SFTP transfer broken if buffer > 100Kb

[pwo]

"OpenSSH for Windows" version
7.7.2.2

Server OperatingSystem
Windows Server 2019 Standard

Client OperatingSystem
CentOS Linux release 7.6.1810 (Core)
OpenSSH_7.4p1, OpenSSL 1.0.2k-fips 26 Jan 2017

What is failing
Using a sftp buffer greater than 102400 fails to transfer large files.
$ ls -l fil
-rw-r--r--. 1 root root 1048576 May 31 16:52 fil
$ sftp -B 102401 sshtest@windows-server
sshtest@windows-server's password:
Connected to windows-server.
sftp> put fil
Uploading fil to /fil
fil 9% 100KB 8.8MB/s 00:00 ETA
Couldn't write to remote file "/fil": Failure
sftp>

This is related to the 100Kb read/write buffers in fileio.c

This can not be triggered from a Windows sftp.exe client because the read buffer is also capped to 102400 bytes.

Expected output
File uploaded successfully.

Actual output
3716 2019-05-31 16:55:30.395 session opened for local user sshtest from [a.b.c.d]
3716 2019-05-31 16:55:30.395 received client version 3
3716 2019-05-31 16:55:30.395 debug3: request 1: realpath
3716 2019-05-31 16:55:30.395 realpath "."
3716 2019-05-31 16:55:30.395 debug1: request 1: sent names count 1
3716 2019-05-31 16:55:31.656 debug3: request 2: open flags 26
3716 2019-05-31 16:55:31.656 open "/fil" flags WRITE,CREATE,TRUNCATE mode 0644
3716 2019-05-31 16:55:31.656 debug1: request 2: sent handle handle 0
3716 2019-05-31 16:55:31.671 debug1: request 3: write "/fil" (handle 0) off 0 len 102401
3716 2019-05-31 16:55:31.671 debug2: nothing at all written
3716 2019-05-31 16:55:31.671 debug3: request 3: sent status 4
3716 2019-05-31 16:55:31.671 sent status Failure
3716 2019-05-31 16:55:31.671 debug3: request 3: close handle 0
3716 2019-05-31 16:55:31.671 close "/fil" bytes read 0 written 0
3716 2019-05-31 16:55:31.671 debug3: request 3: sent status 0
3716 2019-05-31 16:55:31.671 sent status Success
3716 2019-05-31 16:55:39.810 debug1: read eof
3716 2019-05-31 16:55:39.810 session closed for local user sshtest from [a.b.c.d]

[ronl]

Any estimate when this may be fixed?

[niallmcconnell]

Has there been any progress on this issue? Thanks

[vthiebaut10]

@pwo Please try these private binaries and let us knows if it fixes your issue.
Please follow these steps:

1. stop the sshd service (net stop sshd)
2. cd to openssh bin folder.
3. take backup of sftp-server.exe and sshd.exe
4. download and copy the private sftp-server.exe and sshd.exe to bin folder.
5. start sshd service (net start sshd)
6. start sftp connection and try your scenario

Let us knows if that solves your issue

[niallmcconnell]

Hi guys,
We have downloaded and tested the new exe files and they have worked as expected. We are now able to transfer binary files of any size to the remote OpenSSH installation. Thanks for the fix.
Niall