[Bug 3177] New: sshd process had became <defunct> and could not accept requests any more after many count sftp accesses.

[bugzilla-daemon at mindrot.org]

https://bugzilla.mindrot.org/show_bug.cgi?id=3177

            Bug ID: 3177
           Summary: sshd process had became <defunct> and could not accept
                    requests any more after many count sftp accesses.
           Product: Portable OpenSSH
           Version: 8.2p1
          Hardware: amd64
                OS: Linux
            Status: NEW
          Severity: critical
          Priority: P5
         Component: sshd
          Assignee: unassigned-bugs at mindrot.org
          Reporter: zhlonggang at aliyun.com

Created attachment 3405
  --> https://bugzilla.mindrot.org/attachment.cgi?id=3405&action=edit
sshd log which has a DEBUG3 log level

I has a sftp file server in our production environment, which is
centos6.8 os with openssh-5.3p1.

Because openssh-5.3p1 is too old.Recently I want to upgrade
openssh-5.3p1 with a newest openssh-8.2p1. After a downloading,
compiling, deployment, and a few ssh/sftp command-line tests,
everything is ok. The newest openssh-8.2p1 seems work normally as
expected. But when I tested with a java client program which calls
Jch-5.4 sdk to upload a file to the openssh-8.2p1 sftp file server in a
loop, my problem occured. After many successful sftp accesses and a few
hours later, the java client program accessed the sftp server failed
with the following exception:"Session.connect:
java.net.SocketTimeoutException: Read timed out". When I used a sftp or
ssh command to access the server, the command was blocked for a long
time and could not return any more, but I could telnet the port
successfully. 

When I logined into the sftp file server, ps the process, I found the
following infomaion:

root     11742     1  0 6月03 ?       00:00:02 sshd:
/usr/local/openssh-8.2p1/sbin/sshd -p 99 -f
/etc/ssh/sshd_config_sftp.bad [listener] 0 of 10-100 startups
root     11775 11742  0 6月03 ?       00:00:00 sshd: testuser1 [priv]
testuse+ 11777 11775  0 6月03 ?       00:00:13 sshd: testuser1 at notty
root     15110   923  0 18:06 ?        00:00:00 sshd: root at pts/0
root     15128 15112  0 18:06 pts/0    00:00:00 grep --color=auto sshd
root     21936 11742  0 6月03 ?       00:00:00 [sshd] <defunct>

I could see a sshd process which had become into a defunct process. It
is the problem.

I have ran the java client program for many times, But I got the same
result, and I counld not found any error info in the sshd log.

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