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Can't make SFTP with proxy tunnel in HTTPS #4295

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Koaxiel opened this issue Sep 4, 2019 · 8 comments
Closed

Can't make SFTP with proxy tunnel in HTTPS #4295

Koaxiel opened this issue Sep 4, 2019 · 8 comments

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@Koaxiel
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@Koaxiel Koaxiel commented Sep 4, 2019

I have an issue when I use curl to fetch some files with using SFTP protocol via the usage of a HTTP proxy via https (when I use http I don't have this issue):

curl -vvv --proxy https://myproxy.domain.org:443 --proxy-user login:password --user demo:password --insecure sftp://test.rebex.net/readme.txt

*   Trying 10.225.9.29:443...
* TCP_NODELAY set
* Connected to myproxy.domain.org (10.225.9.29) port 443 (#0)
* successfully set certificate verify locations:
*   CAfile: /etc/ssl/certs/ca-certificates.crt
  CApath: none
* TLSv1.3 (OUT), TLS handshake, Client hello (1):
* TLSv1.3 (IN), TLS handshake, Server hello (2):
* TLSv1.2 (IN), TLS handshake, Certificate (11):
* TLSv1.2 (IN), TLS handshake, Server finished (14):
* TLSv1.2 (OUT), TLS handshake, Client key exchange (16):
* TLSv1.2 (OUT), TLS change cipher, Change cipher spec (1):
* TLSv1.2 (OUT), TLS handshake, Finished (20):
* TLSv1.2 (IN), TLS handshake, Finished (20):
* SSL connection using TLSv1.2 / AES256-GCM-SHA384
* Proxy certificate:
*  subject: C=FR; L=Paris; O=Criteo SA; OU=CRITEO SA; CN=myproxy.domain.org
*  start date: Jul  3 00:00:00 2019 GMT
*  expire date: Jul  7 12:00:00 2020 GMT
*  subjectAltName: host "myproxy.domain.org" matched cert's "myproxy.domain.org"
*  issuer: C=US; O=DigiCert Inc; CN=DigiCert SHA2 Secure Server CA
*  SSL certificate verify ok.
* allocate connect buffer!
* Establish HTTP proxy tunnel to test.rebex.net:22
* Proxy auth using Basic with user 'login'
* Server auth using Basic with user 'demo'
> CONNECT test.rebex.net:22 HTTP/1.1
> Host: test.rebex.net:22
> Proxy-Authorization: Basic c3ZjLW5ldHdvcmtwgh78eTo6SDZFRTJhQjI9ZjpnFhiJIDBvLgI==
> User-Agent: curl/7.65.3
> Proxy-Connection: Keep-Alive
> 
< HTTP/1.1 200 Connection established
< 
* Proxy replied 200 to CONNECT request
* CONNECT phase completed!
* CONNECT phase completed!
* Failure establishing ssh session: -2, Failed getting banner
* Closing connection 0
* TLSv1.2 (OUT), TLS alert, close notify (256):
curl: (2) Failure establishing ssh session: -2, Failed getting banner

The same but I connect to the proxy via http:

curl -vvv --proxy http://myproxy.domain.org:80 --proxy-user login:password --user demo:password --insecure sftp://test.rebex.net/readme.txt

*   Trying 10.225.9.29:80...
* TCP_NODELAY set
* Connected to myproxy.domain.org (10.225.9.29) port 80 (#0)
* allocate connect buffer!
* Establish HTTP proxy tunnel to test.rebex.net:22
* Proxy auth using Basic with user 'login'
* Server auth using Basic with user 'demo'
> CONNECT test.rebex.net:22 HTTP/1.1
> Host: test.rebex.net:22
> Proxy-Authorization: Basic c3ZjLW5ldHdvcmtwgh78eTo6SDZFRTJhQjI9ZjpnFhiJIDBvLgI==
> User-Agent: curl/7.65.3
> Proxy-Connection: Keep-Alive
> 
< HTTP/1.1 200 Connection established
< 
* Proxy replied 200 to CONNECT request
* CONNECT phase completed!
* CONNECT phase completed!
* SSH MD5 fingerprint: 0361c498f1ff7d239751071388b8c555
* SSH authentication methods available: password,keyboard-interactive,publickey
* Using SSH private key file '/home/toto/.ssh/id_rsa'
* SSH public key authentication failed: Unable to extract public key from private key file: Wrong passphrase or invalid/unrecognized private key file format
* Initialized password authentication
* Authentication complete
Welcome,

