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From 27909acb584aed231d757d1d63c6c62b57c8e152 Mon Sep 17 00:00:00 2001
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From: Vincent Mihalkovic <vmihalko@redhat.com>
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Date: Mon, 3 Jan 2022 14:03:20 +0100
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Subject: [PATCH] Fix race conditions running external commands with job
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control on
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When ksh is compiled with SHOPT_SPAWN (the default), which uses
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posix_spawn(3) or vfork(2) (via sh_ntfork()) to launch external
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commands, at least two race conditions occur when launching
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external commands while job control is active. See:
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https://bugs.launchpad.net/ubuntu/+source/ksh/+bug/1887863/comments/3
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https://www.mail-archive.com/ast-developers@research.att.com/msg00717.html
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The basic issue is that this performance optimisation is
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incompatible with job control, because it uses a spawning mechanism
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that doesn't copy the parent process' memory pages into the child
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process, therefore no state that involves memory can be set before
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exec-ing the external program. This makes it impossible to
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correctly set the terminal's process group ID in the child process,
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something that is essential for job control to work.
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src/cmd/ksh93/sh/xec.c:
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- Use sh_fork() instead of sh_ntfork() if job control is active.
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This uses fork(2), which is 30%-ish slower on most sytems, but
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allows for correctly setting the terminal process group.
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Fixes: https://github.com/ksh93/ksh/issues/79
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---
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src/cmd/ksh93/sh/xec.c | 2 +-
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1 file changed, 1 insertion(+), 1 deletion(-)
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diff --git a/src/cmd/ksh93/sh/xec.c b/src/cmd/ksh93/sh/xec.c
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index ae13178..be57a6b 100644
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--- a/src/cmd/ksh93/sh/xec.c
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+++ b/src/cmd/ksh93/sh/xec.c
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@@ -1737,7 +1737,7 @@ int sh_exec(register const Shnode_t *t, int flags)
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#else
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#if SHOPT_SPAWN
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# ifdef _lib_fork
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- if(com)
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+ if(com && !job.jobcontrol)
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parent = sh_ntfork(shp,t,com,&jobid,ntflag);
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else
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parent = sh_fork(shp,type,&jobid);
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--
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2.31.1
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