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in-addr-util: make in_addr_prefix_nth() always return valid prefix

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Previously, e.g. in_addr_prefix_nth(2400::1, prefixlen=32, nth=1)
does not return 2400:1:: but does 2400:1::1.
This commit is contained in:
Yu Watanabe
2021-02-17 22:57:37 +09:00
parent 7b6b05cff9
commit 9164338b2e
2 changed files with 26 additions and 30 deletions
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src/basic/in-addr-util.c
+18 -25
View File
@@ -199,8 +199,7 @@ int in_addr_prefix_next(int family, union in_addr_union *u, unsigned prefixlen)
* Calculates the nth prefix of size prefixlen starting from the address denoted by u.
*
* On success 0 will be returned and the calculated prefix will be available in
* u. In the case nth == 0 the input will be left unchanged and 0 will be returned.
* In case the calculation cannot be performed (invalid prefix length,
* u. In case the calculation cannot be performed (invalid prefix length,
* overflows would occur) -ERANGE is returned. If the address family given isn't
* supported -EAFNOSUPPORT will be returned.
*
@@ -217,9 +216,6 @@ int in_addr_prefix_nth(int family, union in_addr_union *u, unsigned prefixlen, u
if (prefixlen <= 0)
return -ERANGE;
if (nth == 0)
return 0;
if (family == AF_INET) {
uint32_t c, n, t;
@@ -242,38 +238,35 @@ int in_addr_prefix_nth(int family, union in_addr_union *u, unsigned prefixlen, u
}
if (family == AF_INET6) {
struct in6_addr result = {};
uint8_t overflow = 0;
uint64_t delta; /* this assumes that we only ever have to up to 1<<64 subnets */
unsigned start_byte = (prefixlen - 1) / 8;
bool overflow = false;
if (prefixlen > 128)
return -ERANGE;
/* First calculate what we have to add */
delta = nth << ((128 - prefixlen) % 8);
for (unsigned i = 16; i > 0; i--) {
unsigned j = i - 1;
unsigned t, j = i - 1, p = j * 8;
if (j <= start_byte) {
unsigned t, d;
if (p >= prefixlen) {
u->in6.s6_addr[j] = 0;
continue;
}
d = delta & 0xFF;
delta >>= 8;
if (prefixlen - p < 8) {
u->in6.s6_addr[j] &= 0xff << (8 - (prefixlen - p));
t = u->in6.s6_addr[j] + ((nth & 0xff) << (8 - (prefixlen - p)));
nth >>= prefixlen - p;
} else {
t = u->in6.s6_addr[j] + (nth & 0xff) + overflow;
nth >>= 8;
}
t = u->in6.s6_addr[j] + d + overflow;
overflow = t > UINT8_MAX ? t - UINT8_MAX : 0;
result.s6_addr[j] = (uint8_t) t;
} else
result.s6_addr[j] = u->in6.s6_addr[j];
overflow = t > UINT8_MAX;
u->in6.s6_addr[j] = (uint8_t) (t & 0xff);
}
if (overflow || delta != 0)
if (overflow || nth != 0)
return -ERANGE;
u->in6 = result;
return 0;
}