ipv4: fib: Move fib_valid_key_len() to rtm_to_fib_config().

fib_valid_key_len() is called in the beginning of fib_table_insert()
or fib_table_delete() to check if the prefix length is valid.

fib_table_insert() and fib_table_delete() are called from 3 paths

  - ip_rt_ioctl()
  - inet_rtm_newroute() / inet_rtm_delroute()
  - fib_magic()

In the first ioctl() path, rtentry_to_fib_config() checks the prefix
length with bad_mask().  Also, fib_magic() always passes the correct
prefix: 32 or ifa->ifa_prefixlen, which is already validated.

Let's move fib_valid_key_len() to the rtnetlink path, rtm_to_fib_config().

While at it, 2 direct returns in rtm_to_fib_config() are changed to
goto to match other places in the same function

Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: David Ahern <dsahern@kernel.org>
Link: https://patch.msgid.link/20250228042328.96624-12-kuniyu@amazon.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

2 files changed, 16 insertions, 24 deletions

diff --git a/net/ipv4/fib_frontend.c b/net/ipv4/fib_frontend.c
index a76dacc3e577..a6372d934e45 100644
--- a/net/ipv4/fib_frontend.c
+++ b/net/ipv4/fib_frontend.c
@@ -835,19 +835,33 @@ static int rtm_to_fib_config(struct net *net, struct sk_buff *skb,
 		}
 	}
 
+	if (cfg->fc_dst_len > 32) {
+		NL_SET_ERR_MSG(extack, "Invalid prefix length");
+		err = -EINVAL;
+		goto errout;
+	}
+
+	if (cfg->fc_dst_len < 32 && (ntohl(cfg->fc_dst) << cfg->fc_dst_len)) {
+		NL_SET_ERR_MSG(extack, "Invalid prefix for given prefix length");
+		err = -EINVAL;
+		goto errout;
+	}
+
 	if (cfg->fc_nh_id) {
 		if (cfg->fc_oif || cfg->fc_gw_family ||
 		    cfg->fc_encap || cfg->fc_mp) {
 			NL_SET_ERR_MSG(extack,
 				       "Nexthop specification and nexthop id are mutually exclusive");
-			return -EINVAL;
+			err = -EINVAL;
+			goto errout;
 		}
 	}
 
 	if (has_gw && has_via) {
 		NL_SET_ERR_MSG(extack,
 			       "Nexthop configuration can not contain both GATEWAY and VIA");
-		return -EINVAL;
+		err = -EINVAL;
+		goto errout;
 	}
 
 	if (!cfg->fc_table)
diff --git a/net/ipv4/fib_trie.c b/net/ipv4/fib_trie.c
index d6411ac81096..59a6f0a9638f 100644
--- a/net/ipv4/fib_trie.c
+++ b/net/ipv4/fib_trie.c
@@ -1187,22 +1187,6 @@ static int fib_insert_alias(struct trie *t, struct key_vector *tp,
 	return 0;
 }
 
-static bool fib_valid_key_len(u32 key, u8 plen, struct netlink_ext_ack *extack)
-{
-	if (plen > KEYLENGTH) {
-		NL_SET_ERR_MSG(extack, "Invalid prefix length");
-		return false;
-	}
-
-	if ((plen < KEYLENGTH) && (key << plen)) {
-		NL_SET_ERR_MSG(extack,
-			       "Invalid prefix for given prefix length");
-		return false;
-	}
-
-	return true;
-}
-
 static void fib_remove_alias(struct trie *t, struct key_vector *tp,
 			     struct key_vector *l, struct fib_alias *old);
 
@@ -1223,9 +1207,6 @@ int fib_table_insert(struct net *net, struct fib_table *tb,
 
 	key = ntohl(cfg->fc_dst);
 
-	if (!fib_valid_key_len(key, plen, extack))
-		return -EINVAL;
-
 	pr_debug("Insert table=%u %08x/%d\n", tb->tb_id, key, plen);
 
 	fi = fib_create_info(cfg, extack);
@@ -1717,9 +1698,6 @@ int fib_table_delete(struct net *net, struct fib_table *tb,
 
 	key = ntohl(cfg->fc_dst);
 
-	if (!fib_valid_key_len(key, plen, extack))
-		return -EINVAL;
-
 	l = fib_find_node(t, &tp, key);
 	if (!l)
 		return -ESRCH;