net: Export IGMP/MLD message validation code

With this patch, the IGMP and MLD message validation functions are moved
from the bridge code to IPv4/IPv6 multicast files. Some small
refactoring was done to enhance readibility and to iron out some
differences in behaviour between the IGMP and MLD parsing code (e.g. the
skb-cloning of MLD messages is now only done if necessary, just like the
IGMP part always did).

Finally, these IGMP and MLD message validation functions are exported so
that not only the bridge can use it but batman-adv later, too.

Signed-off-by: Linus Lüssing <linus.luessing@c0d3.blue>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 87 insertions, 0 deletions

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 3cfff2a3d651..1e4278a4dd7e 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -4030,6 +4030,93 @@ int skb_checksum_setup(struct sk_buff *skb, bool recalculate)
 }
 EXPORT_SYMBOL(skb_checksum_setup);
 
+/**
+ * skb_checksum_maybe_trim - maybe trims the given skb
+ * @skb: the skb to check
+ * @transport_len: the data length beyond the network header
+ *
+ * Checks whether the given skb has data beyond the given transport length.
+ * If so, returns a cloned skb trimmed to this transport length.
+ * Otherwise returns the provided skb. Returns NULL in error cases
+ * (e.g. transport_len exceeds skb length or out-of-memory).
+ *
+ * Caller needs to set the skb transport header and release the returned skb.
+ * Provided skb is consumed.
+ */
+static struct sk_buff *skb_checksum_maybe_trim(struct sk_buff *skb,
+                                               unsigned int transport_len)
+{
+        struct sk_buff *skb_chk;
+        unsigned int len = skb_transport_offset(skb) + transport_len;
+        int ret;
+
+        if (skb->len < len) {
+                kfree_skb(skb);
+                return NULL;
+        } else if (skb->len == len) {
+                return skb;
+        }
+
+        skb_chk = skb_clone(skb, GFP_ATOMIC);
+        kfree_skb(skb);
+
+        if (!skb_chk)
+                return NULL;
+
+        ret = pskb_trim_rcsum(skb_chk, len);
+        if (ret) {
+                kfree_skb(skb_chk);
+                return NULL;
+        }
+
+        return skb_chk;
+}
+
+/**
+ * skb_checksum_trimmed - validate checksum of an skb
+ * @skb: the skb to check
+ * @transport_len: the data length beyond the network header
+ * @skb_chkf: checksum function to use
+ *
+ * Applies the given checksum function skb_chkf to the provided skb.
+ * Returns a checked and maybe trimmed skb. Returns NULL on error.
+ *
+ * If the skb has data beyond the given transport length, then a
+ * trimmed & cloned skb is checked and returned.
+ *
+ * Caller needs to set the skb transport header and release the returned skb.
+ * Provided skb is consumed.
+ */
+struct sk_buff *skb_checksum_trimmed(struct sk_buff *skb,
+                                     unsigned int transport_len,
+                                     __sum16(*skb_chkf)(struct sk_buff *skb))
+{
+        struct sk_buff *skb_chk;
+        unsigned int offset = skb_transport_offset(skb);
+        int ret;
+
+        skb_chk = skb_checksum_maybe_trim(skb, transport_len);
+        if (!skb_chk)
+                return NULL;
+
+        if (!pskb_may_pull(skb_chk, offset)) {
+                kfree_skb(skb_chk);
+                return NULL;
+        }
+
+        __skb_pull(skb_chk, offset);
+        ret = skb_chkf(skb_chk);
+        __skb_push(skb_chk, offset);
+
+        if (ret) {
+                kfree_skb(skb_chk);
+                return NULL;
+        }
+
+        return skb_chk;
+}
+EXPORT_SYMBOL(skb_checksum_trimmed);
+
 void __skb_warn_lro_forwarding(const struct sk_buff *skb)
 {
         net_warn_ratelimited("%s: received packets cannot be forwarded while LRO is enabled\n",