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sg: fix dxferp in from_to case 

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 fad7f01e61
("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: fad7f01e61
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>
This commit is contained in:
Douglas Gilbert 2016-03-03 00:31:29 -05:00 committed by Martin K. Petersen
parent ff06c5ffbc
commit 5ecee0a3ee
1 changed files with 2 additions and 1 deletions
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3
drivers/scsi/sg.c
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@ -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;