https://sourceware.org/git/gitweb.cgi?p=newlib-cygwin.git;h=e9ff2d697871eb78f7a4bc246868c855c052a859
commit e9ff2d697871eb78f7a4bc246868c855c052a859 Author: Corinna Vinschen <[email protected]> Date: Mon Feb 5 21:05:09 2018 +0100 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 <[email protected]> Diff: --- winsup/cygwin/autoload.cc | 2 ++ winsup/cygwin/net.cc | 90 ++++++++++++++++++++++++++++++++++++++++++----- 2 files changed, 84 insertions(+), 8 deletions(-) diff --git a/winsup/cygwin/autoload.cc b/winsup/cygwin/autoload.cc index 349f5e7..199821d 100644 --- a/winsup/cygwin/autoload.cc +++ b/winsup/cygwin/autoload.cc @@ -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) diff --git a/winsup/cygwin/net.cc b/winsup/cygwin/net.cc index cd43347..3fadb2b 100644 --- a/winsup/cygwin/net.cc +++ b/winsup/cygwin/net.cc @@ -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)
