Patch "skd: Avoid that module unloading triggers a use-after-free" has been added to the 3.18-stable tree

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

skd: Avoid that module unloading triggers a use-after-free

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:
skd-avoid-that-module-unloading-triggers-a-use-after-free.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 <[email protected]> know about it.

From: Bart Van Assche <[email protected]>
Date: Thu, 17 Aug 2017 13:12:45 -0700
Subject: skd: Avoid that module unloading triggers a use-after-free

From: Bart Van Assche <[email protected]>

commit 7277cc67b3916eed47558c64f9c9c0de00a35cda upstream.

Since put_disk() triggers a disk_release() call and since that last function calls blk_put_queue() if disk->queue != NULL, clear the disk->queue pointer before calling put_disk(). This avoids that unloading the skd kernel module triggers the following use-after-free:

WARNING: CPU: 8 PID: 297 at lib/refcount.c:128 refcount_sub_and_test+0x70/0x80
refcount_t: underflow; use-after-free.
CPU: 8 PID: 297 Comm: kworker/8:1 Not tainted 4.11.10-300.fc26.x86_64 #1
Workqueue: events work_for_cpu_fn
Call Trace:
 dump_stack+0x63/0x84
 __warn+0xcb/0xf0
 warn_slowpath_fmt+0x5a/0x80
 refcount_sub_and_test+0x70/0x80
 refcount_dec_and_test+0x11/0x20
 kobject_put+0x1f/0x50
 blk_put_queue+0x15/0x20
 disk_release+0xae/0xf0
 device_release+0x32/0x90
 kobject_release+0x67/0x170
 kobject_put+0x2b/0x50
 put_disk+0x17/0x20
 skd_destruct+0x5c/0x890 [skd]
 skd_pci_probe+0x124d/0x13a0 [skd]
 local_pci_probe+0x42/0xa0
 work_for_cpu_fn+0x14/0x20
 process_one_work+0x19e/0x470
 worker_thread+0x1dc/0x4a0
 kthread+0x125/0x140
 ret_from_fork+0x25/0x30

---
 drivers/block/skd_main.c |   15 ++++++++-------
 1 file changed, 8 insertions(+), 7 deletions(-)

@@ -4679,15 +4679,16 @@ static void skd_free_disk(struct skd_dev
 {
 	struct gendisk *disk = skdev->disk;
 
-	if (disk != NULL) {
-		struct request_queue *q = disk->queue;
+	if (disk && (disk->flags & GENHD_FL_UP))
+		del_gendisk(disk);
 
-		if (disk->flags & GENHD_FL_UP)
-			del_gendisk(disk);
-		if (q)
-			blk_cleanup_queue(q);
-		put_disk(disk);
+	if (skdev->queue) {
+		blk_cleanup_queue(skdev->queue);
+		skdev->queue = NULL;
+		disk->queue = NULL;
 	}
+
+	put_disk(disk);
 	skdev->disk = NULL;
 }
 

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

queue-3.18/skd-submit-requests-to-firmware-before-triggering-the-doorbell.patch queue-3.18/block-relax-a-check-in-blk_start_queue.patch queue-3.18/skd-avoid-that-module-unloading-triggers-a-use-after-free.patch