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Fork before entering shared-state command substitution

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The code contains various checks to see if a subshell needs to
fork, like this one in the ulimit builtin:

	if(shp->subshell && !shp->subshare)
		sh_subfork();

All checks of this form are fatally broken, as each one of them
causes shared-state command substitutions to ignore parent virtual
subshells.

Currently the only feasible way to fix this is to fork a virtual
subshell before executing a shared-state command substitution in
it. In the long term I think shared-state command substitutions
should probably be redesigned to disassociate them completely from
the virtual subshell mechanism.

src/cmd/ksh93/sh/macro.c: comsubst():
- If we're in a non-subshare virtual subshell, fork it before
  entering a type 2 (subshare) command substitution.

src/cmd/ksh93/sh/subshell.c:
- sh_assignok(): Remove subshare fix from 911d6b06 as it's
  redundant now that the parent of a subshare is never a virtual
  subshell. Go back to not doing anything if the current "subshell"
  is a subshare.
- sh_subtracktree(), sh_subfuntree(): Similarly, remove the
  now-redundant subshare fixes from 13c57e4b.

src/cmd/ksh93/sh/xec.c: sh_exec():
- Fix a separate bug: only fork a virtual subshell before running a
  background job if that "subshell" is not a subshare.

src/cmd/ksh93/tests/subshell.sh:
- Add test for bug fixed in xec.c.
- Add tests for 'ulimit', 'builtin' and 'exec' run in subshare
  within subshell -- all commands that use checks of the form
  'if(sh.subshell && !sh.subshare) sh_subfork();'.

Resolves: https://github.com/ksh93/ksh/issues/289
This commit is contained in:
Martijn Dekker 2021-05-01 00:47:39 +01:00
parent 72fe631b2f
commit 88a1f3d661
5 changed files with 29 additions and 38 deletions
Download patch file Download diff file Expand all files Collapse all files

41
src/cmd/ksh93/sh/subshell.c
View file

@ -273,32 +273,11 @@ Namval_t *sh_assignok(register Namval_t *np,int add)
Namarr_t *ap;
unsigned int save;
/*
* Don't create a scope if told not to (see nv_restore()).
* Don't create a scope if told not to (see nv_restore()) or if this is a subshare.
* Also, moving/copying ${.sh.level} (SH_LEVELNOD) may crash the shell.
*/
if(subshell_noscope || add<2 && np==SH_LEVELNOD)
if(subshell_noscope || sh.subshare || add<2 && np==SH_LEVELNOD)
return(np);
/*
* Don't create a scope for a ${ shared-state command substitution; } (a.k.a. subshare).
* However, if the subshare is in a virtual subshell, we need to create a scope in that.
* If so, temporarily make that the current subshell and call this function recursively.
*/
if(shp->subshare)
{
while(subshell_data->subshare) /* move up as long as parent is also a subshare */
subshell_data = subshell_data->prev;
subshell_data = subshell_data->prev; /* move to first non-subshare parent */
if(!subshell_data) /* if that's not a virtual subshell, don't create a scope */
{
subshell_data = sp;
return(np);
}
shp->subshare = 0;
np = sh_assignok(np,add);
shp->subshare = 1;
subshell_data = sp;
return(np);
}
if((ap=nv_arrayptr(np)) && (mp=nv_opensub(np)))
{
shp->last_root = ap->table;
@ -427,14 +406,8 @@ static void nv_restore(struct subshell *sp)
Dt_t *sh_subtracktree(int create)
{
register struct subshell *sp = subshell_data;
if(create && sh.subshell)
if(create && sh.subshell && !sh.subshare)
{
if(sh.subshare)
{
while(sp->subshare) /* move up as long as parent is also a ${ subshare; } */
sp = sp->prev;
sp = sp->prev; /* move to first non-subshare parent */
}
if(sp && !sp->strack)
{
sp->strack = dtopen(&_Nvdisc,Dtset);
@ -453,14 +426,8 @@ Dt_t *sh_subtracktree(int create)
Dt_t *sh_subfuntree(int create)
{
register struct subshell *sp = subshell_data;
if(create && sh.subshell)
if(create && sh.subshell && !sh.subshare)
{
if(sh.subshare)
{
while(sp->subshare) /* move up as long as parent is also a ${ subshare; } */
sp = sp->prev;
sp = sp->prev; /* move to first non-subshare parent */
}
if(sp && !sp->sfun)
{
sp->sfun = dtopen(&_Nvdisc,Dtoset);