[SCTP]: Fix sctp_cookie alignment in the packet.

On 64 bit architectures, sctp_cookie sent as part of INIT-ACK is not
aligned on a 64 bit boundry and thus causes unaligned access exceptions.

The layout of the cookie prameter is this:
|<----- Parameter Header --------------------|<--- Cookie DATA --------
-----------------------------------------------------------------------
| param type (16 bits) | param len (16 bits) | sig [32 bytes] | cookie..
-----------------------------------------------------------------------

The cookie data portion contains 64 bit values on 64 bit architechtures
(timeval) that fall on a 32 bit alignment boundry when used as part of
the on-wire format, but align correctly when used in internal
structures.  This patch explicitely pads the on-wire format so that
it is properly aligned.

Signed-off-by: Vlad Yasevich <vladislav.yasevich@hp.com>
Signed-off-by: Sridhar Samudrala <sri@us.ibm.com>

include/net/sctp/structs.h

@@ -405,8 +405,9 @@ struct sctp_cookie {
 /* The format of our cookie that we send to our peer. */
 struct sctp_signed_cookie {
 	__u8 signature[SCTP_SECRET_SIZE];
+	__u32 __pad;		/* force sctp_cookie alignment to 64 bits */
 	struct sctp_cookie c;
-};
+} __attribute__((packed));
 
 /* This is another convenience type to allocate memory for address
  * params for the maximum size and pass such structures around

net/sctp/sm_make_chunk.c

@@ -1275,7 +1275,12 @@ static sctp_cookie_param_t *sctp_pack_cookie(const struct sctp_endpoint *ep,
 	unsigned int keylen;
 	char *key;
 
-	headersize = sizeof(sctp_paramhdr_t) + SCTP_SECRET_SIZE;
+	/* Header size is static data prior to the actual cookie, including
+	 * any padding.
+	 */
+	headersize = sizeof(sctp_paramhdr_t) + 
+		     (sizeof(struct sctp_signed_cookie) - 
+		      sizeof(struct sctp_cookie));
 	bodysize = sizeof(struct sctp_cookie)
 		+ ntohs(init_chunk->chunk_hdr->length) + addrs_len;
 
@@ -1362,7 +1367,12 @@ struct sctp_association *sctp_unpack_cookie(
 	struct sk_buff *skb = chunk->skb;
 	struct timeval tv;
 
-	headersize = sizeof(sctp_chunkhdr_t) + SCTP_SECRET_SIZE;
+	/* Header size is static data prior to the actual cookie, including
+	 * any padding.
+	 */
+	headersize = sizeof(sctp_chunkhdr_t) +
+		     (sizeof(struct sctp_signed_cookie) - 
+		      sizeof(struct sctp_cookie));
 	bodysize = ntohs(chunk->chunk_hdr->length) - headersize;
 	fixed_size = headersize + sizeof(struct sctp_cookie);