linux-kernel - Re: scsi: BUG in scsi_init

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Date:   Tue, 31 Jan 2017 10:20:48 +0100
From:   Johannes Thumshirn <jthumshirn@...e.de>
To:     Dmitry Vyukov <dvyukov@...gle.com>
Cc:     jejb@...ux.vnet.ibm.com,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        linux-scsi <linux-scsi@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        syzkaller <syzkaller@...glegroups.com>,
        Hannes Reinecke <hare@...e.de>
Subject: Re: scsi: BUG in scsi_init_io

On Tue, Jan 31, 2017 at 09:55:52AM +0100, Dmitry Vyukov wrote:
> Hello,
> 
> The following program triggers BUG in scsi_init_io:

Well crashing a machine just because of an empty dma transfer is a bit harsh,
isn't it?

>From 86e6fa5f618fe588b98e923e032f33e075fcd4f4 Mon Sep 17 00:00:00 2001
From: Johannes Thumshirn <jthumshirn@...e.de>
Date: Tue, 31 Jan 2017 10:16:00 +0100
Subject: [PATCH] scsi: don't BUG_ON() empty DMA transfers

Don't crash the machine just because of an empty transfer. Use WARN_ON()
combined with returning an error.

Signed-off-by: Johannes Thumshirn <jthumshirn@...e.de>
---
 drivers/scsi/scsi_lib.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index e9e1e14..414588a 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -1040,7 +1040,8 @@ int scsi_init_io(struct scsi_cmnd *cmd)
 	bool is_mq = (rq->mq_ctx != NULL);
 	int error;
 
-	BUG_ON(!blk_rq_nr_phys_segments(rq));
+	if (WARN_ON(!blk_rq_nr_phys_segments(rq)))
+		return -EINVAL;
 
 	error = scsi_init_sgtable(rq, &cmd->sdb);
 	if (error)
-- 
2.10.2


-- 
Johannes Thumshirn                                          Storage
jthumshirn@...e.de                                +49 911 74053 689
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