Patch "scsi: sg: recheck MMAP_IO request length with lock held" has been added to the 4.13-stable tree

This is a note to let you know that I've just added the patch titled

scsi: sg: recheck MMAP_IO request length with lock held

to the 4.13-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
scsi-sg-recheck-mmap_io-request-length-with-lock-held.patch
and it can be found in the queue-4.13 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Todd Poynor <[email protected]>
Date: Tue, 15 Aug 2017 21:48:43 -0700
Subject: scsi: sg: recheck MMAP_IO request length with lock held

From: Todd Poynor <[email protected]>

commit 8d26f491116feaa0b16de370b6a7ba40a40fa0b4 upstream.

Commit 1bc0eb044615 ("scsi: sg: protect accesses to 'reserved' page array") adds needed concurrency protection for the "reserve" buffer. Some checks that are initially made outside the lock are replicated once the lock is taken to ensure the checks and resulting decisions are made using consistent state.

The check that a request with flag SG_FLAG_MMAP_IO set fits in the reserve buffer also needs to be performed again under the lock to ensure the reserve buffer length compared against matches the value in effect when the request is linked to the reserve buffer. An -ENOMEM should be returned in this case, instead of switching over to an indirect buffer as for non-MMAP_IO requests.

---
 drivers/scsi/sg.c |    7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

@@ -1741,9 +1741,12 @@ sg_start_req(Sg_request *srp, unsigned c
 		    !sfp->res_in_use) {
 			sfp->res_in_use = 1;
 			sg_link_reserve(sfp, srp, dxfer_len);
-		} else if ((hp->flags & SG_FLAG_MMAP_IO) && sfp->res_in_use) {
+		} else if (hp->flags & SG_FLAG_MMAP_IO) {
+			res = -EBUSY; /* sfp->res_in_use == 1 */
+			if (dxfer_len > rsv_schp->bufflen)
+				res = -ENOMEM;
 			mutex_unlock(&sfp->f_mutex);
-			return -EBUSY;
+			return res;
 		} else {
 			res = sg_build_indirect(req_schp, sfp, dxfer_len);
 			if (res) {

Patches currently in stable-queue which might be from [email protected] are

queue-4.13/scsi-sg-recheck-mmap_io-request-length-with-lock-held.patch queue-4.13/scsi-sg-protect-against-races-between-mmap-and-sg_set_reserved_size.patch