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Fix subshell leak for 3 special variables (re: 417883df, bd3e2a80)

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Using a process of elimination I've identified ${.sh.level}
(SH_LEVELNOD) as the cause of the crash. This node apparently
cannot be copied or moved without destabilising the shell. It
contains the current depth of function calls and it cannot be
changed by assignment, so this is not actually a problem.
Meanwhile, this commit re-fixes it for the other three.

src/cmd/ksh93/sh/subshell.c:
- Simplify sh_assignok() by removing special-casing for L_ARGNOD,
  SH_SUBSCRNOD and SH_NAMENOD. 'add' now has 3 modes (0, 1, 2).
- The test for a ${ subshare; } was actually wrong. sp->subshare is
  a saved backup value. We must test shp->subshare. (re: a9de50bf)

src/cmd/ksh93/bltins/typeset.c:
- setall(): Update the mode 3 sh_assignok() call.

src/cmd/ksh93/tests/variables.sh:
- Regress-test subshell leaks for all special variables except
  ${.sh.level}.
This commit is contained in:
Martijn Dekker 2020-09-05 19:31:28 +02:00
parent 417883dfdd
commit e1c41bb2de
3 changed files with 23 additions and 8 deletions
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2
src/cmd/ksh93/bltins/typeset.c
View file

@ -800,7 +800,7 @@ static int setall(char **argv,register int flag,Dt_t *troot,struct tdata *tp
if (tp->aflag && (tp->argnum>0 || (curflag!=newflag)))
{
if(shp->subshell)
sh_assignok(np,3);
sh_assignok(np,2);
if(troot!=shp->var_tree)
nv_setattr(np,newflag&~NV_ASSIGN);
else

12
src/cmd/ksh93/sh/subshell.c
View file

@ -235,8 +235,6 @@ int nv_subsaved(register Namval_t *np)
* add == 1: Create a copy of the node pointer in the current virtual subshell.
* add == 2: This will create a copy of the node pointer like 1, but it will disable the
* optimization for ${.sh.level}.
* add == 3: This is like 1, but it will never skip the following variables:
* ${.sh.level}, $_, ${.sh.subscript} and ${.sh.name}.
*/
Namval_t *sh_assignok(register Namval_t *np,int add)
{
@ -248,11 +246,11 @@ Namval_t *sh_assignok(register Namval_t *np,int add)
Namval_t *mpnext;
Namarr_t *ap;
unsigned int save;
/* don't bother to save if in a ${ subshare; } */
if(sp->subshare)
return(np);
/* don't bother with this */
if(!sp->shpwd || (add != 3 && ((add != 2 && np==SH_LEVELNOD) || np==L_ARGNOD || np==SH_SUBSCRNOD || np==SH_NAMENOD)))
/*
* Don't save if told not to (see nv_restore()) or if we're in a ${ subshare; }.
* Also, moving/copying ${.sh.level} (SH_LEVELNOD) may crash the shell.
*/
if(!sp->shpwd || shp->subshare || add<2 && np==SH_LEVELNOD)
return(np);
if((ap=nv_arrayptr(np)) && (mp=nv_opensub(np)))
{

17
src/cmd/ksh93/tests/variables.sh
View file

@ -1011,6 +1011,23 @@ $SHELL -c '
e=$?
((e == 1)) || err_exit "Failure in making one or more special variables readonly in a subshell (exit status $e)"
# ... subshell leak test
$SHELL -c '
errors=0
for var
do if [[ $var == .sh.level ]]
then continue # known to fail
fi
if eval "($var=bug); [[ \${$var} == bug ]]" 2>/dev/null
then echo " $0: special variable $var leaks out of subshell" >&2
let errors++
fi
done
exit $((errors + 1))
' subshell_leak_test "$@"
e=$?
((e == 1)) || err_exit "One or more special variables leak out of a subshell (exit status $e)"
# ======
# ${.sh.pid} should be the forked subshell's PID
(