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Implement a better fix for unsetting special env vars

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The regression this commit fixes was first introduced in ksh93t
2008-07-25. It was previously worked around in 6f0e008c by forking
subshells if any special environment variable is unset.

The reason why this problem doesn't occur in ksh93s+ is because in
that version of ksh sh_assignok never moves nodes, it only clones
them. The second argument doesn't set NV_MOVE, which makes
`sh_assignok(np,0)` is similar to `sh_assignok(np,1)`. In ksh93t and
higher, setting the second argument to zero causes the node to be moved
with NV_MOVE, which causes the discipline function associated with
the variable node to be removed when `np->nvfun` is set to zero (i.e.
NULL). This is why a command like `(unset LC_NUMERIC; LC_NUMERIC=invalid)`
doesn't print a diagnostic, as it looses its discipline function.

This patch fixes the problem by cloning the node with sh_assignok
if it is a special variable with a discipline function. This allows
special variables to work as expected in virtual subshells. The
original workaround has been kept for the $PATH variable only, as
hash tables are still broken in virtual subshells. It has been updated
accordingly to only fork subshells if it detects the variable node
for PATH. I have added two more regression tests for changing the
PATH in subshells to make sure hash tables continue working as
expected with this fix.

src/cmd/ksh93/bltins/typeset.c:
 - Only fork virtual subshells if the PATH will be changed. If a
   variable is a special variable with a discipline function, it
   should be just be cloned, not moved.

src/cmd/ksh93/sh/nvdisc.c:
 - Add a comment to clarify that NV_MOVE will delete the discipline
   function associated with the node.

src/cmd/ksh93/tests/subshells.sh:
 - Add two more regression tests for unsetting the PATH in subshells,
   one for if PATH is being pointed to by a nameref. Condense the
   hash table tests by moving the main test into a single function.
This commit is contained in:
Johnothan King 2020-06-13 05:12:10 -07:00
parent 289f56cd4c
commit 7b994b6a7e
3 changed files with 29 additions and 14 deletions
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23
src/cmd/ksh93/bltins/typeset.c
View file

@ -1208,11 +1208,9 @@ static int unall(int argc, char **argv, register Dt_t *troot, Shell_t* shp)
}
/*
* Check for variables with internal trap/discipline functions (PATH, LANG, LC_*, LINENO, etc.).
* Unsetting these in a virtual/non-forked subshell would cause them to lose their discipline actions,
* so, for example, (unset PATH; PATH=/dev/null; ls) would run 'ls'! Until a fix is found, make the problem
* go away by forking the subshell. To avoid crashing, this must be done before calling sh_pushcontext(),
* so we need to loop through the args separately to check if any variable to unset has a discipline function.
* Unsetting the PATH in a non-forked subshell will cause the parent shell's hash table to be reset,
* so fork to work around the problem. To avoid crashing, this must be done before calling sh_pushcontext(),
* so we need to loop through the args separately and check if any node is equal to PATHNOD.
*/
if(shp->subshell && !shp->subshare && troot==shp->var_tree)
{
@ -1222,8 +1220,8 @@ static int unall(int argc, char **argv, register Dt_t *troot, Shell_t* shp)
np=nv_open(name,troot,NV_NOADD|nflag);
if(!np)
continue;
/* Has discipline function, and is not a nameref? */
if(np->nvfun && np->nvfun->disc && !nv_isref(np))
/* Are we changing the PATH? */
if(np==PATHNOD)
{
nv_close(np);
sh_subfork();
@ -1276,8 +1274,19 @@ static int unall(int argc, char **argv, register Dt_t *troot, Shell_t* shp)
}
if(shp->subshell)
{
if(!nv_isattr(np,NV_NODISC|NV_ARRAY) && !nv_isvtree(np))
{
/*
* Variables with internal trap/discipline functions (LC_*, LINENO, etc.) need to be
* cloned, as moving them will remove the discipline function.
*/
np=sh_assignok(np,1);
}
else
np=sh_assignok(np,0);
}
}
if(!nv_isnull(np) || nv_size(np) || nv_isattr(np,~(NV_MINIMAL|NV_NOFREE)))
_nv_unset(np,0);

2
src/cmd/ksh93/sh/nvdisc.c
View file

@ -962,7 +962,7 @@ int nv_clone(Namval_t *np, Namval_t *mp, int flags)
{
if(nv_isattr(np,NV_INTEGER))
mp->nvalue.ip = np->nvalue.ip;
np->nvfun = 0;
np->nvfun = 0; /* This will remove the discipline function, if there is one */
np->nvalue.cp = 0;
if(!nv_isattr(np,NV_MINIMAL) || nv_isattr(mp,NV_EXPORT))
{

16
src/cmd/ksh93/tests/subshell.sh
View file

@ -710,13 +710,19 @@ v=${ eval 'al'; alias al='echo subshare'; } && [[ $v == 'mainalias' && $(eval 'a
|| err_exit 'alias redefinition fails to survive ${ ...; }'
# Resetting a subshell's hash table should not affect the parent shell
(hash -r)
[[ $(hash) ]] || err_exit $'resetting the hash table in a subshell affects the parent shell\'s hash table'
(PATH="$PATH")
[[ $(hash) ]] || err_exit $'resetting the PATH in a subshell affects the parent shell\'s hash table'
check_hash_table()
{
[[ $(hash) ]] || err_exit $'resetting the hash table in a subshell affects the parent shell\'s hash table'
# Ensure the hash table isn't empty before the next test is run
hash -r chmod
}
(hash -r); check_hash_table
(PATH="$PATH"); check_hash_table
(unset PATH); check_hash_table
(nameref PATH_TWO=PATH; unset PATH_TWO); check_hash_table
# Adding a utility to a subshell's hash table should not affect the parent shell
hash -r chmod
(hash cat)
[[ $(hash) == "chmod=$(whence -p chmod)" ]] || err_exit $'changes to a subshell\'s hash table affect the parent shell'