Patch "scsi: sg: recheck MMAP_IO request length with lock held" has been added to the 3.18-stable tree

Patch "scsi: sg: recheck MMAP_IO request length with lock held" has been added to the 3.18-stable tree

[gregkh]

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 3.18-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-3.18 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From 8d26f491116feaa0b16de370b6a7ba40a40fa0b4 Mon Sep 17 00:00:00 2001
From: Todd Poynor <toddpoynor@google.com>
Date: Tue, 15 Aug 2017 21:48:43 -0700
Subject: scsi: sg: recheck MMAP_IO request length with lock held

From: Todd Poynor <toddpoynor@google.com>

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.

Signed-off-by: Todd Poynor <toddpoynor@google.com>
Acked-by: Douglas Gilbert <dgilbert@interlog.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

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

--- a/drivers/scsi/sg.c
+++ b/drivers/scsi/sg.c
@@ -1798,9 +1798,12 @@ 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 toddpoynor@google.com are

queue-3.18/scsi-sg-recheck-mmap_io-request-length-with-lock-held.patch
queue-3.18/scsi-sg-protect-against-races-between-mmap-and-sg_set_reserved_size.patch