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Subject[PATCH 3.2 026/115] sg: fix dxferp in from_to case
3.2.80-rc1 review patch.  If anyone has any objections, please let me know.

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

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

--- a/drivers/scsi/sg.c
+++ b/drivers/scsi/sg.c
@@ -609,7 +609,8 @@ 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;
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