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[perl #20613] Perl_magic_setsig/clearsig problems (patch included)
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From:
Anders Johnson
Date:
January 29, 2003 19:44
Subject:
[perl #20613] Perl_magic_setsig/clearsig problems (patch included)
Message ID:
rt-20613-49896.11.6328062813677@bugs6.perl.org
# New Ticket Created by "Anders Johnson"
# Please include the string: [perl #20613]
# in the subject line of all future correspondence about this issue.
# <URL: http://rt.perl.org/rt2/Ticket/Display.html?id=20613 >
I discovered a few problems with setting and clearing %SIG entries in
the Perl 5.8.0 production release (currently the same as the development
release). To wit:
+ Deleting a %SIG entry does not restore the default signal/hook
disposition.
+ The previous disposition SV refcount is decremented (possibly
resulting in its deallocation) *before* the new disposition is in place,
and while the handler is in an inconsistent state. If it's a coderef
with closures, then just about anything can happen at that point, which
is bad because DESTROY might need the new handler to be in place.
+ A signal can arrive while it's being dispositioned, which could, for
example, cause the program to terminate immediately while we're
switching from one handler to another.
+ There are a couple of apparently redundant "*svp=0" statements. (I
commented them, but I was too chicken to remove them.)
The patch includes a test case for the first 2 items. Here are a couple
of items that I might have screwed up and should be reviewed by a more
experienced Perl hacker:
+ The test case uses "$? & 0xFF" to see if the closed pipe exited from a
signal. Is this portable?
+ Is there any way (e.g. exception?) that Perl_magic_setsig() might
escape without restoring the sigprocmask? (If so, we could maybe use the
trick from POSIX::sigaction to get around that.) This could also result
in a memory leak (because "to_dec" would get ignored).
Here is the patch:
diff -Naur perl-5.8.0/mg.c perl-5.8.0-sig2/mg.c
--- perl-5.8.0/mg.c Sat Jun 15 13:16:44 2002
+++ perl-5.8.0-sig2/mg.c Wed Jan 29 13:27:34 2003
@@ -1061,19 +1061,48 @@
int
Perl_magic_clearsig(pTHX_ SV *sv, MAGIC *mg)
{
- I32 i;
+ /* XXX Some of this code was copied from Perl_magic_setsig. A
little
+ * refactoring might be in order.
+ */
+ register char *s;
STRLEN n_a;
- /* Are we clearing a signal entry? */
- i = whichsig(MgPV(mg,n_a));
- if (i) {
- if(PL_psig_ptr[i]) {
- SvREFCNT_dec(PL_psig_ptr[i]);
- PL_psig_ptr[i]=0;
- }
- if(PL_psig_name[i]) {
- SvREFCNT_dec(PL_psig_name[i]);
- PL_psig_name[i]=0;
- }
+ SV* to_dec;
+ s = MgPV(mg,n_a);
+ if (*s == '_') {
+ SV** svp;
+ if (strEQ(s,"__DIE__"))
+ svp = &PL_diehook;
+ else if (strEQ(s,"__WARN__"))
+ svp = &PL_warnhook;
+ else
+ Perl_croak(aTHX_ "No such hook: %s", s);
+ if (*svp) {
+ to_dec = *svp;
+ *svp = 0;
+ SvREFCNT_dec(to_dec);
+ }
+ }
+ else {
+ I32 i;
+ /* Are we clearing a signal entry? */
+ i = whichsig(s);
+ if (i) {
+#ifdef FAKE_DEFAULT_SIGNAL_HANDLERS
+ sig_defaulting[i] = 1;
+ (void)rsignal(i, &Perl_csighandler);
+#else
+ (void)rsignal(i, SIG_DFL);
+#endif
+ if(PL_psig_name[i]) {
+ SvREFCNT_dec(PL_psig_name[i]);
+ PL_psig_name[i]=0;
+ }
+ if(PL_psig_ptr[i]) {
+ to_dec=PL_psig_ptr[i];
+ PL_psig_ptr[i]=0;
+ SvREFCNT_dec(to_dec);
+ }
+ }
}
return 0;
}
@@ -1156,7 +1185,15 @@
register char *s;
I32 i;
SV** svp = 0;
+ /* Need to be careful with SvREFCNT_dec(), because that can have
side
+ * effects (due to closures). We must make sure that the new
disposition
+ * is in place before it is called.
