[PATCH v1] rtnetlink: let rtnl_bridge_setlink checks IFLA_BRIDGE_MODE length

[Lin Ma]

There are totally 9 ndo_bridge_setlink handlers in the current kernel,
which are 1) bnxt_bridge_setlink, 2) be_ndo_bridge_setlink 3)
i40e_ndo_bridge_setlink 4) ice_bridge_setlink 5)
ixgbe_ndo_bridge_setlink 6) mlx5e_bridge_setlink 7)
nfp_net_bridge_setlink 8) qeth_l2_bridge_setlink 9) br_setlink.

By investigating the code, we find that 1-7 parse and use nlattr
IFLA_BRIDGE_MODE but 3 and 4 forget to do the nla_len check. This can
lead to an out-of-attribute read and allow a malformed nlattr (e.g.,
length 0) to be viewed as a 2 byte integer.

To avoid such issues, also for other ndo_bridge_setlink handlers in the
future. This patch adds the nla_len check in rtnl_bridge_setlink and
does an early error return if length mismatches.

Fixes: b1edc14a3fbf ("ice: Implement ice_bridge_getlink and ice_bridge_setlink")
Fixes: 51616018dd1b ("i40e: Add support for getlink, setlink ndo ops")
Suggested-by: Jakub Kicinski <kuba@xxxxxxxxxx>
Signed-off-by: Lin Ma <linma@xxxxxxxxxx>
---
 net/core/rtnetlink.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
index 3ad4e030846d..1e51291007ea 100644
--- a/net/core/rtnetlink.c
+++ b/net/core/rtnetlink.c
@@ -5148,6 +5148,11 @@ static int rtnl_bridge_setlink(struct sk_buff *skb, struct nlmsghdr *nlh,
 				flags = nla_get_u16(attr);
 				break;
 			}
+
+			if (nla_type(attr) == IFLA_BRIDGE_MODE) {
+				if (nla_len(attr) < sizeof(u16))
+					return -EINVAL;
+			}
 		}
 	}
 
-- 
2.17.1