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mirror_frr/tests/test-checksum.c
Paul Jakma 5d4b8cf2fa [lib] Switch Fletcher checksum back to old ospfd version 
* lib/checksum.c: (fletcher_checksum) Switch the second phase of the checksum
  back to the old ospfd logic.

  The isisd-derived version:

  a) is very hard to follow
  b) had some kind of subtle bug that caused it be wrong when c0=0 and c1=254
     (potentially fixable by doing the mods before adjusting x and y)

  Additionally:

  - explicitely cast expressions using non-internal variables to int, to ensure
    the result is signed.
  - defensively change the length argument to 'size_t', to ensure the code
    works with that argument being unsigned..

  Thanks to Joakim Tjernlund for the investigative work into this bug.

* tests/test-checksum.c: new file to exercise the checksum code.
2008-11-16 18:47:02 +00:00

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#include <zebra.h>
#include <stdlib.h>
#include <time.h>
#include "checksum.h"
struct thread_master *master;
struct acc_vals {
int c0;
int c1;
};
struct csum_vals {
struct acc_vals a;
int x;
int y;
};
static struct csum_vals ospfd_vals, isisd_vals;
typedef size_t testsz_t;
typedef uint16_t testoff_t;
/* Fletcher Checksum -- Refer to RFC1008. */
#define MODX 4102
/* Accumulator phase of checksum */
static
struct acc_vals
accumulate (u_char *buffer, testsz_t len, testoff_t off)
{
u_int8_t *p;
u_int16_t *csum;
int i, init_len, partial_len;
struct acc_vals ret;
csum = (u_int16_t *) (buffer + off);
*(csum) = 0;
p = buffer;
ret.c0 = 0;
ret.c1 = 0;
init_len = len;
while (len != 0)
{
partial_len = MIN(len, MODX);
for (i = 0; i < partial_len; i++)
{
ret.c0 = ret.c0 + *(p++);
ret.c1 += ret.c0;
}
ret.c0 = ret.c0 % 255;
ret.c1 = ret.c1 % 255;
len -= partial_len;
}
return ret;
}
/* The final reduction phase.
* This one should be the original ospfd version
*/
static u_int16_t
reduce_ospfd (struct csum_vals *vals, testsz_t len, testoff_t off)
{
#define x vals->x
#define y vals->y
#define c0 vals->a.c0
#define c1 vals->a.c1
x = ((len - off - 1) * c0 - c1) % 255;
if (x <= 0)
x += 255;
y = 510 - c0 - x;
if (y > 255)
y -= 255;
/* take care endian issue. */
return htons ((x << 8) + y);
#undef x
#undef y
#undef c0
#undef c1
}
/* slightly different concatenation */
static u_int16_t
reduce_ospfd1 (struct csum_vals *vals, testsz_t len, testoff_t off)
{
#define x vals->x
#define y vals->y
#define c0 vals->a.c0
#define c1 vals->a.c1
x = ((len - off - 1) * c0 - c1) % 255;
if (x <= 0)
x += 255;
y = 510 - c0 - x;
if (y > 255)
y -= 255;
/* take care endian issue. */
return htons ((x << 8) | (y & 0xff));
#undef x
#undef y
#undef c0
#undef c1
}
/* original isisd version */
static u_int16_t
reduce_isisd (struct csum_vals *vals, testsz_t len, testoff_t off)
{
#define x vals->x
#define y vals->y
#define c0 vals->a.c0
#define c1 vals->a.c1
u_int32_t mul;
mul = (len - off)*(c0);
x = mul - c0 - c1;
y = c1 - mul - 1;
