[Bug 916] SFTP over SSH died after roughly 20MB when asking for >64k chunks

[bugzilla-daemon at mindrot.org]

http://bugzilla.mindrot.org/show_bug.cgi?id=916

           Summary: SFTP over SSH died after roughly 20MB when asking for
                    >64k chunks
           Product: Portable OpenSSH
           Version: 3.8.1p1
          Platform: ix86
        OS/Version: Linux
            Status: NEW
          Severity: normal
          Priority: P2
         Component: sshd
        AssignedTo: openssh-bugs at mindrot.org
        ReportedBy: z3p at twistedmatrix.com


I have a SSHv2/SFTPv3 implementation written in Python.  I have been trying to
use a chunk size for SFTP downloading of 128k against the 3.8.1p1
sshd/sftp-server.  I only get 64k back, which is because of the hardcoded buffer
in sftp-server.c, but that's not the problem.  After roughly 20MB of 64kb chunks
(asking for 128kb) the server hangs and stops sending data.
Interestingly, talking directly to sftp-server does not demonstrate this bug,
which leads me to believe that the bug is somewhere in sshd, although I have no
idea how that could be.  I'm using a local window size and local maximum packet
size that is large enough for 128k packets.
I'll attach a Python script that demonstrates the bug.



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