Patch "net: phy: Fix lack of reference count on PHY driver" has been added to the 4.9-stable tree

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

net: phy: Fix lack of reference count on PHY driver

to the 4.9-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:
net-phy-fix-lack-of-reference-count-on-phy-driver.patch
and it can be found in the queue-4.9 subdirectory.

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

From: Mao Wenan <[email protected]>
Date: Tue, 23 May 2017 21:54:00 -0400
Subject: net: phy: Fix lack of reference count on PHY driver

From: Mao Wenan <[email protected]>

[ Upstream commit cafe8df8b9bc9aa3dffa827c1a6757c6cd36f657 ]

There is currently no reference count being held on the PHY driver, which makes it possible to remove the PHY driver module while the PHY state machine is running and polling the PHY. This could cause crashes similar to this one to show up:

[   43.361162] BUG: unable to handle kernel NULL pointer dereference at 0000000000000140
[   43.361162] IP: phy_state_machine+0x32/0x490
[   43.361162] PGD 59dc067
[   43.361162] PUD 0
[   43.361162]
[   43.361162] Oops: 0000 [#1] SMP
[   43.361162] Modules linked in: dsa_loop [last unloaded: broadcom]
[   43.361162] CPU: 0 PID: 1299 Comm: kworker/0:3 Not tainted 4.10.0-rc5+ #415
[   43.361162] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996),
BIOS Ubuntu-1.8.2-1ubuntu2 04/01/2014
[   43.361162] Workqueue: events_power_efficient phy_state_machine
[   43.361162] task: ffff880006782b80 task.stack: ffffc90000184000
[   43.361162] RIP: 0010:phy_state_machine+0x32/0x490
[   43.361162] RSP: 0018:ffffc90000187e18 EFLAGS: 00000246
[   43.361162] RAX: 0000000000000000 RBX: ffff8800059e53c0 RCX:
ffff880006a15c60
[   43.361162] RDX: ffff880006782b80 RSI: 0000000000000000 RDI:
ffff8800059e5428
[   43.361162] RBP: ffffc90000187e48 R08: ffff880006a15c40 R09:
0000000000000000
[   43.361162] R10: 0000000000000000 R11: 0000000000000000 R12:
ffff8800059e5428
[   43.361162] R13: ffff8800059e5000 R14: 0000000000000000 R15:
ffff880006a15c40
[   43.361162] FS:  0000000000000000(0000) GS:ffff880006a00000(0000)
knlGS:0000000000000000
[   43.361162] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   43.361162] CR2: 0000000000000140 CR3: 0000000005979000 CR4:
00000000000006f0
[   43.361162] Call Trace:
[   43.361162]  process_one_work+0x1b4/0x3e0
[   43.361162]  worker_thread+0x43/0x4d0
[   43.361162]  ? __schedule+0x17f/0x4e0
[   43.361162]  kthread+0xf7/0x130
[   43.361162]  ? process_one_work+0x3e0/0x3e0
[   43.361162]  ? kthread_create_on_node+0x40/0x40
[   43.361162]  ret_from_fork+0x29/0x40
[   43.361162] Code: 56 41 55 41 54 4c 8d 67 68 53 4c 8d af 40 fc ff ff

48 89 fb 4c 89 e7 48 83 ec 08 e8 c9 9d 27 00 48 8b 83 60 ff ff ff 44 8b 73 98 <48> 8b 90 40 01 00 00 44 89 f0 48 85 d2 74 08 4c 89 ef ff d2 8b

Keep references on the PHY driver module right before we are going to utilize it in phy_attach_direct(), and conversely when we don't use it anymore in phy_detach().

---
 drivers/net/phy/phy_device.c |    7 +++++++
 1 file changed, 7 insertions(+)

@@ -872,6 +872,11 @@ int phy_attach_direct(struct net_device
 		return -EIO;
 	}
 
+	if (!try_module_get(d->driver->owner)) {
+		dev_err(&dev->dev, "failed to get the device driver module\n");
+		return -EIO;
+	}
+
 	get_device(d);
 
 	/* Assume that if there is no driver, that it doesn't

@@ -927,6 +932,7 @@ int phy_attach_direct(struct net_device
 
 error:
 	put_device(d);
+	module_put(d->driver->owner);
 	if (ndev_owner != bus->owner)
 		module_put(bus->owner);
 	return err;

@@ -1007,6 +1013,7 @@ void phy_detach(struct phy_device *phyde
 	bus = phydev->mdio.bus;
 
 	put_device(&phydev->mdio.dev);
+	module_put(phydev->mdio.dev.driver->owner);
 	if (ndev_owner != bus->owner)
 		module_put(bus->owner);
 }

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

queue-4.9/net-phy-fix-lack-of-reference-count-on-phy-driver.patch