if (y > 0)
y++;
if (x < 0)
x--;
x %= 255;
y %= 255;
if (x == 0)
x = 255;
if (y == 0)
y = 1;
return htons ((x << 8) | (y & 0xff));
#undef x
#undef y
#undef c0
#undef c1
}
/* Is the -1 in y wrong perhaps? */
static u_int16_t
reduce_isisd_yfix (struct csum_vals *vals, testsz_t len, testoff_t off)
{
#define x vals->x
#define y vals->y
#define c0 vals->a.c0
#define c1 vals->a.c1
u_int32_t mul;
mul = (len - off)*(c0);
x = mul - c0 - c1;
y = c1 - mul;
if (y > 0)
y++;
if (x < 0)
x--;
x %= 255;
y %= 255;
if (x == 0)
x = 255;
if (y == 0)
y = 1;
return htons ((x << 8) | (y & 0xff));
#undef x
#undef y
#undef c0
#undef c1
}
/* Move the mods yp */
static u_int16_t
reduce_isisd_mod (struct csum_vals *vals, testsz_t len, testoff_t off)
{
#define x vals->x
#define y vals->y
#define c0 vals->a.c0
#define c1 vals->a.c1
u_int32_t mul;
mul = (len - off)*(c0);
x = mul - c1 - c0;
y = c1 - mul - 1;
x %= 255;
y %= 255;
if (y > 0)
y++;
if (x < 0)
x--;
if (x == 0)
x = 255;
if (y == 0)
y = 1;
return htons ((x << 8) | (y & 0xff));
#undef x
#undef y
#undef c0
#undef c1
}
/* Move the mods up + fix y */
static u_int16_t
reduce_isisd_mody (struct csum_vals *vals, testsz_t len, testoff_t off)
{
#define x vals->x
#define y vals->y
#define c0 vals->a.c0
#define c1 vals->a.c1
u_int32_t mul;
mul = (len - off)*(c0);
x = mul - c0 - c1;
y = c1 - mul;
x %= 255;
y %= 255;
if (y > 0)
y++;
if (x < 0)
x--;
if (x == 0)
x = 255;
if (y == 0)
y = 1;
return htons ((x << 8) | (y & 0xff));
#undef x
#undef y
#undef c0
#undef c1
}
struct reductions_t {
const char *name;
u_int16_t (*f) (struct csum_vals *, testsz_t, testoff_t);
} reducts[] = {
{ .name = "ospfd", .f = reduce_ospfd },
{ .name = "ospfd-1", .f = reduce_ospfd1 },
{ .name = "isisd", .f = reduce_isisd },
{ .name = "isisd-yfix", .f = reduce_isisd_yfix },
{ .name = "isisd-mod", .f = reduce_isisd_mod },
{ .name = "isisd-mody", .f = reduce_isisd_mody },
{ NULL, NULL },
};
/* The original ospfd checksum */
static u_int16_t
ospfd_checksum (u_char *buffer, testsz_t len, testoff_t off)
{
u_char *sp, *ep, *p, *q;
int c0 = 0, c1 = 0;
int x, y;
u_int16_t checksum, *csum;
csum = (u_int16_t *) (buffer + off);
*(csum) = 0;
sp = buffer;
for (ep = sp + len; sp < ep; sp = q)
{
q = sp + MODX;
if (q > ep)
q = ep;
for (p = sp; p < q; p++)
{
c0 += *p;
c1 += c0;
}
c0 %= 255;
c1 %= 255;
}
ospfd_vals.a.c0 = c0;
ospfd_vals.a.c1 = c1;
//printf ("%s: len %u, off %u, c0 %d, c1 %d\n",
// __func__, len, off, c0, c1);
x = ((int)(len - off - 1) * (int)c0 - (int)c1) % 255;
if (x <= 0)
x += 255;
y = 510 - c0 - x;
if (y > 255)
y -= 255;
ospfd_vals.x = x;
ospfd_vals.y = y;
buffer[off] = x;
buffer[off + 1] = y;
/* take care endian issue. */
checksum = htons ((x << 8) | (y & 0xff));
return (checksum);
}
/* the original, broken isisd checksum */
static u_int16_t
iso_csum_create (u_char * buffer, testsz_t len, testoff_t off)
{
u_int8_t *p;
int x;
int y;
u_int32_t mul;
u_int32_t c0;
u_int32_t c1;
u_int16_t checksum, *csum;
int i, init_len, partial_len;
