6lowpan: move skb_free from error paths in decompression

Currently we ensure that the skb is freed on every error path in IPHC
decompression which makes it easy to introduce skb leaks.  By centralising
the skb_free into the receive function it makes future decompression routines
easier to maintain.  It does come at the expense of ensuring that the skb
passed into the decompression routine must not be copied.

Signed-off-by: Martin Townsend <mtownsend1973@gmail.com>
Acked-by: Jukka Rissanen <jukka.rissanen@linux.intel.com>
Acked-by: Alexander Aring <alex.aring@gmail.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>

1 files changed, 12 insertions, 19 deletions

diff --git a/net/6lowpan/iphc.c b/net/6lowpan/iphc.c
index cd5f8b8e34cd..aced97db62f0 100644
--- a/net/6lowpan/iphc.c
+++ b/net/6lowpan/iphc.c
@@ -319,7 +319,7 @@ lowpan_header_decompress(struct sk_buff *skb, struct net_device *dev,
 	if (iphc1 & LOWPAN_IPHC_CID) {
 		pr_debug("CID flag is set, increase header with one\n");
 		if (lowpan_fetch_skb(skb, &num_context, sizeof(num_context)))
-			goto drop;
+			return -EINVAL;
 	}
 
 	hdr.version = 6;
@@ -331,7 +331,7 @@ lowpan_header_decompress(struct sk_buff *skb, struct net_device *dev,
 	 */
 	case 0: /* 00b */
 		if (lowpan_fetch_skb(skb, &tmp, sizeof(tmp)))
-			goto drop;
+			return -EINVAL;
 
 		memcpy(&hdr.flow_lbl, &skb->data[0], 3);
 		skb_pull(skb, 3);
@@ -344,7 +344,7 @@ lowpan_header_decompress(struct sk_buff *skb, struct net_device *dev,
 	 */
 	case 2: /* 10b */
 		if (lowpan_fetch_skb(skb, &tmp, sizeof(tmp)))
-			goto drop;
+			return -EINVAL;
 
 		hdr.priority = ((tmp >> 2) & 0x0f);
 		hdr.flow_lbl[0] = ((tmp << 6) & 0xC0) | ((tmp >> 2) & 0x30);
@@ -354,7 +354,7 @@ lowpan_header_decompress(struct sk_buff *skb, struct net_device *dev,
 	 */
 	case 1: /* 01b */
 		if (lowpan_fetch_skb(skb, &tmp, sizeof(tmp)))
-			goto drop;
+			return -EINVAL;
 
 		hdr.flow_lbl[0] = (skb->data[0] & 0x0F) | ((tmp >> 2) & 0x30);
 		memcpy(&hdr.flow_lbl[1], &skb->data[0], 2);
@@ -371,7 +371,7 @@ lowpan_header_decompress(struct sk_buff *skb, struct net_device *dev,
 	if ((iphc0 & LOWPAN_IPHC_NH_C) == 0) {
 		/* Next header is carried inline */
 		if (lowpan_fetch_skb(skb, &hdr.nexthdr, sizeof(hdr.nexthdr)))
-			goto drop;
+			return -EINVAL;
 
 		pr_debug("NH flag is set, next header carried inline: %02x\n",
 			 hdr.nexthdr);
@@ -383,7 +383,7 @@ lowpan_header_decompress(struct sk_buff *skb, struct net_device *dev,
 	} else {
 		if (lowpan_fetch_skb(skb, &hdr.hop_limit,
 				     sizeof(hdr.hop_limit)))
-			goto drop;
+			return -EINVAL;
 	}
 
 	/* Extract SAM to the tmp variable */
@@ -402,7 +402,7 @@ lowpan_header_decompress(struct sk_buff *skb, struct net_device *dev,
 
 	/* Check on error of previous branch */
 	if (err)
-		goto drop;
+		return -EINVAL;
 
 	/* Extract DAM to the tmp variable */
 	tmp = ((iphc1 & LOWPAN_IPHC_DAM_11) >> LOWPAN_IPHC_DAM_BIT) & 0x03;
@@ -417,7 +417,7 @@ lowpan_header_decompress(struct sk_buff *skb, struct net_device *dev,
 								tmp);
 
 			if (err)
-				goto drop;
+				return -EINVAL;
 		}
 	} else {
 		err = uncompress_addr(skb, &hdr.daddr, tmp, daddr,
@@ -425,7 +425,7 @@ lowpan_header_decompress(struct sk_buff *skb, struct net_device *dev,
 		pr_debug("dest: stateless compression mode %d dest %pI6c\n",
 			 tmp, &hdr.daddr);
 		if (err)
-			goto drop;
+			return -EINVAL;
 	}
 
 	/* UDP data uncompression */
@@ -434,16 +434,14 @@ lowpan_header_decompress(struct sk_buff *skb, struct net_device *dev,
 		const int needed = sizeof(struct udphdr) + sizeof(hdr);
 
 		if (uncompress_udp_header(skb, &uh))
-			goto drop;
+			return -EINVAL;
 
 		/* replace the compressed UDP head by the uncompressed UDP
 		 * header
 		 */
 		err = skb_cow(skb, needed);
-		if (unlikely(err)) {
-			kfree_skb(skb);
+		if (unlikely(err))
 			return err;
-		}
 
 		skb_push(skb, sizeof(struct udphdr));
 		skb_reset_transport_header(skb);
@@ -455,10 +453,8 @@ lowpan_header_decompress(struct sk_buff *skb, struct net_device *dev,
 		hdr.nexthdr = UIP_PROTO_UDP;
 	} else {
 		err = skb_cow(skb, sizeof(hdr));
-		if (unlikely(err)) {
-			kfree_skb(skb);
+		if (unlikely(err))
 			return err;
-		}
 	}
 
 	hdr.payload_len = htons(skb->len);
@@ -478,9 +474,6 @@ lowpan_header_decompress(struct sk_buff *skb, struct net_device *dev,
 	raw_dump_table(__func__, "raw header dump", (u8 *)&hdr, sizeof(hdr));
 
 	return 0;
-drop:
-	kfree_skb(skb);
-	return -EINVAL;
 }
 EXPORT_SYMBOL_GPL(lowpan_header_decompress);