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Virtual: fix race condition in DHCP server which resulted in multiple clients receiving the same IP

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A race condition in the DHCP server caused it to offer the same IP address to multiple clients when they connected at the same time, because an offered IP address was considered free until the final step (DHCP_ACK).

This commit introduces a list to keep track of the pending leases created during DHCP_OFFER, so that an IP address is guaranteed to be offered to a single client.
This commit is contained in:
Davide Beatrici 2019-07-13 23:29:16 +02:00
parent 831c907512
commit d6cf1b85a9
2 changed files with 113 additions and 20 deletions
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130
src/Cedar/Virtual.c
View File

@ -8956,8 +8956,8 @@ void FreeDhcpServer(VH *v)
return;
}
// Remove the all lease entries
for (i = 0;i < LIST_NUM(v->DhcpLeaseList);i++)
// Empty the leases lists
for (i = 0; i < LIST_NUM(v->DhcpLeaseList); ++i)
{
DHCP_LEASE *d = LIST_DATA(v->DhcpLeaseList, i);
FreeDhcpLease(d);
@ -8965,6 +8965,15 @@ void FreeDhcpServer(VH *v)
ReleaseList(v->DhcpLeaseList);
v->DhcpLeaseList = NULL;
for (i = 0; i < LIST_NUM(v->DhcpPendingLeaseList); ++i)
{
DHCP_LEASE *d = LIST_DATA(v->DhcpPendingLeaseList, i);
FreeDhcpLease(d);
}
ReleaseList(v->DhcpPendingLeaseList);
v->DhcpPendingLeaseList = NULL;
}
// Initialize the DHCP server
@ -8978,6 +8987,29 @@ void InitDhcpServer(VH *v)
// Create a list
v->DhcpLeaseList = NewList(CompareDhcpLeaseList);
v->DhcpPendingLeaseList = NewList(CompareDhcpLeaseList);
}
// Search for a pending DHCP lease item by the IP address
DHCP_LEASE *SearchDhcpPendingLeaseByIp(VH *v, UINT ip)
{
UINT i;
// Validate arguments
if (v == NULL)
{
return NULL;
}
for (i = 0; i < LIST_NUM(v->DhcpPendingLeaseList); ++i)
{
DHCP_LEASE *d = LIST_DATA(v->DhcpPendingLeaseList, i);
if (d->IpAddress == ip)
{
return d;
}
}
return NULL;
}
// Search for a DHCP lease item by the IP address
@ -8990,7 +9022,7 @@ DHCP_LEASE *SearchDhcpLeaseByIp(VH *v, UINT ip)
return NULL;
}
for (i = 0;i < LIST_NUM(v->DhcpLeaseList);i++)
for (i = 0; i < LIST_NUM(v->DhcpLeaseList); ++i)
{
DHCP_LEASE *d = LIST_DATA(v->DhcpLeaseList, i);
if (d->IpAddress == ip)
@ -9002,6 +9034,22 @@ DHCP_LEASE *SearchDhcpLeaseByIp(VH *v, UINT ip)
return NULL;
}
// Search for a pending DHCP lease item by the MAC address
DHCP_LEASE *SearchDhcpPendingLeaseByMac(VH *v, UCHAR *mac)
{
DHCP_LEASE *d, t;
// Validate arguments
if (v == NULL || mac == NULL)
{
return NULL;
}
Copy(&t.MacAddress, mac, 6);
d = Search(v->DhcpPendingLeaseList, &t);
return d;
}
// Search for a DHCP lease item by the MAC address
DHCP_LEASE *SearchDhcpLeaseByMac(VH *v, UCHAR *mac)
{
@ -9099,9 +9147,8 @@ void PollingDhcpServer(VH *v)
}
v->LastDhcpPolling = v->Now;
// Remove expired entries
FIRST_LIST:
for (i = 0;i < LIST_NUM(v->DhcpLeaseList);i++)
LIST_CLEANUP:
for (i = 0; i < LIST_NUM(v->DhcpLeaseList); ++i)
{
DHCP_LEASE *d = LIST_DATA(v->DhcpLeaseList, i);
@ -9109,7 +9156,21 @@ FIRST_LIST:
{
FreeDhcpLease(d);
Delete(v->DhcpLeaseList, d);
goto FIRST_LIST;
goto LIST_CLEANUP;
}
}
PENDING_LIST_CLEANUP:
// Remove expired entries
for (i = 0; i < LIST_NUM(v->DhcpPendingLeaseList); ++i)
{
DHCP_LEASE *d = LIST_DATA(v->DhcpPendingLeaseList, i);
if (d->ExpireTime < v->Now)
{
FreeDhcpLease(d);
Delete(v->DhcpPendingLeaseList, d);
goto PENDING_LIST_CLEANUP;
}
}
}
@ -9151,6 +9212,11 @@ UINT ServeDhcpDiscover(VH *v, UCHAR *mac, UINT request_ip)
{
// IP address is specified
DHCP_LEASE *d = SearchDhcpLeaseByIp(v, request_ip);
if (d == NULL)
{
d = SearchDhcpPendingLeaseByIp(v, request_ip);
}
if (d != NULL)
{
// If an entry for the same IP address already exists,
@ -9187,6 +9253,11 @@ UINT ServeDhcpDiscover(VH *v, UCHAR *mac, UINT request_ip)
// If there is any entry with the same MAC address
// that are already registered, use it with priority
DHCP_LEASE *d = SearchDhcpLeaseByMac(v, mac);
if (d == NULL)
{
d = SearchDhcpPendingLeaseByMac(v, mac);
}
if (d != NULL)
{
// Examine whether the found IP address is in the allocation region
@ -9234,7 +9305,7 @@ UINT GetFreeDhcpIpAddress(VH *v)
for (i = ip_start; i <= ip_end;i++)
{
UINT ip = Endian32(i);
if (SearchDhcpLeaseByIp(v, ip) == NULL)
if (SearchDhcpLeaseByIp(v, ip) == NULL && SearchDhcpPendingLeaseByIp(v, ip) == NULL)
{
// A free IP address is found
return ip;
@ -9284,7 +9355,7 @@ UINT GetFreeDhcpIpAddressByRandom(VH *v, UCHAR *mac)
new_ip = Endian32(ip_start + (rand_int % (ip_end - ip_start + 1)));
if (SearchDhcpLeaseByIp(v, new_ip) == NULL)
if (SearchDhcpLeaseByIp(v, new_ip) == NULL && SearchDhcpPendingLeaseByIp(v, new_ip) == NULL)
{
// A free IP address is found
return new_ip;
@ -9401,8 +9472,9 @@ void VirtualDhcpServer(VH *v, PKT *p)
if (opt->Opcode == DHCP_REQUEST)
{
DHCP_LEASE *d;
char mac[MAX_SIZE];
char str[MAX_SIZE];
char client_mac[MAX_SIZE];
char client_ip[MAX_SIZE];
// Remove old records with the same IP address
d = SearchDhcpLeaseByIp(v, ip);
if (d != NULL)
@ -9411,17 +9483,22 @@ void VirtualDhcpServer(VH *v, PKT *p)
Delete(v->DhcpLeaseList, d);
}
d = SearchDhcpPendingLeaseByIp(v, ip);
if (d != NULL)
{
FreeDhcpLease(d);
Delete(v->DhcpPendingLeaseList, d);
}
// Create a new entry
d = NewDhcpLease(v->DhcpExpire, p->MacAddressSrc,
ip, v->DhcpMask,
opt->Hostname);
d = NewDhcpLease(v->DhcpExpire, p->MacAddressSrc, ip, v->DhcpMask, opt->Hostname);
d->Id = ++v->DhcpId;
Add(v->DhcpLeaseList, d);
MacToStr(mac, sizeof(mac), d->MacAddress);
IPToStr32(str, sizeof(str), d->IpAddress);
MacToStr(client_mac, sizeof(client_mac), d->MacAddress);
IPToStr32(client_ip, sizeof(client_ip), d->IpAddress);
NLog(v, "LH_NAT_DHCP_CREATED", d->Id, mac, str, d->Hostname, v->DhcpExpire / 1000);
NLog(v, "LH_NAT_DHCP_CREATED", d->Id, client_mac, client_ip, d->Hostname, v->DhcpExpire / 1000);
}
// Respond
@ -9510,12 +9587,25 @@ void VirtualDhcpServer(VH *v, PKT *p)
char client_mac[MAX_SIZE];
char client_ip[64];
IP ips;
BinToStr(client_mac, sizeof(client_mac), p->MacAddressSrc, 6);
UINTToIP(&ips, ip);
IPToStr(client_ip, sizeof(client_ip), &ips);
Debug("DHCP %s : %s given %s\n",
ret.Opcode == DHCP_OFFER ? "DHCP_OFFER" : "DHCP_ACK",
client_mac, client_ip);
if (ret.Opcode == DHCP_OFFER)
{
// DHCP_OFFER
DHCP_LEASE *d = NewDhcpLease(5000, p->MacAddressSrc, ip, v->DhcpMask, opt->Hostname);
d->Id = LIST_NUM(v->DhcpPendingLeaseList);
Add(v->DhcpPendingLeaseList, d);
Debug("VirtualDhcpServer(): %s has been marked as pending for %s\n", client_ip, client_mac);
}
else
{
// DHCP_ACK
Debug("VirtualDhcpServer(): %s has been assigned to %s\n", client_ip, client_mac);
}
}
// Build a DHCP option

