linux-kernel - [PATCH 3.10 014/143] sg: fix dxferp in from

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Message-Id: <1465122046-9645-15-git-send-email-w@1wt.eu>
Date:	Sun,  5 Jun 2016 12:18:37 +0200
From:	Willy Tarreau <w@....eu>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:	Douglas Gilbert <dgilbert@...erlog.com>,
	stable@...r.kernel.org#v2.6.28+,
	"Martin K . Petersen" <martin.petersen@...cle.com>,
	Willy Tarreau <w@....eu>
Subject: [PATCH 3.10 014/143] sg: fix dxferp in from_to case

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.

>From what 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
Cc: <stable@...r.kernel.org> #v2.6.28+
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: Willy Tarreau <w@....eu>
---
 drivers/scsi/sg.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/scsi/sg.c b/drivers/scsi/sg.c
index 0be16bf..1f65e32 100644
--- a/drivers/scsi/sg.c
+++ b/drivers/scsi/sg.c
@@ -633,7 +633,8 @@ sg_write(struct file *filp, const char __user *buf, size_t count, loff_t * ppos)
 	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;
-- 
2.8.0.rc2.1.gbe9624a