ieee802154: add definitions for link-layer security and header functions

When dealing with 802.15.4, one often has to know the maximum payload
size for a given packet. This depends on many factors, one of which is
whether or not a security header is present in the frame. These
definitions and functions provide an easy way for any upper layer to
calculate the maximum payload size for a packet. The first obvious user
for this is 6lowpan, which duplicates this calculation and gets it
partially wrong because it ignores security headers.

Signed-off-by: Phoebe Buckheister <phoebe.buckheister@itwm.fraunhofer.de>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 45 insertions, 7 deletions

diff --git a/net/ieee802154/header_ops.c b/net/ieee802154/header_ops.c
index bed42a48408c..c09294e39ca6 100644
--- a/net/ieee802154/header_ops.c
+++ b/net/ieee802154/header_ops.c
@@ -195,15 +195,16 @@ ieee802154_hdr_get_sechdr(const u8 *buf, struct ieee802154_sechdr *hdr)
         return pos;
 }
 
+static int ieee802154_sechdr_lengths[4] = {
+        [IEEE802154_SCF_KEY_IMPLICIT] = 5,
+        [IEEE802154_SCF_KEY_INDEX] = 6,
+        [IEEE802154_SCF_KEY_SHORT_INDEX] = 10,
+        [IEEE802154_SCF_KEY_HW_INDEX] = 14,
+};
+
 static int ieee802154_hdr_sechdr_len(u8 sc)
 {
-        switch (IEEE802154_SCF_KEY_ID_MODE(sc)) {
-        case IEEE802154_SCF_KEY_IMPLICIT: return 5;
-        case IEEE802154_SCF_KEY_INDEX: return 6;
-        case IEEE802154_SCF_KEY_SHORT_INDEX: return 10;
-        case IEEE802154_SCF_KEY_HW_INDEX: return 14;
-        default: return -EINVAL;
-        }
+        return ieee802154_sechdr_lengths[IEEE802154_SCF_KEY_ID_MODE(sc)];
 }
 
 static int ieee802154_hdr_minlen(const struct ieee802154_hdr *hdr)
@@ -285,3 +286,40 @@ ieee802154_hdr_peek_addrs(const struct sk_buff *skb, struct ieee802154_hdr *hdr)
         return pos;
 }
 EXPORT_SYMBOL_GPL(ieee802154_hdr_peek_addrs);
+
+int
+ieee802154_hdr_peek(const struct sk_buff *skb, struct ieee802154_hdr *hdr)
+{
+        const u8 *buf = skb_mac_header(skb);
+        int pos;
+
+        pos = ieee802154_hdr_peek_addrs(skb, hdr);
+        if (pos < 0)
+                return -EINVAL;
+
+        if (hdr->fc.security_enabled) {
+                u8 key_id_mode = IEEE802154_SCF_KEY_ID_MODE(*(buf + pos));
+                int want = pos + ieee802154_sechdr_lengths[key_id_mode];
+
+                if (buf + want > skb_tail_pointer(skb))
+                        return -EINVAL;
+
+                pos += ieee802154_hdr_get_sechdr(buf + pos, &hdr->sec);
+        }
+
+        return pos;
+}
+EXPORT_SYMBOL_GPL(ieee802154_hdr_peek);
+
+int ieee802154_max_payload(const struct ieee802154_hdr *hdr)
+{
+        int hlen = ieee802154_hdr_minlen(hdr);
+
+        if (hdr->fc.security_enabled) {
+                hlen += ieee802154_sechdr_lengths[hdr->sec.key_id_mode] - 1;
+                hlen += ieee802154_sechdr_authtag_len(&hdr->sec);
+        }
+
+        return IEEE802154_MTU - hlen - IEEE802154_MFR_SIZE;
+}
+EXPORT_SYMBOL_GPL(ieee802154_max_payload);