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Error out on 'redirect >foo' inside ${ shared-state comsub; }

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The following caused an infinite loop:

        v=${ exec >/dev/tty; }
        v=${ redirect >/dev/tty; }

Even the original authors didn't figure out how to 'exec >foo' or
'redirect >foo' inside a non-forking command substitution, so they
fork it by calling sh_subfork(). If we delete that call, even
normal command substitutions enter into that infinite loop. But of
course a shared-state comsub can never fork as it would no longer
share its state. Without a solution to make this work without
forking, an error message is the only sensible thing left to do.

src/cmd/ksh93/sh/io.c: sh_redirect():
- If we're redirecting standard output (1), the redirection is
  permanent as in 'exec'/'redirect' (flag==2), and we're in a
  subshare, then error out.

Resolves: https://github.com/ksh93/ksh/issues/128
This commit is contained in:
Martijn Dekker 2021-02-20 19:52:08 +00:00
parent e1690f61ff
commit 500757d78b
1 changed files with 7 additions and 2 deletions
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9
src/cmd/ksh93/sh/io.c
View file

@ -1126,8 +1126,13 @@ int sh_redirect(Shell_t *shp,struct ionod *iop, int flag)
{
iof=iop->iofile;
fn = (iof&IOUFD);
if(fn==1 && shp->subshell && !shp->subshare && (flag==2 || isstring))
sh_subfork();
if(fn==1)
{
if(shp->subshare && flag==2)
errormsg(SH_DICT,ERROR_exit(1),"cannot redirect stdout inside shared-state comsub");
if(shp->subshell && (flag==2 || isstring))
sh_subfork();
}
if(shp->redir0 && fn==0 && !(iof&IOMOV))
shp->redir0 = 2;
io_op[0] = '0'+(iof&IOUFD);