bridge: simplify ip_mc_check_igmp() and ipv6_mc_check_mld() calls

This patch refactors ip_mc_check_igmp(), ipv6_mc_check_mld() and
their callers (more precisely, the Linux bridge) to not rely on
the skb_trimmed parameter anymore.

An skb with its tail trimmed to the IP packet length was initially
introduced for the following three reasons:

1) To be able to verify the ICMPv6 checksum.
2) To be able to distinguish the version of an IGMP or MLD query.
   They are distinguishable only by their size.
3) To avoid parsing data for an IGMPv3 or MLDv2 report that is
   beyond the IP packet but still within the skb.

The first case still uses a cloned and potentially trimmed skb to
verfiy. However, there is no need to propagate it to the caller.
For the second and third case explicit IP packet length checks were
added.

This hopefully makes ip_mc_check_igmp() and ipv6_mc_check_mld() easier
to read and verfiy, as well as easier to use.

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

1 files changed, 4 insertions, 19 deletions

diff --git a/net/ipv4/igmp.c b/net/ipv4/igmp.c
index 765b2b32c4a4..b1f6d93282d7 100644
--- a/net/ipv4/igmp.c
+++ b/net/ipv4/igmp.c
@@ -1544,7 +1544,7 @@ static inline __sum16 ip_mc_validate_checksum(struct sk_buff *skb)
 	return skb_checksum_simple_validate(skb);
 }
 
-static int __ip_mc_check_igmp(struct sk_buff *skb, struct sk_buff **skb_trimmed)
+static int __ip_mc_check_igmp(struct sk_buff *skb)
 
 {
 	struct sk_buff *skb_chk;
@@ -1566,16 +1566,10 @@ static int __ip_mc_check_igmp(struct sk_buff *skb, struct sk_buff **skb_trimmed)
 	if (ret)
 		goto err;
 
-	if (skb_trimmed)
-		*skb_trimmed = skb_chk;
-	/* free now unneeded clone */
-	else if (skb_chk != skb)
-		kfree_skb(skb_chk);
-
 	ret = 0;
 
 err:
-	if (ret && skb_chk && skb_chk != skb)
+	if (skb_chk && skb_chk != skb)
 		kfree_skb(skb_chk);
 
 	return ret;
@@ -1584,7 +1578,6 @@ err:
 /**
  * ip_mc_check_igmp - checks whether this is a sane IGMP packet
  * @skb: the skb to validate
- * @skb_trimmed: to store an skb pointer trimmed to IPv4 packet tail (optional)
  *
  * Checks whether an IPv4 packet is a valid IGMP packet. If so sets
  * skb transport header accordingly and returns zero.
@@ -1594,18 +1587,10 @@ err:
  * -ENOMSG: IP header validation succeeded but it is not an IGMP packet.
  * -ENOMEM: A memory allocation failure happened.
  *
- * Optionally, an skb pointer might be provided via skb_trimmed (or set it
- * to NULL): After parsing an IGMP packet successfully it will point to
- * an skb which has its tail aligned to the IP packet end. This might
- * either be the originally provided skb or a trimmed, cloned version if
- * the skb frame had data beyond the IP packet. A cloned skb allows us
- * to leave the original skb and its full frame unchanged (which might be
- * desirable for layer 2 frame jugglers).
- *
  * Caller needs to set the skb network header and free any returned skb if it
  * differs from the provided skb.
  */
-int ip_mc_check_igmp(struct sk_buff *skb, struct sk_buff **skb_trimmed)
+int ip_mc_check_igmp(struct sk_buff *skb)
 {
 	int ret = ip_mc_check_iphdr(skb);
 
@@ -1615,7 +1600,7 @@ int ip_mc_check_igmp(struct sk_buff *skb, struct sk_buff **skb_trimmed)
 	if (ip_hdr(skb)->protocol != IPPROTO_IGMP)
 		return -ENOMSG;
 
-	return __ip_mc_check_igmp(skb, skb_trimmed);
+	return __ip_mc_check_igmp(skb);
 }
 EXPORT_SYMBOL(ip_mc_check_igmp);