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net: defragment IP packets

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The defragmenting code is enabled by CONFIG_IP_DEFRAG; the code is
useful for TFTP and NFS transfers.  The user can specify the maximum
defragmented payload as CONFIG_NET_MAXDEFRAG (default 16k).
Since NFS has a bigger per-packet overhead than TFTP, the static
reassembly buffer can hold CONFIG_NET_MAXDEFRAG + the NFS overhead.

The packet buffer is used as an array of "hole" structures, acting as
a double-linked list. Each new fragment can split a hole in two,
reduce a hole or fill a hole. No support is there for a fragment
overlapping two diffrent holes (i.e., thre new fragment is across an
already-received fragment).

Signed-off-by: Alessandro Rubini <rubini@gnudd.com>
Signed-off-by: Ben Warren <biggerbadderben@gmail.com>
master
Alessandro Rubini 16 years ago committed by Ben Warren
parent 307ecb6db0
commit 5cfaa4e54d
1 changed files with 183 additions and 5 deletions
  1. 188
      net/net.c

188
net/net.c
Unescape View File

@ -1107,6 +1107,176 @@ static void CDPStart(void)
}
#endif
#ifdef CONFIG_IP_DEFRAG
/*
* This function collects fragments in a single packet, according
* to the algorithm in RFC815. It returns NULL or the pointer to
* a complete packet, in static storage
*/
#ifndef CONFIG_NET_MAXDEFRAG
#define CONFIG_NET_MAXDEFRAG 16384
#endif
/*
* MAXDEFRAG, above, is chosen in the config file and is real data
* so we need to add the NFS overhead, which is more than TFTP.
* To use sizeof in the internal unnamed structures, we need a real
* instance (can't do "sizeof(struct rpc_t.u.reply))", unfortunately).
* The compiler doesn't complain nor allocates the actual structure
*/
static struct rpc_t rpc_specimen;
#define IP_PKTSIZE (CONFIG_NET_MAXDEFRAG + sizeof(rpc_specimen.u.reply))
#define IP_MAXUDP (IP_PKTSIZE - IP_HDR_SIZE_NO_UDP)
/*
* this is the packet being assembled, either data or frag control.
* Fragments go by 8 bytes, so this union must be 8 bytes long
*/
struct hole {
/* first_byte is address of this structure */
u16 last_byte; /* last byte in this hole + 1 (begin of next hole) */
u16 next_hole; /* index of next (in 8-b blocks), 0 == none */
u16 prev_hole; /* index of prev, 0 == none */
u16 unused;
};
static IP_t *__NetDefragment(IP_t *ip, int *lenp)
{
static uchar pkt_buff[IP_PKTSIZE] __attribute__((aligned(PKTALIGN)));
static u16 first_hole, total_len;
struct hole *payload, *thisfrag, *h, *newh;
IP_t *localip = (IP_t *)pkt_buff;
uchar *indata = (uchar *)ip;
int offset8, start, len, done = 0;
u16 ip_off = ntohs(ip->ip_off);
/* payload starts after IP header, this fragment is in there */
payload = (struct hole *)(pkt_buff + IP_HDR_SIZE_NO_UDP);
offset8 = (ip_off & IP_OFFS);
thisfrag = payload + offset8;
start = offset8 * 8;
len = ntohs(ip->ip_len) - IP_HDR_SIZE_NO_UDP;
if (start + len > IP_MAXUDP) /* fragment extends too far */
return NULL;
if (!total_len || localip->ip_id != ip->ip_id) {
/* new (or different) packet, reset structs */
total_len = 0xffff;
payload[0].last_byte = ~0;
payload[0].next_hole = 0;
payload[0].prev_hole = 0;
first_hole = 0;
/* any IP header will work, copy the first we received */
memcpy(localip, ip, IP_HDR_SIZE_NO_UDP);
}
/*
* What follows is the reassembly algorithm. We use the payload
* array as a linked list of hole descriptors, as each hole starts
* at a multiple of 8 bytes. However, last byte can be whatever value,
* so it is represented as byte count, not as 8-byte blocks.
*/
h = payload + first_hole;
while (h->last_byte < start) {
if (!h->next_hole) {
/* no hole that far away */
return NULL;
}
h = payload + h->next_hole;
}
if (offset8 + (len / 8) <= h - payload) {
/* no overlap with holes (dup fragment?) */
return NULL;
}
if (!(ip_off & IP_FLAGS_MFRAG)) {
