[SCSI] sg: Free data buffers after calling blk_rq_unmap_user

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@lab.ntt.co.jp>
Cc: stable@kernel.org
Signed-off-by: Christof Schmitt <christof.schmitt@de.ibm.com>
Acked-by: Douglas Gilbert <dgilbert@interlog.com>
Signed-off-by: James Bottomley <James.Bottomley@suse.de>

1 files changed, 5 insertions, 5 deletions

diff --git a/drivers/scsi/sg.c b/drivers/scsi/sg.c
index 0cb049f5cc56..a328b5f284de 100644
--- a/drivers/scsi/sg.c
+++ b/drivers/scsi/sg.c
@@ -1708,11 +1708,6 @@ static int sg_finish_rem_req(Sg_request * srp)
         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 * srp)
                 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;