you are connected to an FTP or SFTP server used for testing purposes by Rebex FTP/SSL or Rebex SFTP sample code.
Only read access is allowed and the FTP download speed is limited to 16KBps.

For infomation about Rebex FTP/SSL, Rebex SFTP and other Rebex .NET components, please visit our website at http://www.rebex.net/

For feedback and support, contact support@rebex.net

Thanks!
* Connection #0 to host myproxy.domain.org left intact

I haven't issue when I connect to the proxy via https and I replace SFTP by FTP or FTPS.

curl/libcurl version

curl 7.65.3 (x86_64-pc-linux-gnu) libcurl/7.65.3 OpenSSL/1.1.1c zlib/1.2.11 libidn2/2.2.0 libpsl/0.21.0 (+libidn2/2.2.0) libssh2/1.8.2 nghttp2/1.39.2
Release-Date: 2019-07-19
Protocols: dict file ftp ftps gopher http https imap imaps pop3 pop3s rtsp scp sftp smb smbs smtp smtps telnet tftp 
Features: AsynchDNS GSS-API HTTP2 HTTPS-proxy IDN IPv6 Kerberos Largefile libz NTLM NTLM_WB PSL SPNEGO SSL TLS-SRP UnixSockets

operating system

Arch Linux

@bagder
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@bagder bagder commented Dec 16, 2019

I cannot reproduce using plain curl from Debian:

$ curl -x proxy:80 -p sftp://machine/ -vk -u user:password
drwx------   22 root     root         4096 Dec 16 11:10 root
drwxr-xr-x    3 root     root         4096 Dec 10 09:59 boot
drwxr-xr-x   19 root     root         3740 Dec 16 11:33 dev
drwxr-xr-x    4 root     root         4096 Oct  5  2013 mnt
lrwxrwxrwx    1 root     root           29 Dec 10 09:59 initrd.img.old -> boot/initrd.img-5.3.0-2-amd64
...
$ curl -V
curl 7.67.0 (x86_64-pc-linux-gnu) libcurl/7.67.0 OpenSSL/1.1.1d zlib/1.2.11 brotli/1.0.7 libidn2/2.2.0 libpsl/0.20.2 (+libidn2/2.0.5) libssh2/1.8.0 nghttp2/1.40.0 librtmp/2.3
Release-Date: 2019-11-06
Protocols: dict file ftp ftps gopher http https imap imaps ldap ldaps pop3 pop3s rtmp rtsp scp sftp smb smbs smtp smtps telnet tftp 
Features: AsynchDNS brotli GSS-API HTTP2 HTTPS-proxy IDN IPv6 Kerberos Largefile libz NTLM NTLM_WB PSL SPNEGO SSL TLS-SRP UnixSockets
@bagder
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@bagder bagder commented Dec 16, 2019

Although I note now that I didn't use a HTTPS proxy, just a plain HTTP.... Does that make a difference to you @Koaxiel ?

@Koaxiel
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@Koaxiel Koaxiel commented Dec 17, 2019

Exactly, the issue occurs only when I connect to the proxy via HTTPS.

@bagder
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@bagder bagder commented Dec 17, 2019

and it works if you use a HTTP proxy? Yes you already wrote that...

