Patch "Bluetooth: vhci: fix open_timeout vs. hdev race" has been added to the 4.4-stable tree

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

Bluetooth: vhci: fix open_timeout vs. hdev race

to the 4.4-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:
bluetooth-vhci-fix-open_timeout-vs.-hdev-race.patch
and it can be found in the queue-4.4 subdirectory.

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

From: Jiri Slaby <[email protected]>
Date: Sat, 19 Mar 2016 11:05:18 +0100
Subject: Bluetooth: vhci: fix open_timeout vs. hdev race

From: Jiri Slaby <[email protected]>

commit 373a32c848ae3a1c03618517cce85f9211a6facf upstream.

Both vhci_get_user and vhci_release race with open_timeout work. They both contain cancel_delayed_work_sync, but do not test whether the work actually created hdev or not. Since the work can be in progress and _sync will wait for finishing it, we can have data->hdev allocated when cancel_delayed_work_sync returns. But the call sites do 'if (data->hdev)' *before* cancel_delayed_work_sync.

As a result:
* vhci_get_user allocates a second hdev and puts it into data->hdev. The former is leaked.
* vhci_release does not release data->hdev properly as it thinks there is none.

Fix both cases by moving the actual test *after* the call to cancel_delayed_work_sync.

This can be hit by this program:

	#include <err.h>
	#include <fcntl.h>
	#include <stdio.h>
	#include <stdlib.h>
	#include <time.h>
	#include <unistd.h>

	#include <sys/stat.h>
	#include <sys/types.h>

	int main(int argc, char **argv)
	{
		int fd;

		srand(time(NULL));

		while (1) {
			const int delta = (rand() % 200 - 100) * 100;

			fd = open("/dev/vhci", O_RDWR);
			if (fd < 0)
				err(1, "open");

			usleep(1000000 + delta);

			close(fd);
		}

		return 0;
	}

And the result is:

BUG: KASAN: use-after-free in skb_queue_tail+0x13e/0x150 at addr ffff88006b0c1228
Read of size 8 by task kworker/u13:1/32068
=============================================================================

BUG kmalloc-192 (Tainted: G E ): kasan: bad access detected
-----------------------------------------------------------------------------

Disabling lock debugging due to kernel taint
INFO: Allocated in vhci_open+0x50/0x330 [hci_vhci] age=260 cpu=3 pid=32040
...

	kmem_cache_alloc_trace+0x150/0x190
	vhci_open+0x50/0x330 [hci_vhci]
	misc_open+0x35b/0x4e0
	chrdev_open+0x23b/0x510
...
INFO: Freed in vhci_release+0xa4/0xd0 [hci_vhci] age=9 cpu=2 pid=32040
...
	__slab_free+0x204/0x310
	vhci_release+0xa4/0xd0 [hci_vhci]

...
INFO: Slab 0xffffea0001ac3000 objects=16 used=13 fp=0xffff88006b0c1e00 flags=0x5fffff80004080
INFO: Object 0xffff88006b0c1200 @offset=4608 fp=0xffff88006b0c0600
Bytes b4 ffff88006b0c11f0: 09 df 00 00 01 00 00 00 00 00 00 00 00 00 00 00 ................ Object ffff88006b0c1200: 00 06 0c 6b 00 88 ff ff 00 00 00 00 00 00 00 00 ...k............ Object ffff88006b0c1210: 10 12 0c 6b 00 88 ff ff 10 12 0c 6b 00 88 ff ff ...k.......k.... Object ffff88006b0c1220: c0 46 c2 6b 00 88 ff ff c0 46 c2 6b 00 88 ff ff .F.k.....F.k.... Object ffff88006b0c1230: 01 00 00 00 01 00 00 00 e0 ff ff ff 0f 00 00 00 ................ Object ffff88006b0c1240: 40 12 0c 6b 00 88 ff ff 40 12 0c 6b 00 88 ff ff @[email protected].... Object ffff88006b0c1250: 50 0d 6e a0 ff ff ff ff 00 02 00 00 00 00 ad de P.n............. Object ffff88006b0c1260: 00 00 00 00 00 00 00 00 ab 62 02 00 01 00 00 00 .........b...... Object ffff88006b0c1270: 90 b9 19 81 ff ff ff ff 38 12 0c 6b 00 88 ff ff ........8..k.... Object ffff88006b0c1280: 03 00 20 00 ff ff ff ff ff ff ff ff 00 00 00 00 .. ............. Object ffff88006b0c1290: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ Object ffff88006b0c12a0: 00 00 00 00 00 00 00 00 00 80 cd 3d 00 88 ff ff ...........=.... Object ffff88006b0c12b0: 00 20 00 00 00 00 00 00 00 00 00 00 00 00 00 00 . ..............
Redzone ffff88006b0c12c0: bb bb bb bb bb bb bb bb ........
Padding ffff88006b0c13f8: 00 00 00 00 00 00 00 00 ........

CPU: 3 PID: 32068 Comm: kworker/u13:1 Tainted: G    B       E      4.4.6-0-default #1
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.8.1-0-g4adadbd-20151112_172657-sheep25 04/01/2014
Workqueue: hci0 hci_cmd_work [bluetooth]
 00000000ffffffff ffffffff81926cfa ffff88006be37c68 ffff88006bc27180
 ffff88006b0c1200 ffff88006b0c1234 ffffffff81577993 ffffffff82489320
 ffff88006bc24240 0000000000000046 ffff88006a100000 000000026e51eb80
Call Trace:

...
[<ffffffff81ec8ebe>] ? skb_queue_tail+0x13e/0x150 [<ffffffffa06e027c>] ? vhci_send_frame+0xac/0x100 [hci_vhci] [<ffffffffa0c61268>] ? hci_send_frame+0x188/0x320 [bluetooth] [<ffffffffa0c61515>] ? hci_cmd_work+0x115/0x310 [bluetooth] [<ffffffff811a1375>] ? process_one_work+0x815/0x1340 [<ffffffff811a1f85>] ? worker_thread+0xe5/0x11f0 [<ffffffff811a1ea0>] ? process_one_work+0x1340/0x1340 [<ffffffff811b3c68>] ? kthread+0x1c8/0x230
...

Memory state around the buggy address:
 ffff88006b0c1100: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff88006b0c1180: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff88006b0c1200: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                                  ^
 ffff88006b0c1280: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
 ffff88006b0c1300: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc

---
 drivers/bluetooth/hci_vhci.c |    8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

@@ -189,13 +189,13 @@ static inline ssize_t vhci_get_user(stru
 		break;
 
 	case HCI_VENDOR_PKT:
+		cancel_delayed_work_sync(&data->open_timeout);
+
 		if (data->hdev) {
 			kfree_skb(skb);
 			return -EBADFD;
 		}
 
-		cancel_delayed_work_sync(&data->open_timeout);
-
 		opcode = *((__u8 *) skb->data);
 		skb_pull(skb, 1);
 

@@ -333,10 +333,12 @@ static int vhci_open(struct inode *inode
 static int vhci_release(struct inode *inode, struct file *file)
 {
 	struct vhci_data *data = file->private_data;
-	struct hci_dev *hdev = data->hdev;
+	struct hci_dev *hdev;
 
 	cancel_delayed_work_sync(&data->open_timeout);
 
+	hdev = data->hdev;
+
 	if (hdev) {
 		hci_unregister_dev(hdev);
 		hci_free_dev(hdev);

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

queue-4.4/bluetooth-vhci-purge-unhandled-skbs.patch queue-4.4/bluetooth-vhci-fix-open_timeout-vs.-hdev-race.patch