/* no more fragmentss: truncate this (last) hole */
total_len = start + len;
h->last_byte = start + len;
}
/*
* There is some overlap: fix the hole list. This code doesn't
* deal with a fragment that overlaps with two different holes
* (thus being a superset of a previously-received fragment).
*/
if ( (h >= thisfrag) && (h->last_byte <= start + len) ) {
/* complete overlap with hole: remove hole */
if (!h->prev_hole && !h->next_hole) {
/* last remaining hole */
done = 1;
} else if (!h->prev_hole) {
/* first hole */
first_hole = h->next_hole;
payload[h->next_hole].prev_hole = 0;
} else if (!h->next_hole) {
/* last hole */
payload[h->prev_hole].next_hole = 0;
} else {
/* in the middle of the list */
payload[h->next_hole].prev_hole = h->prev_hole;
payload[h->prev_hole].next_hole = h->next_hole;
}
} else if (h->last_byte <= start + len) {
/* overlaps with final part of the hole: shorten this hole */
h->last_byte = start;
} else if (h >= thisfrag) {
/* overlaps with initial part of the hole: move this hole */
newh = thisfrag + (len / 8);
*newh = *h;
h = newh;
if (h->next_hole)
payload[h->next_hole].prev_hole = (h - payload);
if (h->prev_hole)
payload[h->prev_hole].next_hole = (h - payload);
else
first_hole = (h - payload);
} else {
/* fragment sits in the middle: split the hole */
newh = thisfrag + (len / 8);
*newh = *h;
h->last_byte = start;
h->next_hole = (newh - payload);
newh->prev_hole = (h - payload);
if (newh->next_hole)
payload[newh->next_hole].prev_hole = (newh - payload);
}
/* finally copy this fragment and possibly return whole packet */
memcpy((uchar *)thisfrag, indata + IP_HDR_SIZE_NO_UDP, len);
if (!done)
return NULL;
localip->ip_len = htons(total_len);
*lenp = total_len + IP_HDR_SIZE_NO_UDP;
return localip;
}
static inline IP_t *NetDefragment(IP_t *ip, int *lenp)
{
u16 ip_off = ntohs(ip->ip_off);
if (!(ip_off & (IP_OFFS | IP_FLAGS_MFRAG)))
return ip; /* not a fragment */
return __NetDefragment(ip, lenp);
}
#else /* !CONFIG_IP_DEFRAG */
static inline IP_t *NetDefragment(IP_t *ip, int *lenp)
{
u16 ip_off = ntohs(ip->ip_off);
if (!(ip_off & (IP_OFFS | IP_FLAGS_MFRAG)))
return ip; /* not a fragment */
return NULL;
}
#endif
void
NetReceive(volatile uchar * inpkt, int len)
@ -1333,10 +1503,12 @@ NetReceive(volatile uchar * inpkt, int len)
case PROT_IP:
debug("Got IP\n");
/* Before we start poking the header, make sure it is there */
if (len < IP_HDR_SIZE) {
debug("len bad %d < %lu\n", len, (ulong)IP_HDR_SIZE);
return;
}
/* Check the packet length */
if (len < ntohs(ip->ip_len)) {
printf("len bad %d < %d\n", len, ntohs(ip->ip_len));
return;
@ -1344,21 +1516,20 @@ NetReceive(volatile uchar * inpkt, int len)
len = ntohs(ip->ip_len);
debug("len=%d, v=%02x\n", len, ip->ip_hl_v & 0xff);
/* Can't deal with anything except IPv4 */
if ((ip->ip_hl_v & 0xf0) != 0x40) {
return;
}
/* Can't deal with fragments */
if (ip->ip_off & htons(IP_OFFS | IP_FLAGS_MFRAG)) {
return;
}
/* can't deal with headers > 20 bytes */
/* Can't deal with IP options (headers != 20 bytes) */
if ((ip->ip_hl_v & 0x0f) > 0x05) {
return;
}
/* Check the Checksum of the header */
if (!NetCksumOk((uchar *)ip, IP_HDR_SIZE_NO_UDP / 2)) {
puts ("checksum bad\n");
return;
}
/* If it is not for us, ignore it */
tmp = NetReadIP(&ip->ip_dst);
if (NetOurIP && tmp != NetOurIP && tmp != 0xFFFFFFFF) {
#ifdef CONFIG_MCAST_TFTP
@ -1367,6 +1538,13 @@ NetReceive(volatile uchar * inpkt, int len)
return;
}
/*
* The function returns the unchanged packet if it's not
* a fragment, and either the complete packet or NULL if
* it is a fragment (if !CONFIG_IP_DEFRAG, it returns NULL)
*/
if (!(ip = NetDefragment(ip, &len)))
return;
/*
* watch for ICMP host redirects
*
* There is no real handler code (yet). We just watch

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