linux-kernel - Re: Re: [Patch] bsg: initialize request and reply payloads in bsg_prepare

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Message-ID: <20260206045850epcms2p2b10bcfd30a1c768fb35b2994b29454de@epcms2p2>
Date: Fri, 06 Feb 2026 13:58:50 +0900
From: 라종휘 <jonghwi.rha@...sung.com>
To: Hannes Reinecke <hare@...e.de>, Jens Axboe <axboe@...nel.dk>
CC: "linux-block@...r.kernel.org" <linux-block@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "hch@....de"
	<hch@....de>, 김정태 <jt1217.kim@...sung.com>,
	정혜연 <hyeon.chung@...sung.com>
Subject: Re: Re: [Patch] bsg: initialize request and reply payloads in
 bsg_prepare_job

On 2/6/26 00:45, Hannes Reinecke wrote:
> On 2/5/26 14:42, Jens Axboe wrote:
>> On 2/4/26 10:32 PM, ??? wrote:
>>> bsg: initialize request and reply payloads in bsg_prepare_job
>>>
>>> struct bsg_job payloads contain fields that are only populated by
>>> certain commands, such as sg_list pointers.
>>>
>>> Because struct bsg_job is allocated with kmalloc(), memory may be
>>> reused across requests. If a command does not populate all payload
>>> fields, stale state from a previous job may remain and later be
>>> misinterpreted during cleanup, potentially leading to use-after-free
>>> or double-free issues.
>>>
>>> Initialize both request and reply payloads at the beginning of job
>>> preparation to ensure a clean state for all commands.
>>>
>>> Signed-off-by: Jonghwi Rha <jonghwi.rha@...sung.com>
>>>
>>> diff --git a/block/bsg-lib.c b/block/bsg-lib.c
>>> index 32da4a4429ce..0fbf8e311c03 100644
>>> --- a/block/bsg-lib.c
>>> +++ b/block/bsg-lib.c
>>> @@ -234,6 +234,12 @@ static bool bsg_prepare_job(struct device *dev, struct request *req)
>>>          struct bsg_job *job = blk_mq_rq_to_pdu(req);
>>>          int ret;
>>>
>>> +      /* Clear stale SG state since bsg_job is reused as a request PDU */
>>> +      job->request_payload.sg_list = NULL;
>>> +      job->request_payload.sg_cnt = 0;
>>> +      job->reply_payload.sg_list = NULL;
>>> +      job->reply_payload.sg_cnt = 0;
>>> +
>>>          job->timeout = req->timeout;
>>>
>>>          if (req->bio) {
>>
>> The patch is white-space damaged, tabs are spaces. But I can fix that
>> up. Do we just want to do a memset(job, 0, sizeof(*job)) here to avoid
>> any oddities like this in the future?
>>
>
> That might indeed be better.

The suggested method impairs normal operation. If bsg_prepare_job performs a zero‑memset for the job structure, all request‑related information set on the driver side before the call will be lost. Therefore, if it runs as is, it will go to ufs_bsg_request and cause a null‑pointer access.

Currently, the original patch has no functional impact.

The blank problem seems to be due to a mistake I made while copying and pasting the patch. I am reattaching the patch below. If needed, I can attach the patch and resend the new email.


[PATCH] bsg: initialize request and reply payloads in bsg_prepare_job

struct bsg_job payloads contain fields that are only populated by
certain commands, such as sg_list pointers.

Because struct bsg_job is allocated with kmalloc(), memory may be
reused across requests. If a command does not populate all payload
fields, stale state from a previous job may remain and later be
misinterpreted during cleanup, potentially leading to use-after-free
or double-free issues.

Initialize both request and reply payloads at the beginning of job
preparation to ensure a clean state for all commands.

Signed-off-by: Jonghwi Rha <jonghwi.rha@...sung.com>
---
 block/bsg-lib.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/block/bsg-lib.c b/block/bsg-lib.c
index 32da4a4429ce..0fbf8e311c03 100644
--- a/block/bsg-lib.c
+++ b/block/bsg-lib.c
@@ -234,6 +234,12 @@ static bool bsg_prepare_job(struct device *dev, struct request *req)
 	struct bsg_job *job = blk_mq_rq_to_pdu(req);
 	int ret;
 
+	/* Clear stale SG state since bsg_job is reused as a request PDU */
+	job->request_payload.sg_list = NULL;
+	job->request_payload.sg_cnt = 0;
+	job->reply_payload.sg_list = NULL;
+	job->reply_payload.sg_cnt = 0;
+
 	job->timeout = req->timeout;
 
 	if (req->bio) {
-- 

Regards,
Jonghwi,