[SSHD-1144] type=SSH_FXP_CLOSE processing interrupted

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Abandoned
• Labels: user-confirmation-required user-response-required
• Assignee: Unassigned
• Reporter: Ivan Fiorentini
• Created: 16/Mar/21 09:19
• Updated: 20/Nov/21 06:56
• Resolved: 20/Nov/21 06:56

Description

Some sftp clients (e.g. lftp) after a file-get they disconnect from the server without wait for the close-file (type=SSH_FXP_CLOSE processing) response.
Here is an example of the "lftp get" exchange flow:

---- Running connect program (ssh -a -x -s -l user -p 22022 localhost sftp)
---> sending a packet, length=5, type=1(INIT), id=0
<--- SPENG SFTP Server - Primeur 
user@localhost's password: XXXX
<--- got a packet, length=576, type=2(VERSION), id=0
---- protocol version set to 6
---> sending a packet, length=10, type=16(REALPATH), id=1
<--- got a packet, length=33, type=104(NAME), id=1
---- home set to /IVNQM1/LOCALE
---- path on wire is `/IVNQM1/LOCALE/index.html'
---> sending a packet, length=47, type=3(OPEN), id=2
<--- got a packet, length=41, type=102(HANDLE), id=2
---- got file handle 6636636436393765363835616664643564333437396263386434386632303932 (32)
---> sending a packet, length=45, type=8(FSTAT), id=3
<--- got a packet, length=64, type=105(ATTRS), id=3
---- file info: size=612, date=Mon Mar 15 10:50:08 2021
---> sending a packet, length=53, type=5(READ), id=4
---> sending a packet, length=53, type=5(READ), id=5
<--- got a packet, length=621, type=103(DATA), id=4
---- data packet: pos=0, size=612
---> sending a packet, length=53, type=5(READ), id=6
<--- got a packet, length=28, type=101(STATUS), id=5
---- status code=1(EOF), message=End of file
---- eof
---> sending a packet, length=41, type=4(CLOSE), id=7
---- Disconnecting

On the server side, using apache sshd 2.6.0, the close-file processing (type=SSH_FXP_CLOSE processing) is delegated to the service thread "sshd-SftpSubsystem-thread-x" but when the disconnect (SSH_MSG_DISCONNECT) is received a "Thread.interrupt()" is invoked on the service thread "sshd-SftpSubsystem-thread-x".

The service thread "sshd-SftpSubsystem-thread-x" then could be interrupted at an unpredictable moment and this could cause a missed close of the file or leaving the close-file processing in an inconsistent state (for example some other resources not properly closed due to the "InterruptedException", etc.).

It seems there is  no way to avoid the interrupt of the service thread "sshd-SftpSubsystem-thread-x" and/or wait the termination of the "type=SSH_FXP_CLOSE processing".