linux-kernel - [PATCH 3.16 086/217] sg: fix dxferp in from

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Date:	Wed, 27 Apr 2016 01:02:21 +0200
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:	akpm@...ux-foundation.org,
	"Martin K. Petersen" <martin.petersen@...cle.com>,
	"Ewan Milne" <emilne@...hat.com>,
	"Douglas Gilbert" <dgilbert@...erlog.com>
Subject: [PATCH 3.16 086/217] sg: fix dxferp in from_to case

3.16.35-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Douglas Gilbert <dgilbert@...erlog.com>

commit 5ecee0a3ee8d74b6950cb41e8989b0c2174568d4 upstream.

One of the strange things that the original sg driver did was let the
user provide both a data-out buffer (it followed the sg_header+cdb)
_and_ specify a reply length greater than zero. What happened was that
the user data-out buffer was copied into some kernel buffers and then
the mid level was told a read type operation would take place with the
data from the device overwriting the same kernel buffers. The user would
then read those kernel buffers back into the user space.

=46romwhat I can tell, the above action was broken by commit fad7f01e61bf
("sg: set dxferp to NULL for READ with the older SG interface") in 2008
and syzkaller found that out recently.

Make sure that a user space pointer is passed through when data follows
the sg_header structure and command.  Fix the abnormal case when a
non-zero reply_len is also given.

Fixes: fad7f01e61bf737fe8a3740d803f000db57ecac6
Signed-off-by: Douglas Gilbert <dgilbert@...erlog.com>
Reviewed-by: Ewan Milne <emilne@...hat.com>
Signed-off-by: Martin K. Petersen <martin.petersen@...cle.com>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 drivers/scsi/sg.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/drivers/scsi/sg.c
+++ b/drivers/scsi/sg.c
@@ -633,7 +633,8 @@ sg_write(struct file *filp, const char _
 	else
 		hp->dxfer_direction = (mxsize > 0) ? SG_DXFER_FROM_DEV : SG_DXFER_NONE;
 	hp->dxfer_len = mxsize;
-	if (hp->dxfer_direction == SG_DXFER_TO_DEV)
+	if ((hp->dxfer_direction == SG_DXFER_TO_DEV) ||
+	    (hp->dxfer_direction == SG_DXFER_TO_FROM_DEV))
 		hp->dxferp = (char __user *)buf + cmd_size;
 	else
 		hp->dxferp = NULL;