[PATCH 1/2] net: mac80211: Fix possible null-pointer dereferences in ieee80211_setup_sdata()

[PATCH 1/2] net: mac80211: Fix possible null-pointer dereferences in ieee80211_setup_sdata()

[Jia-Ju Bai]

In ieee80211_setup_sdata(), there is an if statement on line 1410 to
check whether sdata->dev is NULL:
    if (sdata->dev)

When sdata->dev is NULL, it is used on lines 1458 and 1459:
    sdata->dev->type = ARPHRD_IEEE80211_RADIOTAP;
    sdata->dev->netdev_ops = &ieee80211_monitorif_ops;

Thus, possible null-pointer dereferences may occur.

To fix these bugs, sdata->dev is checked before being used.

These bugs are found by a static analysis tool STCheck written by us.

Signed-off-by: Jia-Ju Bai <baijiaju1990@gmail.com>
---
 net/mac80211/iface.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/net/mac80211/iface.c b/net/mac80211/iface.c
index 06aac0aaae64..e49264981a7b 100644
--- a/net/mac80211/iface.c
+++ b/net/mac80211/iface.c
@@ -1455,8 +1455,10 @@ static void ieee80211_setup_sdata(struct ieee80211_sub_if_data *sdata,
 			ieee80211_mesh_init_sdata(sdata);
 		break;
 	case NL80211_IFTYPE_MONITOR:
-		sdata->dev->type = ARPHRD_IEEE80211_RADIOTAP;
-		sdata->dev->netdev_ops = &ieee80211_monitorif_ops;
+		if (sdata->dev) {
+			sdata->dev->type = ARPHRD_IEEE80211_RADIOTAP;
+			sdata->dev->netdev_ops = &ieee80211_monitorif_ops;
+		}
 		sdata->u.mntr.flags = MONITOR_FLAG_CONTROL |
 				      MONITOR_FLAG_OTHER_BSS;
 		break;
-- 
2.17.0

Re: [PATCH 1/2] net: mac80211: Fix possible null-pointer dereferences in ieee80211_setup_sdata()

[Johannes Berg]

On Wed, 2019-07-24 at 20:36 +0800, Jia-Ju Bai wrote:
> In ieee80211_setup_sdata(), there is an if statement on line 1410 to
> check whether sdata->dev is NULL:
>     if (sdata->dev)
> 
> When sdata->dev is NULL, it is used on lines 1458 and 1459:
>     sdata->dev->type = ARPHRD_IEEE80211_RADIOTAP;
>     sdata->dev->netdev_ops = &ieee80211_monitorif_ops;
> 
> Thus, possible null-pointer dereferences may occur.

No, this cannot happen, monitor interfaces (NL80211_IFTYPE_MONITOR) must
have a valid ->dev, only P2P device and NAN might not.

johannes