Commit 77edab64 authored by Ondřej Zajíček's avatar Ondřej Zajíček

OSPF: Redesign LSA checksumming

New LSA checksumming code separates generic Fletcher-16 and OSPF-specific
code and avoids back and forth endianity conversions, making it much more
readable and also several times faster.
parent 30d09eb9
/*
* BIRD Library -- Fletcher-16 checksum
*
* (c) 2015 Ondrej Zajicek <santiago@crfreenet.org>
* (c) 2015 CZ.NIC z.s.p.o.
*
* Can be freely distributed and used under the terms of the GNU GPL.
*/
/**
* DOC: Fletcher-16 checksum
*
* Fletcher-16 checksum is a position-dependent checksum algorithm used for
* error-detection e.g. in OSPF LSAs.
*
* To generate Fletcher-16 checksum, zero the checksum field in data, initialize
* the context by fletcher16_init(), process the data by fletcher16_update(),
* compute the checksum value by fletcher16_final() and store it to the checksum
* field in data by put_u16() (or other means involving htons() conversion).
*
* To verify Fletcher-16 checksum, initialize the context by fletcher16_init(),
* process the data by fletcher16_update(), compute a passing checksum by
* fletcher16_compute() and check if it is zero.
*/
#ifndef _BIRD_FLETCHER16_H_
#define _BIRD_FLETCHER16_H_
#include "nest/bird.h"
struct fletcher16_context
{
int c0, c1;
};
/**
* fletcher16_init - initialize Fletcher-16 context
* @ctx: the context
*/
static inline void
fletcher16_init(struct fletcher16_context *ctx)
{
ctx->c0 = ctx->c1 = 0;
}
/**
* fletcher16_update - process data to Fletcher-16 context
* @ctx: the context
* @buf: data buffer
* @len: data length
*
* fletcher16_update() reads data from the buffer @buf and updates passing sums
* in the context @ctx. It may be used multiple times for multiple blocks of
* checksummed data.
*/
static inline void
fletcher16_update(struct fletcher16_context *ctx, const u8* buf, int len)
{
/*
* The Fletcher-16 sum is essentially a sequence of
* ctx->c1 += ctx->c0 += *buf++, modulo 255.
*
* In the inner loop, we eliminate modulo operation and we do some loop
* unrolling. MODX is the maximal number of steps that can be done without
* modulo before overflow, see RFC 1008 for details. We use a bit smaller
* value to cover for initial steps due to loop unrolling.
*/
#define MODX 4096
int blen, i;
blen = len % 4;
len -= blen;
for (i = 0; i < blen; i++)
ctx->c1 += ctx->c0 += *buf++;
do {
blen = MIN(len, MODX);
len -= blen;
for (i = 0; i < blen; i += 4)
{
ctx->c1 += ctx->c0 += *buf++;
ctx->c1 += ctx->c0 += *buf++;
ctx->c1 += ctx->c0 += *buf++;
ctx->c1 += ctx->c0 += *buf++;
}
ctx->c0 %= 255;
ctx->c1 %= 255;
} while (len);
}
/**
* fletcher16_update_n32 - process data to Fletcher-16 context, with endianity adjustment
* @ctx: the context
* @buf: data buffer
* @len: data length
*
* fletcher16_update_n32() works like fletcher16_update(), except it applies
* 32-bit host/network endianity swap to the data before they are processed.
* I.e., it assumes that the data is a sequence of u32 that must be converted by
* ntohl() or htonl() before processing. The @buf need not to be aligned, but
* its length (@len) must be multiple of 4. Note that on big endian systems the
* host endianity is the same as the network endianity, therefore there is no
* endianity swap.
*/
static inline void
fletcher16_update_n32(struct fletcher16_context *ctx, const u8* buf, int len)
{
/* See fletcher16_update() for details */
int blen, i;
do {
blen = MIN(len, MODX);
len -= blen;
for (i = 0; i < blen; i += 4)
{
#ifdef CPU_BIG_ENDIAN
ctx->c1 += ctx->c0 += *buf++;
ctx->c1 += ctx->c0 += *buf++;
ctx->c1 += ctx->c0 += *buf++;
ctx->c1 += ctx->c0 += *buf++;
#else
ctx->c1 += ctx->c0 += buf[3];
ctx->c1 += ctx->c0 += buf[2];
ctx->c1 += ctx->c0 += buf[1];
ctx->c1 += ctx->c0 += buf[0];
buf += 4;
#endif
}
ctx->c0 %= 255;
ctx->c1 %= 255;
} while (len);
}
/**
* fletcher16_final - compute final Fletcher-16 checksum value
* @ctx: the context
* @len: total data length
* @pos: offset in data where the checksum will be stored
*
* fletcher16_final() computes the final checksum value and returns it.
* The caller is responsible for storing it in the appropriate position.
* The checksum value depends on @len and @pos, but only their difference
* (i.e. the offset from the end) is significant.
*
* The checksum value is represented as u16, although it is defined as two
* consecutive bytes. We treat them as one u16 in big endian / network order.