checksum = 0;
csum = (u_int16_t *) (buffer + off);
*(csum) = checksum;
p = buffer;
c0 = 0;
c1 = 0;
init_len = len;
while (len != 0)
{
partial_len = MIN(len, MODX);
for (i = 0; i < partial_len; i++)
{
c0 = c0 + *(p++);
c1 += c0;
}
c0 = c0 % 255;
c1 = c1 % 255;
len -= partial_len;
}
isisd_vals.a.c0 = c0;
isisd_vals.a.c1 = c1;
mul = (init_len - off) * c0;
x = mul - c1 - c0;
y = c1 - mul - 1;
if (y > 0)
y++;
if (x < 0)
x--;
x %= 255;
y %= 255;
if (x == 0)
x = 255;
if (y == 0)
y = 1;
isisd_vals.x = x;
isisd_vals.y = y;
checksum = htons((x << 8) | (y & 0xFF));
*(csum) = checksum;
/* return the checksum for user usage */
return checksum;
}
static int
verify (u_char * buffer, testsz_t len)
{
u_int8_t *p;
u_int32_t c0;
u_int32_t c1;
u_int16_t checksum;
int i, partial_len;
p = buffer;
checksum = 0;
c0 = 0;
c1 = 0;
while (len)
{
partial_len = MIN(len, 5803);
for (i = 0; i < partial_len; i++)
{
c0 = c0 + *(p++);
c1 += c0;
}
c0 = c0 % 255;
c1 = c1 % 255;
len -= partial_len;
}
if (c0 == 0 && c1 == 0)
return 0;
return 1;
}
int
main(int argc, char **argv)
{
/* 60017 65629 702179 */
#define MAXDATALEN 60017
#define BUFSIZE MAXDATALEN + sizeof(u_int16_t)
u_char buffer[BUFSIZE];
int exercise = 0;
#define EXERCISESTEP 257
srandom (time (NULL));
while (1) {
u_int16_t ospfd, isisd, lib;
exercise += EXERCISESTEP;
exercise %= MAXDATALEN;
for (int i = 0; i < exercise; i += sizeof (long int)) {
long int rand = random ();
for (int j = sizeof (long int); j > 0; j--)
buffer[i + (sizeof (long int) - j)] = (rand >> (j * 8)) & 0xff;
}
ospfd = ospfd_checksum (buffer, exercise + sizeof(u_int16_t), exercise);
if (verify (buffer, exercise + sizeof(u_int16_t)))
printf ("verify: ospfd failed\n");
isisd = iso_csum_create (buffer, exercise + sizeof(u_int16_t), exercise);
if (verify (buffer, exercise + sizeof(u_int16_t)))
printf ("verify: isisd failed\n");
lib = fletcher_checksum (buffer, exercise + sizeof(u_int16_t), exercise);
if (verify (buffer, exercise + sizeof(u_int16_t)))
printf ("verify: lib failed\n");
if (ospfd != lib) {
printf ("Mismatch in values at size %u\n"
"ospfd: 0x%04x\tc0: %d\tc1: %d\tx: %d\ty: %d\n"
"isisd: 0x%04x\tc0: %d\tc1: %d\tx: %d\ty: %d\n"
"lib: 0x%04x\n",
exercise,
ospfd, ospfd_vals.a.c0, ospfd_vals.a.c1, ospfd_vals.x, ospfd_vals.y,
isisd, isisd_vals.a.c0, isisd_vals.a.c1, isisd_vals.x, isisd_vals.y,
lib
);
/* Investigate reduction phase discrepencies */
if (ospfd_vals.a.c0 == isisd_vals.a.c0
&& ospfd_vals.a.c1 == isisd_vals.a.c1) {
printf ("\n");
for (int i = 0; reducts[i].name != NULL; i++) {
ospfd = reducts[i].f (&ospfd_vals,
exercise + sizeof (u_int16_t),
exercise);
printf ("%20s: x: %02x, y %02x, checksum 0x%04x\n",
reducts[i].name, ospfd_vals.x & 0xff, ospfd_vals.y & 0xff, ospfd);
}
}
printf ("\n u_char testdata [] = {\n ");
for (int i = 0; i < exercise; i++) {
printf ("0x%02x,%s",
buffer[i],
(i + 1) % 8 ? " " : "\n ");
}
printf ("\n}\n");
exit (1);
}
}
}
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