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Cygwin: bindresvport: Try hard to find unused port 

Workaround the problem that bind doesn't fail with EADDRINUSE
if a socket with the same local address is still in TIME_WAIT.

Use IP Helper functions to check if such a socket exist and don't
even try this port, if so.

Signed-off-by: Corinna Vinschen <corinna@vinschen.de>
This commit is contained in:
Corinna Vinschen 2018-02-05 21:05:09 +01:00
parent 2f61f65601
commit e9ff2d6978
2 changed files with 84 additions and 8 deletions
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2
winsup/cygwin/autoload.cc
View File

@ -573,6 +573,8 @@ LoadDLLfunc (GetIfEntry, 4, iphlpapi)
LoadDLLfunc (GetIpAddrTable, 12, iphlpapi)
LoadDLLfunc (GetIpForwardTable, 12, iphlpapi)
LoadDLLfunc (GetNetworkParams, 8, iphlpapi)
LoadDLLfunc (GetTcpTable, 12, iphlpapi)
LoadDLLfunc (GetTcp6Table, 12, iphlpapi)
LoadDLLfunc (GetUdpTable, 12, iphlpapi)
LoadDLLfunc (if_indextoname, 8, iphlpapi)
LoadDLLfunc (if_nametoindex, 4, iphlpapi)

90
winsup/cygwin/net.cc
View File

@ -2461,6 +2461,66 @@ if_freenameindex (struct if_nameindex *ptr)
#define PORT_HIGH (IPPORT_RESERVED - 1)
#define NUM_PORTS (PORT_HIGH - PORT_LOW + 1)
/* port is in host byte order */
static in_port_t
next_free_port (sa_family_t family, in_port_t in_port)
{
DWORD ret;
ULONG size = 0;
char *tab = NULL;
PMIB_TCPTABLE tab4 = NULL;
PMIB_TCP6TABLE tab6 = NULL;
/* Start testing with incoming port number. */
in_port_t tst_port = in_port;
in_port_t res_port = 0;
in_port_t tab_port;
do
{
if (family == AF_INET)
ret = GetTcpTable ((PMIB_TCPTABLE) tab, &size, TRUE);
else
ret = GetTcp6Table ((PMIB_TCP6TABLE) tab, &size, TRUE);
if (ret == ERROR_INSUFFICIENT_BUFFER)
tab = (char *) realloc (tab, size);
}
while (ret == ERROR_INSUFFICIENT_BUFFER);
tab4 = (PMIB_TCPTABLE) tab;
tab6 = (PMIB_TCP6TABLE) tab;
/* dwNumEntries has offset 0 in both structs. */
for (int idx = tab4->dwNumEntries - 1; idx >= 0; --idx)
{
if (family == AF_INET)
tab_port = ntohs (tab4->table[idx].dwLocalPort);
else
tab_port = ntohs (tab6->table[idx].dwLocalPort);
/* Skip table entries with too high port number. */
if (tab_port > tst_port)
continue;
/* Is the current port number free? */
if (tab_port < tst_port)
{
res_port = tst_port;
break;
}
/* Decrement port and handle underflow of the reserved area. */
if (--tst_port < PORT_LOW)
{
tst_port = PORT_HIGH;
idx = tab4->dwNumEntries;
}
/* Check if we're round to the incoming port. */
if (tst_port == in_port)
break;
}
free (tab);
return res_port;
}
extern "C" int
cygwin_bindresvport_sa (int fd, struct sockaddr *sa)
{
@ -2469,6 +2529,7 @@ cygwin_bindresvport_sa (int fd, struct sockaddr *sa)
struct sockaddr_in6 *sin6 = NULL;
socklen_t salen;
int ret = -1;
LONG port, next_port;
__try
{
@ -2507,21 +2568,34 @@ cygwin_bindresvport_sa (int fd, struct sockaddr *sa)
but that may lead to EADDRINUSE scenarios when calling bindresvport
on the client side. So we ignore any port value that the caller
supplies, just like glibc. */
LONG myport;
/* Note that repeating this loop NUM_PORTS times is arbitrary. The
job is mainly done by next_free_port() but it doesn't cover bound
sockets. And calling and checking GetTcpTable and subsequently
calling bind is inevitably racy. We have to continue if bind fails
with EADDRINUSE. */
for (int i = 0; i < NUM_PORTS; i++)
{
while ((myport = InterlockedExchange (
while ((port = InterlockedExchange (
&cygwin_shared->last_used_bindresvport, -1)) == -1)
yield ();
if (myport == 0 || --myport < PORT_LOW)
myport = PORT_HIGH;
InterlockedExchange (&cygwin_shared->last_used_bindresvport, myport);
next_port = port;
if (next_port == 0 || --next_port < PORT_LOW)
next_port = PORT_HIGH;
/* Returns 0 if no reserved port is free. */
next_port = next_free_port (sa->sa_family, next_port);
if (next_port)
port = next_port;
InterlockedExchange (&cygwin_shared->last_used_bindresvport, port);
if (next_port == 0)
{
set_errno (EADDRINUSE);
break;
}
if (sa->sa_family == AF_INET6)
sin6->sin6_port = htons (myport);
sin6->sin6_port = htons (port);
else
sin->sin_port = htons (myport);
sin->sin_port = htons (port);
if (!(ret = fh->bind (sa, salen)))
break;
if (get_errno () != EADDRINUSE && get_errno () != EINVAL)