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connect: defer port selection until connect() time

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If supported, defer port selection until connect() time
if --interface is given and source port is 0.

Reproducer:

* start fast webserver on port 80
* starve system of ephemeral ports
$  sysctl net.ipv4.ip_local_port_range="60990 60999"

* start a curl/libcurl "crawler"
$curl --keepalive --parallel --parallel-immediate --head --interface
127.0.0.2 "http://127.0.0.[1-254]/file[001-002].txt"

current result:
(possible some successful data)
curl: (45) bind failed with errno 98: Address already in use

result after patch:
(complete success or few connections failing, higlhy depending on load)

Fail only when all the possible 4-tuple combinations are exhausted,
which is impossible to do when port is selected at bind() time becuse
the kernel does not know if socket will be listen()'ed on or connect'ed
yet.

Closes #6295
This commit is contained in:
Cristian Rodríguez 2020-12-09 16:30:29 -03:00 committed by Daniel Stenberg
parent 8a10abaf85
commit 25b4e158e9
No known key found for this signature in database
GPG Key ID: 5CC908FDB71E12C2
1 changed files with 6 additions and 1 deletions
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7
lib/connect.c
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@ -256,6 +256,9 @@ static CURLcode bindlocal(struct connectdata *conn,
int portnum = data->set.localportrange;
const char *dev = data->set.str[STRING_DEVICE];
int error;
#ifdef IP_BIND_ADDRESS_NO_PORT
int on = 1;
#endif
/*************************************************************
* Select device to bind socket to
@ -441,7 +444,9 @@ static CURLcode bindlocal(struct connectdata *conn,
sizeof_sa = sizeof(struct sockaddr_in);
}
}
#ifdef IP_BIND_ADDRESS_NO_PORT
setsockopt(sockfd, SOL_IP, IP_BIND_ADDRESS_NO_PORT, &on, sizeof(on));
#endif
for(;;) {
if(bind(sockfd, sock, sizeof_sa) >= 0) {
/* we succeeded to bind */