Bug 1217236

Summary: ksh misbehavior if login shell "( cmd & )" does nothing and no error reported
Product: Red Hat Enterprise Linux 6 Reporter: Paulo Andrade <pandrade>
Component: kshAssignee: Michal Hlavinka <mhlavink>
Status: CLOSED ERRATA QA Contact: Martin Kyral <mkyral>
Severity: medium Docs Contact: Milan Navratil <mnavrati>
Priority: medium    
Version: 6.6CC: dkutalek, mnavrati, ovasik
Target Milestone: rcKeywords: Patch
Target Release: ---   
Hardware: All   
OS: All   
Whiteboard:
Fixed In Version: ksh-20120801-32.el6 Doc Type: Bug Fix
Doc Text:
KornShell no longer omits a background process in a command list when forking Due to a bug in KornShell (ksh), forking a background process in a command list could previously omit that process completely. The source code that handles forking sub-processes has been modified, and a background process in a command list is now executed as expected.
Story Points: ---
Clone Of:
: 1217237 1217238 (view as bug list) Environment:
Last Closed: 2016-05-11 00:45:47 UTC Type: Bug
Regression: --- Mount Type: ---
Documentation: --- CRM:
Verified Versions: Category: ---
oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: --- Target Upstream Version:
Bug Depends On:    
Bug Blocks: 1075802, 1172231, 1217237, 1217238, 1254457, 1269889    

Description Paulo Andrade 2015-04-29 20:28:56 UTC
To test, either have ksh as login shell, or create a test user.
Then ssh localhost.

Sample session:

---8<---
$ cd /tmp/alan
$ cat tst.ksh
#!/bin/ksh

D=$(date)
echo $D > /tmp/alan/tst.dat

$ ls
tst.ksh
$ (ksh /tmp/alan/tst.ksh &)
[1]	28190
$ ls
tst.ksh
---8<---

This happens due to a double fork, once for "( cmd )" and
then the first fork forks again due to the "&", but, just
when the child branches, it receives a SIGHUP and
immediately exits.

I tested a quick&dirty patch, that basically reverts to
rhel5 ksh behavior, and there are no regressions in the
test cases.

---8<---
diff -up ksh-20120801/src/cmd/ksh93/sh/xec.c.orig ksh-20120801/src/cmd/ksh93/sh/xec.c
--- ksh-20120801/src/cmd/ksh93/sh/xec.c.orig	2015-04-28 16:55:25.521818636 -0300
+++ ksh-20120801/src/cmd/ksh93/sh/xec.c	2015-04-28 16:56:34.037753565 -0300
@@ -2059,16 +2059,20 @@ int sh_exec(register const Shnode_t *t,
 			}
 			else if(((type=t->par.partre->tre.tretyp)&FAMP) && ((type&COMMSK)==TFORK))
 			{
+#if 0
 				pid_t	pid;
 				sfsync(NIL(Sfio_t*));
 				while((pid=fork())< 0)
 					_sh_fork(shp,pid,0,0);
 				if(pid==0)
 				{
+#endif
 					sh_exec(t->par.partre,flags);
+#if 0
 					shp->st.trapcom[0]=0;
 					sh_done(shp,0);
 				}
+#endif
 			}
 			else
 				sh_subshell(shp,t->par.partre,flags,0);
---8<---

I also asked upstream, see http://lists.research.att.com/pipermail/ast-users/2015q2/004754.html
but actually, there is a bad comment there, about crashes if
running it as "( cmd ) &". Likely it was due to the way I was
debugging it.

Note that if one has bash as login shell, then starts, or exec
ksh, or even if has ksh as login shell, and first exec ksh,
it will work, because then SIGHUP will be blocked in the
"orphan" process (orphan due to double fork).

Comment 9 errata-xmlrpc 2016-05-11 00:45:47 UTC
Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory, and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

https://rhn.redhat.com/errata/RHBA-2016-0932.html