* I.e., the returned value is in the form that would be returned by get_u16()
* from the checksum field in the data buffer, therefore the caller should use
* put_u16() or an explicit host-to-network conversion when storing it to the
* checksum field in the data buffer.
*
* Note that the returned checksum value is always nonzero.
*/
static inline u16
fletcher16_final(struct fletcher16_context *ctx, int len, int pos)
{
int x = ((len - pos - 1) * ctx->c0 - ctx->c1) % 255;
if (x <= 0)
x += 255;
int y = 510 - ctx->c0 - x;
if (y > 255)
y -= 255;
return (x << 8) | y;
}
/**
* fletcher16_compute - compute Fletcher-16 sum for verification
* @ctx: the context
*
* fletcher16_compute() returns a passing Fletcher-16 sum for processed data.
* If the data contains the proper Fletcher-16 checksum value, the returned
* value is zero.
*/
static inline u16
fletcher16_compute(struct fletcher16_context *ctx)
{
return (ctx->c0 << 8) | ctx->c1;
}
#endif
......@@ -2,14 +2,15 @@
* BIRD -- OSPF
*
* (c) 1999--2004 Ondrej Filip <feela@network.cz>
* (c) 2009--2014 Ondrej Zajicek <santiago@crfreenet.org>
* (c) 2009--2014 CZ.NIC z.s.p.o.
* (c) 2009--2015 Ondrej Zajicek <santiago@crfreenet.org>
* (c) 2009--2015 CZ.NIC z.s.p.o.
*
* Can be freely distributed and used under the terms of the GNU GPL.
*/
#include "ospf.h"
#include "lib/fletcher16.h"
#ifndef CPU_BIG_ENDIAN
void
......@@ -150,145 +151,41 @@ lsa_get_type_domain_(u32 itype, struct ospf_iface *ifa, u32 *otype, u32 *domain)
}
/*
void
buf_dump(const char *hdr, const byte *buf, int blen)
lsa_generate_checksum(struct ospf_lsa_header *lsa, const u8 *body)
{
char b2[1024];
char *bp;
int first = 1;
int i;
const char *lhdr = hdr;
bp = b2;
for(i = 0; i < blen; i++)
{
if ((i > 0) && ((i % 16) == 0))
{
*bp = 0;
log(L_WARN "%s\t%s", lhdr, b2);
lhdr = "";
bp = b2;
}
bp += snprintf(bp, 1022, "%02x ", buf[i]);
}
*bp = 0;
log(L_WARN "%s\t%s", lhdr, b2);
}
*/
#define MODX 4102 /* larges signed value without overflow */
/* Fletcher Checksum -- Refer to RFC1008. */
#define MODX 4102
#define LSA_CHECKSUM_OFFSET 15
/* FIXME This is VERY uneficient, I have huge endianity problems */
void
lsasum_calculate(struct ospf_lsa_header *h, void *body)
{
u16 length = h->length;
// log(L_WARN "Checksum %R %R %d start (len %d)", h->id, h->rt, h->type, length);
lsa_hton_hdr(h, h);
lsa_hton_body1(body, length - sizeof(struct ospf_lsa_header));
struct fletcher16_context ctx;
struct ospf_lsa_header hdr;
u16 len = lsa->length;
/*
char buf[1024];
memcpy(buf, h, sizeof(struct ospf_lsa_header));
memcpy(buf + sizeof(struct ospf_lsa_header), body, length - sizeof(struct ospf_lsa_header));
buf_dump("CALC", buf, length);
*/
* lsa and body are in the host order, we need to compute Fletcher-16 checksum
* for data in the network order. We also skip the initial age field.
*/
(void) lsasum_check(h, body, 1);
lsa_hton_hdr(lsa, &hdr);
hdr.checksum = 0;
// log(L_WARN "Checksum result %4x", h->checksum);
lsa_ntoh_hdr(h, h);
lsa_ntoh_body1(body, length - sizeof(struct ospf_lsa_header));
fletcher16_init(&ctx);
fletcher16_update(&ctx, (u8 *) &hdr + 2, sizeof(struct ospf_lsa_header) - 2);
fletcher16_update_n32(&ctx, body, len - sizeof(struct ospf_lsa_header));
lsa->checksum = fletcher16_final(&ctx, len, OFFSETOF(struct ospf_lsa_header, checksum));
}
/*
* Calculates the Fletcher checksum of an OSPF LSA.
*
* If 'update' is non-zero, the checkbytes (X and Y in RFC905) are calculated
* and the checksum field in the header is updated. The return value is the
* checksum as placed in the header (in network byte order).
*
* If 'update' is zero, only C0 and C1 are calculated and the header is kept
* intact. The return value is a combination of C0 and C1; if the return value
* is exactly zero the checksum is considered valid, any non-zero value is
* invalid.
*
* Note that this function expects the input LSA to be in network byte order.
