ipv4: Check attribute length for RTA_GATEWAY in multipath route

syzbot reported uninit-value:
============================================================
  BUG: KMSAN: uninit-value in fib_get_nhs+0xac4/0x1f80
  net/ipv4/fib_semantics.c:708
   fib_get_nhs+0xac4/0x1f80 net/ipv4/fib_semantics.c:708
   fib_create_info+0x2411/0x4870 net/ipv4/fib_semantics.c:1453
   fib_table_insert+0x45c/0x3a10 net/ipv4/fib_trie.c:1224
   inet_rtm_newroute+0x289/0x420 net/ipv4/fib_frontend.c:886

Add helper to validate RTA_GATEWAY length before using the attribute.

Fixes: 4e902c57417c ("[IPv4]: FIB configuration using struct fib_config")
Reported-by: syzbot+d4b9a2851cc3ce998741@syzkaller.appspotmail.com
Signed-off-by: David Ahern <dsahern@kernel.org>
Cc: Thomas Graf <tgraf@suug.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/ipv4/fib_semantics.c b/net/ipv4/fib_semantics.c
index fde7797..f1caa2c 100644 (file)
--- a/net/ipv4/fib_semantics.c
+++ b/net/ipv4/fib_semantics.c
@@ -662,6 +662,19 @@ static int fib_count_nexthops(struct rtnexthop *rtnh, int remaining,
        return nhs;
 }
 
+static int fib_gw_from_attr(__be32 *gw, struct nlattr *nla,
+                           struct netlink_ext_ack *extack)
+{
+       if (nla_len(nla) < sizeof(*gw)) {
+               NL_SET_ERR_MSG(extack, "Invalid IPv4 address in RTA_GATEWAY");
+               return -EINVAL;
+       }
+
+       *gw = nla_get_in_addr(nla);
+
+       return 0;
+}
+
 /* only called when fib_nh is integrated into fib_info */
 static int fib_get_nhs(struct fib_info *fi, struct rtnexthop *rtnh,
                       int remaining, struct fib_config *cfg,
@@ -704,7 +717,11 @@ static int fib_get_nhs(struct fib_info *fi, struct rtnexthop *rtnh,
                                return -EINVAL;
                        }
                        if (nla) {
-                               fib_cfg.fc_gw4 = nla_get_in_addr(nla);
+                               ret = fib_gw_from_attr(&fib_cfg.fc_gw4, nla,
+                                                      extack);
+                               if (ret)
+                                       goto errout;
+
                                if (fib_cfg.fc_gw4)
                                        fib_cfg.fc_gw_family = AF_INET;
                        } else if (nlav) {
@@ -902,6 +919,7 @@ int fib_nh_match(struct net *net, struct fib_config *cfg, struct fib_info *fi,
                attrlen = rtnh_attrlen(rtnh);
                if (attrlen > 0) {
                        struct nlattr *nla, *nlav, *attrs = rtnh_attrs(rtnh);
+                       int err;
 
                        nla = nla_find(attrs, attrlen, RTA_GATEWAY);
                        nlav = nla_find(attrs, attrlen, RTA_VIA);
@@ -912,12 +930,17 @@ int fib_nh_match(struct net *net, struct fib_config *cfg, struct fib_info *fi,
                        }
 
                        if (nla) {
+                               __be32 gw;
+
+                               err = fib_gw_from_attr(&gw, nla, extack);
+                               if (err)
+                                       return err;
+
                                if (nh->fib_nh_gw_family != AF_INET ||
-                                   nla_get_in_addr(nla) != nh->fib_nh_gw4)
+                                   gw != nh->fib_nh_gw4)
                                        return 1;
                        } else if (nlav) {
                                struct fib_config cfg2;
-                               int err;
 
                                err = fib_gw_from_via(&cfg2, nlav, extack);
                                if (err)