@bagder
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@bagder bagder commented Dec 17, 2019

Reproduced with stunnel, a local HTTP proxy (on port 80) and a local SFTP server:

$ stunnel -p $HOME/src/curl/tests/stunnel.pem -f -d 8843 -r 80 -P `pwd`/stunnel.pid &
$ ./src/curl -x https://localhost:8843 -p sftp://machine/ -vk --proxy-insecure
@shilpa-gupta
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@shilpa-gupta shilpa-gupta commented Feb 27, 2020

I am facing similar problem. Was there any resolution to this?

@bagder
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@bagder bagder commented Feb 28, 2020

This issue is still open because it has not been resolved, and in fact there hasn't even been a PR filed for it...

@FBNeal
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@FBNeal FBNeal commented Jun 1, 2020

Possibly naive observation: it looks like the problem here is that the socket passed to the SSH library with an HTTPS proxy is a TLS socket. There's code intended to override Curl_write / Curl_read for the sockets:

curl/lib/vssh/libssh2.c

Lines 3019 to 3026 in 842f73d

if(conn->handler->protocol & CURLPROTO_SCP) {
conn->recv[FIRSTSOCKET] = scp_recv;
conn->send[FIRSTSOCKET] = scp_send;
}
else {
conn->recv[FIRSTSOCKET] = sftp_recv;
conn->send[FIRSTSOCKET] = sftp_send;
}

curl/lib/vssh/libssh2.c

Lines 3354 to 3402 in 842f73d

/* return number of sent bytes */
static ssize_t sftp_send(struct connectdata *conn, int sockindex,
const void *mem, size_t len, CURLcode *err)
{
ssize_t nwrite; /* libssh2_sftp_write() used to return size_t in 0.14
but is changed to ssize_t in 0.15. These days we don't
support libssh2 0.15*/
(void)sockindex;
nwrite = libssh2_sftp_write(conn->proto.sshc.sftp_handle, mem, len);
ssh_block2waitfor(conn, (nwrite == LIBSSH2_ERROR_EAGAIN)?TRUE:FALSE);
if(nwrite == LIBSSH2_ERROR_EAGAIN) {
*err = CURLE_AGAIN;
nwrite = 0;
}
else if(nwrite < LIBSSH2_ERROR_NONE) {
*err = libssh2_session_error_to_CURLE((int)nwrite);
nwrite = -1;
}
return nwrite;
}
/*
* Return number of received (decrypted) bytes
* or <0 on error
*/
static ssize_t sftp_recv(struct connectdata *conn, int sockindex,
char *mem, size_t len, CURLcode *err)
{
ssize_t nread;
(void)sockindex;
nread = libssh2_sftp_read(conn->proto.sshc.sftp_handle, mem, len);
ssh_block2waitfor(conn, (nread == LIBSSH2_ERROR_EAGAIN)?TRUE:FALSE);
if(nread == LIBSSH2_ERROR_EAGAIN) {
*err = CURLE_AGAIN;
nread = -1;
}
else if(nread < 0) {
*err = libssh2_session_error_to_CURLE((int)nread);
}
return nread;
}

But that wouldn't take into account TLS on the underlying socket. The basic send/recv functions in libssh2, at least, expect to be able to just use send/recv in order to send/receive packets.

https://github.com/libssh2/libssh2/blob/e5732992b1d2cf238dab636852aade4c52caff99/src/misc.c#L128-L187

In theory it seems like what we would have to do here is:

  1. Stop overriding the default Curl send/recv functions (in theory, if I'm understanding things correctly, that would mean we inherit the proper socket setup to handle the proxy connection).
  2. Use libssh2_session_callback_set to override the send/recv functions to call Curl_write / Curl_read.

I did try doing that with very limited success, so I'm probably missing something here.

bagder added a commit that referenced this issue Sep 28, 2020
Reported-by: Robin Douine
Fixes #4295
@bagder bagder closed this in edfb616 Sep 29, 2020
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@bagder @FBNeal @Koaxiel @shilpa-gupta and others
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