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Fix corner-case >&- redirection leak out of subshell

Browse source 
Reproducer:

    exec 9>&1
    ( { exec 9>&1; } 9>&- )
    echo "test" >&9 # => 9: cannot open [Bad file descriptor]

The 9>&- incorrectly persists beyond the { } block that it
was attached to *and* beyond the ( ) subshell. This is yet another
bug with non-forking subshells; forking it with something like
'ulimit -t unlimited' works around the bug.

In over a year we have not been able to find a real fix, but I came
up with a workaround that forks a virtual subshell whenever it
executes a code block with a >&- or <&- redirection attached. That
use case is obscure enough that it should not cause any performance
regression except in very rare corner cases.

src/cmd/ksh93/sh/xec.c: sh_exec(): TSETIO:
- This is where redirections attached to code blocks are handled.
  Check for a >&- or <&- redirection using bit flaggery from
  shnodes.h and fork if we're executing such in a virtual subshell.

Resolves: https://github.com/ksh93/ksh/issues/161
Thanks to @ko1nksm for the bug report.
This commit is contained in:
Martijn Dekker 2022-02-11 02:21:47 +00:00
parent 14a43a0a88
commit 6304dfce41
4 changed files with 53 additions and 2 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

5
NEWS
View file

@ -3,6 +3,11 @@ For full details, see the git log at: https://github.com/ksh93/ksh/tree/1.0
Any uppercase BUG_* names are modernish shell bug IDs.
2022-02-11:
- Fixed a bug in which a >&- or <&- redirection could persist past a
subshell in certain corner cases involving 'exec' or 'redirect'.
2022-02-08:
- Multiple bugs were fixed in the method that ksh uses to execute a shell

2
src/cmd/ksh93/include/version.h
View file

@ -21,7 +21,7 @@
#define SH_RELEASE_FORK "93u+m" /* only change if you develop a new ksh93 fork */
#define SH_RELEASE_SVER "1.0.0-beta.2" /* semantic version number: https://semver.org */
#define SH_RELEASE_DATE "2022-02-08" /* must be in this format for $((.sh.version)) */
#define SH_RELEASE_DATE "2022-02-11" /* must be in this format for $((.sh.version)) */
#define SH_RELEASE_CPYR "(c) 2020-2022 Contributors to ksh " SH_RELEASE_FORK
/* Scripts sometimes field-split ${.sh.version}, so don't change amount of whitespace. */

16
src/cmd/ksh93/sh/xec.c
View file

@ -1821,6 +1821,22 @@ int sh_exec(register const Shnode_t *t, int flags)
int jmpval, waitall = 0;
int simple = (t->fork.forktre->tre.tretyp&COMMSK)==TCOM;
struct checkpt *buffp = (struct checkpt*)stkalloc(sh.stk,sizeof(struct checkpt));
if(sh.subshell && !sh.subshare && t->fork.forkio)
{
/* Subshell forking workaround for https://github.com/ksh93/ksh/issues/161
* Check each redirection for >&- or <&-
* TODO: find the elusive real fix */
struct ionod *i = t->fork.forkio;
do
{
if((i->iofile & ~(IOUFD|IOPUT)) == (IOMOV|IORAW) && !strcmp(i->ioname,"-"))
{
sh_subfork();
break;
}
}
while(i = i->ionxt);
}
sh_pushcontext(buffp,SH_JMPIO);
if(type&FPIN)
{

32
src/cmd/ksh93/tests/io.sh
View file

@ -766,7 +766,7 @@ got=$(export tmp; "$SHELL" -ec \
# ======
# Redirections of the form {varname}>file stopped working if brace expansion was turned off
((SHOPT_BRACEPAT)) && set +B
{ redirect {v}>$tmp/v.out && echo ok >&$v; } 2>/dev/null && redirect {v}>&-
(redirect {v}>$tmp/v.out && echo ok >&$v && redirect {v}>&-) 2>/dev/null
((SHOPT_BRACEPAT)) && set -B
[[ -r $tmp/v.out && $(<$tmp/v.out) == ok ]] || err_exit '{varname}>file not working with brace expansion turned off'
@ -924,5 +924,35 @@ then kill "$!" # the sleep process
else err_exit "comsub hangs after fork with stdout redirection"
fi
# ======
# https://github.com/ksh93/ksh/issues/161
got=$(
set +x
redirect 2>&1 9>&1
( { redirect 9>&1; } 6<&2 9<&- )
echo "test" >&9 # => 9: cannot open [Bad file descriptor]
)
[[ $got == 'test' ]] || err_exit "File descriptor is unexpectedly closed after exec in subshell" \
"(expected 'test', got $(printf %q "$got"))"
got=$(
set +x
exec 2>&1 9>&1
exec 9>&-
v=$( { exec 9>&1; } )
echo "test" >&9
)
exp=': 9: cannot open ['
[[ $got == *"$exp"* ]] || err_exit "issue 161 hypothetical bug 1" \
"(expected match of *$(printf %q "$exp")*, got $(printf %q "$got"))"
got=$(
set +x
exec 2>&1
openfd() { exec 6>&1; }
openfd
echo "test" >&6
)
[[ $got == 'test' ]] || err_exit "issue 161 hypothetical bug 2" \
"(expected 'test', got $(printf %q "$got"))"
# ======
exit $((Errors<125?Errors:125))