esp4: add length check for UDP encapsulation

esp_output_udp_encap can produce a length that doesn't fit in the 16
bits of a UDP header's length field. In that case, we'll send a
fragmented packet whose length is larger than IP_MAX_MTU (resulting in
"Oversized IP packet" warnings on receive) and with a bogus UDP
length.

To prevent this, add a length check to esp_output_udp_encap and return
 -EMSGSIZE on failure.

This seems to be older than git history.

Signed-off-by: Sabrina Dubroca <sd@queasysnail.net>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>

diff --git a/net/ipv4/esp4.c b/net/ipv4/esp4.c
index 10e809b..fb065a8 100644 (file)
--- a/net/ipv4/esp4.c
+++ b/net/ipv4/esp4.c
@@ -226,7 +226,7 @@ static void esp_output_fill_trailer(u8 *tail, int tfclen, int plen, __u8 proto)
        tail[plen - 1] = proto;
 }
 
-static void esp_output_udp_encap(struct xfrm_state *x, struct sk_buff *skb, struct esp_info *esp)
+static int esp_output_udp_encap(struct xfrm_state *x, struct sk_buff *skb, struct esp_info *esp)
 {
        int encap_type;
        struct udphdr *uh;
@@ -234,6 +234,7 @@ static void esp_output_udp_encap(struct xfrm_state *x, struct sk_buff *skb, stru
        __be16 sport, dport;
        struct xfrm_encap_tmpl *encap = x->encap;
        struct ip_esp_hdr *esph = esp->esph;
+       unsigned int len;
 
        spin_lock_bh(&x->lock);
        sport = encap->encap_sport;
@@ -241,11 +242,14 @@ static void esp_output_udp_encap(struct xfrm_state *x, struct sk_buff *skb, stru
        encap_type = encap->encap_type;
        spin_unlock_bh(&x->lock);
 
+       len = skb->len + esp->tailen - skb_transport_offset(skb);
+       if (len + sizeof(struct iphdr) >= IP_MAX_MTU)
+               return -EMSGSIZE;
+
        uh = (struct udphdr *)esph;
        uh->source = sport;
        uh->dest = dport;
-       uh->len = htons(skb->len + esp->tailen
-                 - skb_transport_offset(skb));
+       uh->len = htons(len);
        uh->check = 0;
 
        switch (encap_type) {
@@ -262,6 +266,8 @@ static void esp_output_udp_encap(struct xfrm_state *x, struct sk_buff *skb, stru
 
        *skb_mac_header(skb) = IPPROTO_UDP;
        esp->esph = esph;
+
+       return 0;
 }
 
 int esp_output_head(struct xfrm_state *x, struct sk_buff *skb, struct esp_info *esp)
@@ -275,8 +281,12 @@ int esp_output_head(struct xfrm_state *x, struct sk_buff *skb, struct esp_info *
        int tailen = esp->tailen;
 
        /* this is non-NULL only with UDP Encapsulation */
-       if (x->encap)
-               esp_output_udp_encap(x, skb, esp);
+       if (x->encap) {
+               int err = esp_output_udp_encap(x, skb, esp);
+
+               if (err < 0)
+                       return err;
+       }
 
        if (!skb_cloned(skb)) {
                if (tailen <= skb_tailroom(skb)) {