[03/46] SCSI: sg: Free data buffers after calling blk_rq_unmap_user

[Greg KH]

2.6.31-stable review patch.  If anyone has any objections, please let us know.

------------------
From: Christof Schmitt <christof.schmitt@xxxxxxxxxx>

commit e27168f8c337b12b8aa8d59c3123c79d2f83603d upstream.

Running sg_luns on s390x with CONFIG_DEBUG_PAGEALLOC enabled fails
with EFAULT from the SG_IO ioctl. The EFAULT is the result from
copy_to_user failing in this call chain:

sg_ioctl
sg_new_read
sg_finish_rem_req
blk_rq_unmap_user
__blk_rq_unmap_user
bio_uncopy_user
__bio_copy_iov
copy_to_user

The sg driver calls sg_remove_scat to free the memory pages before
calling blk_rq_unmap_user that tries to copy the data back to
userspace. Change the order to first call blk_rq_unmap_user before
freeing the pages in sg_remove_scat.

Acked-by: FUJITA Tomonori <fujita.tomonori@xxxxxxxxxxxxx>
Signed-off-by: Christof Schmitt <christof.schmitt@xxxxxxxxxx>
Acked-by: Douglas Gilbert <dgilbert@xxxxxxxxxxxx>
Signed-off-by: James Bottomley <James.Bottomley@xxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxx>

---
 drivers/scsi/sg.c |   10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

--- a/drivers/scsi/sg.c
+++ b/drivers/scsi/sg.c
@@ -1708,11 +1708,6 @@ static int sg_finish_rem_req(Sg_request 
 	Sg_scatter_hold *req_schp = &srp->data;
 
 	SCSI_LOG_TIMEOUT(4, printk("sg_finish_rem_req: res_used=%d\n", (int) srp->res_used));
-	if (srp->res_used)
-		sg_unlink_reserve(sfp, srp);
-	else
-		sg_remove_scat(req_schp);
-
 	if (srp->rq) {
 		if (srp->bio)
 			ret = blk_rq_unmap_user(srp->bio);
@@ -1720,6 +1715,11 @@ static int sg_finish_rem_req(Sg_request 
 		blk_put_request(srp->rq);
 	}
 
+	if (srp->res_used)
+		sg_unlink_reserve(sfp, srp);
+	else
+		sg_remove_scat(req_schp);
+
 	sg_remove_request(sfp, srp);
 
 	return ret;


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