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net: don't accept non-left-contiguous netmasks

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A netmask that contains 1-bits after 0-bits (the 1-bits are not
contiguous on the left side) is invalid [1] [2].

The code before this PR used to parse and accept such
non-left-contiguous netmasks. However, a coming change that will alter
`CNetAddr::ip` to have flexible size would make juggling with such
netmasks more difficult, thus drop support for those.

[1] https://en.wikipedia.org/wiki/Classless_Inter-Domain_Routing#Subnet_masks
[2] https://tools.ietf.org/html/rfc4632#section-5.1
This commit is contained in:
Vasil Dimov
2020-08-24 21:03:31 +02:00
parent cb1ee1551c
commit 1ea57ad674
3 changed files with 48 additions and 54 deletions
Download Patch File Download Diff File Expand all files Collapse all files

90
src/netaddress.cpp
View File

@@ -789,9 +789,41 @@ CSubNet::CSubNet(const CNetAddr &addr, int32_t mask)
network.ip[x] &= netmask[x];
}
/**
* @returns The number of 1-bits in the prefix of the specified subnet mask. If
* the specified subnet mask is not a valid one, -1.
*/
static inline int NetmaskBits(uint8_t x)
{
switch(x) {
case 0x00: return 0;
case 0x80: return 1;
case 0xc0: return 2;
case 0xe0: return 3;
case 0xf0: return 4;
case 0xf8: return 5;
case 0xfc: return 6;
case 0xfe: return 7;
case 0xff: return 8;
default: return -1;
}
}
CSubNet::CSubNet(const CNetAddr &addr, const CNetAddr &mask)
{
valid = true;
// Check if `mask` contains 1-bits after 0-bits (which is an invalid netmask).
bool zeros_found = false;
for (size_t i = mask.IsIPv4() ? 12 : 0; i < sizeof(mask.ip); ++i) {
const int num_bits = NetmaskBits(mask.ip[i]);
if (num_bits == -1 || (zeros_found && num_bits != 0)) {
valid = false;
return;
}
if (num_bits < 8) {
zeros_found = true;
}
}
network = addr;
// Default to /32 (IPv4) or /128 (IPv6), i.e. match single address
memset(netmask, 255, sizeof(netmask));
@@ -828,62 +860,18 @@ bool CSubNet::Match(const CNetAddr &addr) const
return true;
}
/**
* @returns The number of 1-bits in the prefix of the specified subnet mask. If
* the specified subnet mask is not a valid one, -1.
*/
static inline int NetmaskBits(uint8_t x)
{
switch(x) {
case 0x00: return 0;
case 0x80: return 1;
case 0xc0: return 2;
case 0xe0: return 3;
case 0xf0: return 4;
case 0xf8: return 5;
case 0xfc: return 6;
case 0xfe: return 7;
case 0xff: return 8;
default: return -1;
}
}
std::string CSubNet::ToString() const
{
/* Parse binary 1{n}0{N-n} to see if mask can be represented as /n */
int cidr = 0;
bool valid_cidr = true;
int n = network.IsIPv4() ? 12 : 0;
for (; n < 16 && netmask[n] == 0xff; ++n)
cidr += 8;
if (n < 16) {
int bits = NetmaskBits(netmask[n]);
if (bits < 0)
valid_cidr = false;
else
cidr += bits;
++n;
}
for (; n < 16 && valid_cidr; ++n)
if (netmask[n] != 0x00)
valid_cidr = false;
uint8_t cidr = 0;
/* Format output */
std::string strNetmask;
if (valid_cidr) {
strNetmask = strprintf("%u", cidr);
} else {
if (network.IsIPv4())
strNetmask = strprintf("%u.%u.%u.%u", netmask[12], netmask[13], netmask[14], netmask[15]);
else
strNetmask = strprintf("%x:%x:%x:%x:%x:%x:%x:%x",
netmask[0] << 8 | netmask[1], netmask[2] << 8 | netmask[3],
netmask[4] << 8 | netmask[5], netmask[6] << 8 | netmask[7],
netmask[8] << 8 | netmask[9], netmask[10] << 8 | netmask[11],
netmask[12] << 8 | netmask[13], netmask[14] << 8 | netmask[15]);
for (size_t i = network.IsIPv4() ? 12 : 0; i < sizeof(netmask); ++i) {
if (netmask[i] == 0x00) {
break;
}
cidr += NetmaskBits(netmask[i]);
}
return network.ToString() + "/" + strNetmask;
return network.ToString() + strprintf("/%u", cidr);
}
bool CSubNet::IsValid() const