, which is used as reply buffer in bsg.
>
> Reported-by: Steffen Maier <maier@linux.vnet.ibm.com>
> Signed-off-by: Benjamin Block <bblock@linux.vnet.ibm.com>
> Fixes: 82ed4db499b8 ("block: split scsi_request out of struct request")
> Cc: <stable@vger.kernel.org> #4.11+
> ---
> block/bsg-lib.c | 51 +++++++++++++++++++++++++++----------------------
> include/linux/blkdev.h | 1 -
> include/linux/bsg-lib.h | 2 ++
> 3 files changed, 30 insertions(+), 24 deletions(-)
>
> diff --git a/block/bsg-lib.c b/block/bsg-lib.c
> index c4513b23f57a..c07333c3b785 100644
> --- a/block/bsg-lib.c
> +++ b/block/bsg-lib.c
> @@ -37,13 +37,11 @@ static void bsg_destroy_job(struct kref *kref)
> struct bsg_job *job = container_of(kref, struct bsg_job, kref);
> struct request *rq = job->req;
>
> - blk_end_request_all(rq, BLK_STS_OK);
> -
> put_device(job->dev); /* release reference for the request */
>
> kfree(job->request_payload.sg_list);
> kfree(job->reply_payload.sg_list);
> - kfree(job);
> + blk_end_request_all(rq, BLK_STS_OK);

What is the reason for moving that last line? Just wondering whether
that might change the behavior somehow, although it doesn't look like it
from the code.

> }
>
> void bsg_job_put(struct bsg_job *job)
> @@ -100,7 +98,7 @@ EXPORT_SYMBOL_GPL(bsg_job_done);
> */
> static void bsg_softirq_done(struct request *rq)
> {
> - struct bsg_job *job = rq->special;
> + struct bsg_job *job = blk_mq_rq_to_pdu(rq);
>
> bsg_job_put(job);
> }
> @@ -129,24 +127,11 @@ static int bsg_map_buffer(struct bsg_buffer *buf, struct request *req)
> static int bsg_create_job(struct device *dev, struct request *req)
> {
> struct request *rsp = req->next_rq;
> - struct request_queue *q = req->q;
> + struct bsg_job *job = blk_mq_rq_to_pdu(req);
> struct scsi_request *rq = scsi_req(req);
> - struct bsg_job *job;
> int ret;
>
> - BUG_ON(req->special);
> -
> - job = kzalloc(sizeof(struct bsg_job) + q->bsg_job_size, GFP_KERNEL);
> - if (!job)
> - return -ENOMEM;
> -
> - req->special = job;
> - job->req = req;
> - if (q->bsg_job_size)
> - job->dd_data = (void *)&job[1];
> - job->request = rq->cmd;
> job->request_len = rq->cmd_len;
> - job->reply = rq->sense;
> job->reply_len = SCSI_SENSE_BUFFERSIZE; /* Size of sense buffer
> * allocated */
> if (req->bio) {
> @@ -187,7 +172,6 @@ static void bsg_request_fn(struct request_queue *q)
> {
> struct device *dev = q->queuedata;
> struct request *req;
> - struct bsg_job *job;
> int ret;
>
> if (!get_device(dev))
> @@ -207,8 +191,7 @@ static void bsg_request_fn(struct request_queue *q)
> continue;
> }
>
> - job = req->special;
> - ret = q->bsg_job_fn(job);
> + ret = q->bsg_job_fn(blk_mq_rq_to_pdu(req));
> spin_lock_irq(q->queue_lock);
> if (ret)
> break;
> @@ -219,6 +202,27 @@ static void bsg_request_fn(struct request_queue *q)
> spin_lock_irq(q->queue_lock);
> }
>
> +static int bsg_init_rq(struct request_queue *q, struct request *req, gfp_t gfp)
> +{
> + struct bsg_job *job = blk_mq_rq_to_pdu(req);
> +
> + memset(job, 0, sizeof(*job));
> + job->req = req;
> + job->request = job->sreq.cmd;

That doesn't work with bsg.c if the request submitted by the user is
bigger than BLK_MAX_CDB. There is code in blk_fill_sgv4_hdr_rq() that
will reassign the req->cmd point in that case to something else.

This is maybe wrong in the same vein as my Patch 1 is. If not for the
legacy code in bsg.c, setting this here, will miss changes to that
pointer between request-allocation and job-submission.

So maybe just move this to bsg_create_job().

> + job->dd_data = job + 1;
> + job->reply = job->sreq.sense = kzalloc(job->reply_len, gfp);

job->reply_len will be 0 here, won't it? You probably have to pull the
"job->reply_len = SCSI_SENSE_BUFFERSIZE" here from bsg_create_job().

> + if (!job->reply)
> + return -ENOMEM;
> + return 0;
> +}
> +
> +static void bsg_exit_rq(struct request_queue *q, struct request *req)
> +{
> + struct bsg_job *job = blk_mq_rq_to_pdu(req);
> +
> + kfree(job->reply);

Don't we need to free the reply-buffer as well?

Not sure how you wanna proceed. I can also sketch something up and
already test it on our cards, to prevent the ping-pong.


Beste Grüße / Best regards,
- Benjamin Block

> +}
> +
> /**
> * bsg_setup_queue - Create and add the bsg hooks so we can receive requests
> * @dev: device to attach bsg device to
> @@ -235,7 +239,9 @@ struct request_queue *bsg_setup_queue(struct device *dev, char *name,
> q = blk_alloc_queue(GFP_KERNEL);
> if (!q)
> return ERR_PTR(-ENOMEM);
> - q->cmd_size = sizeof(struct scsi_request);
> + q->cmd_size = sizeof(struct bsg_job) + dd_job_size;
> + q->init_rq_fn = bsg_init_rq;
> + q->exit_rq_fn = bsg_exit_rq;
> q->request_fn = bsg_request_fn;
>
> ret = blk_init_allocated_queue(q);
> @@ -243,7 +249,6 @@ struct request_queue *bsg_setup_queue(struct device *dev, char *name,
> goto out_cleanup_queue;
>
> q->queuedata = dev;
> - q->bsg_job_size = dd_job_size;
> q->bsg_job_fn = job_fn;
> queue_flag_set_unlocked(QUEUE_FLAG_BIDI, q);
> queue_flag_set_unlocked(QUEUE_FLAG_SCSI_PASSTHROUGH, q);
> diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
> index f45f157b2910..6ae9aa6f93f0 100644
> --- a/include/linux/blkdev.h
> +++ b/include/linux/blkdev.h
> @@ -568,7 +568,6 @@ struct request_queue {
>
> #if defined(CONFIG_BLK_DEV_BSG)
> bsg_job_fn *bsg_job_fn;
> - int bsg_job_size;
> struct bsg_class_device bsg_dev;
> #endif
>
> diff --git a/include/linux/bsg-lib.h b/include/linux/bsg-lib.h
> index e34dde2da0ef..637a20cfb237 100644
> --- a/include/linux/bsg-lib.h
> +++ b/include/linux/bsg-lib.h
> @@ -24,6 +24,7 @@
> #define _BLK_BSG_
>
> #include <linux/blkdev.h>
> +#include <scsi/scsi_request.h>
>
> struct request;
> struct device;
> @@ -37,6 +38,7 @@ struct bsg_buffer {
> };
>
> struct bsg_job {
> + struct scsi_request sreq;
> struct device *dev;
> struct request *req;
>
> --
> 2.11.0
>

--
Linux on z Systems Development / IBM Systems & Technology Group
IBM Deutschland Research & Development GmbH
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