netdev - [PATCH net] net: ipconfig: ic_dev can be NULL in ic_close

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Date:   Mon, 22 Mar 2021 02:26:37 +0200
From:   Vladimir Oltean <olteanv@...il.com>
To:     "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>, netdev@...r.kernel.org
Cc:     Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        David Ahern <dsahern@...nel.org>,
        Florian Fainelli <f.fainelli@...il.com>,
        Andrew Lunn <andrew@...n.ch>,
        Vladimir Oltean <vladimir.oltean@....com>
Subject: [PATCH net] net: ipconfig: ic_dev can be NULL in ic_close_devs

From: Vladimir Oltean <vladimir.oltean@....com>

ic_close_dev contains a generalization of the logic to not close a
network interface if it's the host port for a DSA switch. This logic is
disguised behind an iteration through the lowers of ic_dev in
ic_close_dev.

When no interface for ipconfig can be found, ic_dev is NULL, and
ic_close_dev:
- dereferences a NULL pointer when assigning selected_dev
- would attempt to search through the lower interfaces of a NULL
  net_device pointer

So we should protect against that case.

The "lower_dev" iterator variable was shortened to "lower" in order to
keep the 80 character limit.

Fixes: f68cbaed67cb ("net: ipconfig: avoid use-after-free in ic_close_devs")
Fixes: 46acf7bdbc72 ("Revert "net: ipv4: handle DSA enabled master network devices"")
Signed-off-by: Vladimir Oltean <vladimir.oltean@....com>
---
 net/ipv4/ipconfig.c | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/net/ipv4/ipconfig.c b/net/ipv4/ipconfig.c
index 47db1bfdaaa0..bc2f6ca97152 100644
--- a/net/ipv4/ipconfig.c
+++ b/net/ipv4/ipconfig.c
@@ -309,7 +309,7 @@ static int __init ic_open_devs(void)
  */
 static void __init ic_close_devs(void)
 {
-	struct net_device *selected_dev = ic_dev->dev;
+	struct net_device *selected_dev = ic_dev ? ic_dev->dev : NULL;
 	struct ic_device *d, *next;
 	struct net_device *dev;
 
@@ -317,16 +317,18 @@ static void __init ic_close_devs(void)
 	next = ic_first_dev;
 	while ((d = next)) {
 		bool bring_down = (d != ic_dev);
-		struct net_device *lower_dev;
+		struct net_device *lower;
 		struct list_head *iter;
 
 		next = d->next;
 		dev = d->dev;
 
-		netdev_for_each_lower_dev(selected_dev, lower_dev, iter) {
-			if (dev == lower_dev) {
-				bring_down = false;
-				break;
+		if (selected_dev) {
+			netdev_for_each_lower_dev(selected_dev, lower, iter) {
+				if (dev == lower) {
+					bring_down = false;
+					break;
+				}
 			}
 		}
 		if (bring_down) {
-- 
2.25.1