Bug 60610

Summary: ssh returns wrong exit code
Product: [Retired] Red Hat Linux Reporter: Mike Bird <mgb>
Component: opensshAssignee: Nalin Dahyabhai <nalin>
Status: CLOSED ERRATA QA Contact: Brian Brock <bbrock>
Severity: medium Docs Contact:
Priority: medium    
Version: 7.2   
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Hardware: i386   
OS: Linux   
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Fixed In Version: Doc Type: Bug Fix
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Last Closed: 2002-03-03 07:14:00 UTC Type: ---
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oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
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Description Mike Bird 2002-03-02 10:36:44 UTC 
Description of Problem: After upgrading from kernel-2.4.9-21 to kernel-2.4.9-31,
ssh returns wrong exit code under some circumstances (seriously munging our
systems management!)


Version-Release number of selected component (if applicable): 2.9p2-12


How Reproducible:

"ssh localhost rpm -qa </dev/null; echo $?"
should reveal exit code 0 but on most upgraded systems gives exit code 255

removing "ssh localhost" gives exit code 0 which is correct

adding "strace" before either "ssh" or "rpm" appears to show that the ssh/sshd
system is changing the 0 to -1.  However "ssh localhost exit 0" works correctly.
Comment 1 Mike Bird 2002-03-03 07:13:55 UTC 
The problem is a race in sshd which was exposed by small changes in the kernel. 
Here's a simpler test case:

ssh localhost perl -e
"'close(STDIN);close(STDOUT);close(STDERR);sleep(1);exit(0);'"

Because the fd's are closed before the process exits, the cleanup code in
session.c is used instead of the cleanup code in serverloop.c.  The session.c
cleanup code ignores the process exit code, contrary to spec which says that
sshd waits for process exit AND all fd's closed, then passes the exit code to
ssh.

The effect of the current code is to wait for process exit OR all fd's closed,
which results in the observed race as well as other incorrect behavior.

WORKAROUND

Until this is fixed, the following workaround seems to work in most cases. 
Instead of:

  ssh localhost foo

- use this:

  ssh localhost 'foo; exit $?'
Comment 2 Mike Bird 2002-03-09 01:43:50 UTC 
Bug does not exist in openssh-3.1p1-2 which was released today to fix a serious security bug.