*/
u16
lsasum_check(struct ospf_lsa_header *h, void *body, int update)
lsa_verify_checksum(const void *lsa_n, int lsa_len)
{
u8 *sp, *ep, *p, *q, *b;
int c0 = 0, c1 = 0;
int x, y;
u16 length;
b = body;
sp = (char *) h;
sp += 2; /* Skip Age field */
length = ntohs(h->length) - 2;
if (update) h->checksum = 0;
for (ep = sp + length; sp < ep; sp = q)
{ /* Actually MODX is very large, do we need the for-cyclus? */
q = sp + MODX;
if (q > ep)
q = ep;
for (p = sp; p < q; p++)
{
/*
* I count with bytes from header and than from body
* but if there is no body, it's appended to header
* (probably checksum in update receiving) and I go on
* after header
*/
if ((b == NULL) || (p < (u8 *) (h + 1)))
{
c0 += *p;
}
else
{
c0 += *(b + (p - (u8 *) (h + 1)));
}
c1 += c0;
}
c0 %= 255;
c1 %= 255;
}
struct fletcher16_context ctx;
if (!update) {
/*
* When testing the checksum, we don't need to calculate x and y. The
* checksum passes if c0 and c1 are both 0.
*/
return (c0 << 8) | (c1 & 0xff);
}
/* The whole LSA is at lsa_n in net order, we just skip initial age field */
x = (int)((length - LSA_CHECKSUM_OFFSET) * c0 - c1) % 255;
if (x <= 0)
x += 255;
y = 510 - c0 - x;
if (y > 255)
y -= 255;
fletcher16_init(&ctx);
fletcher16_update(&ctx, (u8 *) lsa_n + 2, lsa_len - 2);
((u8 *) & h->checksum)[0] = x;
((u8 *) & h->checksum)[1] = y;
return h->checksum;
return fletcher16_compute(&ctx) == 0;
}
int
lsa_comp(struct ospf_lsa_header *l1, struct ospf_lsa_header *l2)
/* Return codes from point of view of l1 */
......
......@@ -46,9 +46,9 @@ static inline u32 lsa_get_etype(struct ospf_lsa_header *h, struct ospf_proto *p)
int lsa_flooding_allowed(u32 type, u32 domain, struct ospf_iface *ifa);
void lsa_generate_checksum(struct ospf_lsa_header *lsa, const u8 *body);
u16 lsa_verify_checksum(const void *lsa_n, int lsa_len);
void lsasum_calculate(struct ospf_lsa_header *header, void *body);
u16 lsasum_check(struct ospf_lsa_header *h, void *body, int update);
#define CMP_NEWER 1
#define CMP_SAME 0
#define CMP_OLDER -1
......
......@@ -530,8 +530,8 @@ ospf_receive_lsupd(struct ospf_packet *pkt, struct ospf_iface *ifa,
DBG("Update Type: %04x, Id: %R, Rt: %R, Sn: 0x%08x, Age: %u, Sum: %u\n",
lsa_type, lsa.id, lsa.rt, lsa.sn, lsa.age, lsa.checksum);
/* RFC 2328 13. (1) - validate LSA checksum */
if ((lsa_n->checksum == 0) || (lsasum_check(lsa_n, NULL, 0) != 0))
/* RFC 2328 13. (1) - verify LSA checksum */
if ((lsa_n->checksum == 0) || !lsa_verify_checksum(lsa_n, lsa_len))
SKIP("invalid checksum");
/* RFC 2328 13. (2) */
......
......@@ -129,7 +129,7 @@ ospf_advance_lsa(struct ospf_proto *p, struct top_hash_entry *en, struct ospf_ls
en->lsa.age = 0;
en->init_age = 0;
en->inst_time = now;
lsasum_calculate(&en->lsa, en->lsa_body);
lsa_generate_checksum(&en->lsa, en->lsa_body);
OSPF_TRACE(D_EVENTS, "Advancing LSA: Type: %04x, Id: %R, Rt: %R, Seq: %08x",
en->lsa_type, en->lsa.id, en->lsa.rt, en->lsa.sn);
......@@ -238,7 +238,7 @@ ospf_do_originate_lsa(struct ospf_proto *p, struct top_hash_entry *en, void *lsa
en->lsa.age = 0;
en->init_age = 0;
en->inst_time = now;
lsasum_calculate(&en->lsa, en->lsa_body);
lsa_generate_checksum(&en->lsa, en->lsa_body);
OSPF_TRACE(D_EVENTS, "Originating LSA: Type: %04x, Id: %R, Rt: %R, Seq: %08x",
en->lsa_type, en->lsa.id, en->lsa.rt, en->lsa.sn);
......@@ -382,7 +382,7 @@ ospf_refresh_lsa(struct ospf_proto *p, struct top_hash_entry *en)
en->lsa.age = 0;
en->init_age = 0;
en->inst_time = now;
lsasum_calculate(&en->lsa, en->lsa_body);
lsa_generate_checksum(&en->lsa, en->lsa_body);
ospf_flood_lsa(p, en, NULL);
}
......
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