netdev - [PATCH] net: check negative value for signed refcnt

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Date:   Thu, 31 Jan 2019 14:20:08 +0100
From:   alexandre.besnard@...tathome.com
To:     davem@...emloft.net, ktkhai@...tuozzo.com, ecree@...arflare.com,
        jiri@...lanox.com, petrm@...lanox.com, alexander.h.duyck@...el.com,
        amritha.nambiar@...el.com, lirongqing@...du.com
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        Alexandre Besnard <alexandre.besnard@...tathome.com>
Subject: [PATCH] net: check negative value for signed refcnt

From: Alexandre Besnard <alexandre.besnard@...tathome.com>

Device remaining references counter is get as a signed integer.

When unregistering network devices, the loop waiting for this counter
to decrement tests the 0 strict equality. Thus if an error occurs and
two references are given back by a protocol, we are stuck in the loop
forever, with a -1 value.

Robustness is added by checking a negative value: the device is then
considered free of references, and a warning is issued (it should not
happen, one should check that behavior)

Signed-off-by: Alexandre Besnard <alexandre.besnard@...tathome.com>
---
 net/core/dev.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/net/core/dev.c b/net/core/dev.c
index ddc551f..e4190ae 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -8687,6 +8687,11 @@ static void netdev_wait_allrefs(struct net_device *dev)
 	refcnt = netdev_refcnt_read(dev);

 	while (refcnt != 0) {
+		if (refcnt < 0) {
+			pr_warn("Device %s refcnt negative: device considered free, but it should not happen\n",
+				dev->name);
+			break;
+		}
 		if (time_after(jiffies, rebroadcast_time + 1 * HZ)) {
 			rtnl_lock();

--
2.7.4