Bug 616684

Summary: wrong redirections with SIGPIPE traps
Product: Red Hat Enterprise Linux 6 Reporter: Michal Hlavinka <mhlavink>
Component: kshAssignee: Michal Hlavinka <mhlavink>
Status: CLOSED ERRATA QA Contact: BaseOS QE - Apps <qe-baseos-apps>
Severity: medium Docs Contact:
Priority: medium    
Version: 6.1CC: kvolny, mfranc, ovasik, tsmetana
Target Milestone: rc   
Target Release: ---   
Hardware: All   
OS: Linux   
Whiteboard:
Fixed In Version: Doc Type: Bug Fix
Doc Text:
When a ksh script contained the "trap" command to capture a "SIGPIPE" signal, sending this signal via the built-in "echo" command could cause its output to be incorrectly added to the redirected output of an external command. With this update, ksh now flushes the output buffer before redirecting any output streams.
 Story Points: ---
Clone Of: 615284 Environment:
Last Closed: 2011-05-19 13:50:03 UTC Type: ---
Regression: --- Mount Type: ---
Documentation: --- CRM:
Verified Versions: Category: ---
oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: --- Target Upstream Version:
Embargoed:
Bug Depends On: 615284    
Bug Blocks:    
Attachments:
Description Flags
patch to fix this jskala: review+

Description Michal Hlavinka 2010-07-21 07:53:06 UTC 
+++ This bug was initially created as a clone of Bug #615284 +++

Description of problem:
In a ksh script, when SIGPIPE trap action is specified and SIGPIPE occurs by the output of the built-in echo command, the output appears in a redirect file of a external command.

Version-Release number of selected component (if applicable):
ksh-20100202-1.el5

How reproducible:
Always

Steps to Reproduce:

Run the following scripts with

ssh localhost /path/to/the/script.ksh >/dev/null

Steps to reproduce:

Case 1:
-------

the script.ksh is:

#!/bin/ksh
killparent()
{
	sleep 1
	/bin/kill -9 $1
}
trap "/bin/echo trap > /dev/null" 13
killparent ${PPID} &
/usr/bin/yes
print "echo1"
/bin/echo "echo2" > /tmp/echo2
trap 13

After running the script with ssh print the contents of the resulting file:
# cat /tmp/echo2

Actual results:
echo1
echo2

Expected results:
echo2

Case 2:
-------

the script.ksh is

#!/bin/ksh
killparent()
{
	sleep 1
	/bin/kill -9 $1
}
trap "/bin/echo trap >> /tmp/trap" 13
killparent ${PPID} &
/usr/bin/yes
echo "echo1"
/bin/echo "echo2"
trap 13

After running the script with ssh print the contents of the resulting file:
# cat /tmp/trap

Actual results:
echo1
trap
trap

Expected results:
trap
trap

Additional information:
Seems that the output of the echo builtin command is buffered and the buffer is flushed upon forking a child process.  However when the flush fails the content of the buffer is not erased and then appears in where it should not.

Maybe the ksh should either delete the buffer after flush (even unsucessful), not to buffer the echo output or not to buffer the redirection output.

--- Additional comment from mhlavink on 2010-07-21 03:49:56 EDT ---

patch attached in original bug
Comment 2 Michal Hlavinka 2011-01-05 13:18:53 UTC 
Created attachment 471856 [details]
patch to fix this
Comment 5 Martin Prpič 2011-03-16 15:53:45 UTC 
    Technical note added. If any revisions are required, please edit the "Technical Notes" field
    accordingly. All revisions will be proofread by the Engineering Content Services team.
    
    New Contents:
* When a ksh script contained the "trap" command to capture a "SIGPIPE" signal, sending this signal via the built-in "echo" command could cause its output to be incorrectly added to the redirected output of an external command. With this update, ksh now flushes the output buffer before redirecting any output streams.
Comment 6 Martin Prpič 2011-03-16 15:53:54 UTC 
    Technical note updated. If any revisions are required, please edit the "Technical Notes" field
    accordingly. All revisions will be proofread by the Engineering Content Services team.
    
    Diffed Contents:
@@ -1 +1 @@
-* When a ksh script contained the "trap" command to capture a "SIGPIPE" signal, sending this signal via the built-in "echo" command could cause its output to be incorrectly added to the redirected output of an external command. With this update, ksh now flushes the output buffer before redirecting any output streams.+When a ksh script contained the "trap" command to capture a "SIGPIPE" signal, sending this signal via the built-in "echo" command could cause its output to be incorrectly added to the redirected output of an external command. With this update, ksh now flushes the output buffer before redirecting any output streams.
Comment 7 errata-xmlrpc 2011-05-19 13:50:03 UTC 
An advisory has been issued which should help the problem
described in this bug report. This report is therefore being
closed with a resolution of ERRATA. For more information
on therefore solution and/or where to find the updated files,
please follow the link below. You may reopen this bug report
if the solution does not work for you.

http://rhn.redhat.com/errata/RHBA-2011-0645.html