sg: fix dxferp in from_to case

[ Upstream commit 5ecee0a3ee8d74b6950cb41e8989b0c2174568d4 ]

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@vger.kernel.org> #v2.6.28+
Signed-off-by: Douglas Gilbert <dgilbert@interlog.com>
Reviewed-by: Ewan Milne <emilne@redhat.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Sasha Levin <sasha.levin@oracle.com>

diff --git a/drivers/scsi/sg.c b/drivers/scsi/sg.c
index a1866c0c6a57e6b2d0a24e5d09163b1765d03539..bc09f1d196c9ecd0ba4c9d8a78993e46a423e0c6 100644 (file)
--- a/drivers/scsi/sg.c
+++ b/drivers/scsi/sg.c
@@ -652,7 +652,8 @@ 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;