3
src/Cedar/Virtual.h
View File

@ -296,6 +296,7 @@ struct VH
UINT DhcpDns2; // DNS server address 2
char DhcpDomain[MAX_HOST_NAME_LEN + 1]; // Assigned domain name
LIST *DhcpLeaseList; // DHCP lease list
LIST *DhcpPendingLeaseList; // Pending DHCP lease list
UINT64 LastDhcpPolling; // Time which the DHCP list polled last
bool SaveLog; // Save a log
DHCP_CLASSLESS_ROUTE_TABLE PushRoute; // Pushing routing table
@ -511,7 +512,9 @@ int CompareDhcpLeaseList(void *p1, void *p2);
DHCP_LEASE *NewDhcpLease(UINT expire, UCHAR *mac_address, UINT ip, UINT mask, char *hostname);
void FreeDhcpLease(DHCP_LEASE *d);
DHCP_LEASE *SearchDhcpLeaseByMac(VH *v, UCHAR *mac);
DHCP_LEASE *SearchDhcpPendingLeaseByMac(VH *v, UCHAR *mac);
DHCP_LEASE *SearchDhcpLeaseByIp(VH *v, UINT ip);
DHCP_LEASE *SearchDhcpPendingLeaseByIp(VH *v, UINT ip);
UINT ServeDhcpDiscover(VH *v, UCHAR *mac, UINT request_ip);
UINT GetFreeDhcpIpAddress(VH *v);
UINT GetFreeDhcpIpAddressByRandom(VH *v, UCHAR *mac);