+ */
+ SV* to_dec = 0;
STRLEN len;
+#ifdef HAS_SIGPROCMASK
+ sigset_t set, save;
+#endif
s = MgPV(mg,len);
if (*s == '_') {
@@ -1168,7 +1205,7 @@
Perl_croak(aTHX_ "No such hook: %s", s);
i = 0;
if (*svp) {
- SvREFCNT_dec(*svp);
+ to_dec = *svp;
*svp = 0;
}
}
@@ -1179,6 +1216,12 @@
Perl_warner(aTHX_ packWARN(WARN_SIGNAL), "No
such signal: SIG%s", s);
return 0;
}
+#ifdef HAS_SIGPROCMASK
+ /* Avoid having the signal arrive at a bad time, if possible.
*/
+ sigemptyset(&set);
+ sigaddset(&set,i);
+ sigprocmask(SIG_BLOCK, &set, &save);
+#endif
#if defined(FAKE_PERSISTENT_SIGNAL_HANDLERS) ||
defined(FAKE_DEFAULT_SIGNAL_HANDLERS)
if (!sig_handlers_initted) Perl_csighandler_init();
#endif
@@ -1189,17 +1232,23 @@
sig_defaulting[i] = 0;
#endif
SvREFCNT_dec(PL_psig_name[i]);
- SvREFCNT_dec(PL_psig_ptr[i]);
+ to_dec = PL_psig_ptr[i];
PL_psig_ptr[i] = SvREFCNT_inc(sv);
SvTEMP_off(sv); /* Make sure it doesn't go away on us */
PL_psig_name[i] = newSVpvn(s, len);
SvREADONLY_on(PL_psig_name[i]);
}
if (SvTYPE(sv) == SVt_PVGV || SvROK(sv)) {
- if (i)
+ if (i) {
(void)rsignal(i, &Perl_csighandler);
+#ifdef HAS_SIGPROCMASK
+ sigprocmask(SIG_SETMASK, &save, NULL);
+#endif
+ }
else
*svp = SvREFCNT_inc(sv);
+ if(to_dec)
+ SvREFCNT_dec(to_dec);
return 0;
}
s = SvPV_force(sv,len);
@@ -1212,7 +1261,7 @@
(void)rsignal(i, SIG_IGN);
#endif
} else
- *svp = 0;
+ *svp = 0; /* XXX: Redundant? */
}
else if (strEQ(s,"DEFAULT") || !*s) {
if (i)
@@ -1225,7 +1274,7 @@
(void)rsignal(i, SIG_DFL);
#endif
else
- *svp = 0;
+ *svp = 0; /* XXX: Redundant? */
}
else {
/*
@@ -1240,6 +1289,12 @@
else
*svp = SvREFCNT_inc(sv);
}
+#ifdef HAS_SIGPROCMASK
+ if(i)
+ sigprocmask(SIG_SETMASK, &save, NULL);
+#endif
+ if(to_dec)
+ SvREFCNT_dec(to_dec);
return 0;
}
#endif /* !PERL_MICRO */
diff -Naur perl-5.8.0/t/op/magic.t perl-5.8.0-sig2/t/op/magic.t
--- perl-5.8.0/t/op/magic.t Wed Jul 10 17:18:07 2002
+++ perl-5.8.0-sig2/t/op/magic.t Wed Jan 29 13:00:40 2003
@@ -36,7 +36,7 @@
return 1;
}
-print "1..46\n";
+print "1..48\n";
$Is_MSWin32 = $^O eq 'MSWin32';
$Is_NetWare = $^O eq 'NetWare';
@@ -67,7 +67,7 @@
close FOO; # just mention it, squelch used-only-once
if ($Is_MSWin32 || $Is_NetWare || $Is_Dos || $Is_MPE || $Is_MacOS) {
- skip('SIGINT not safe on this platform') for 1..2;
+ skip('SIGINT not safe on this platform') for 1..4;
}
else {
# the next tests are done in a subprocess because sh spits out a
@@ -98,7 +98,35 @@
close CMDPIPE;
- $test += 2;
+ open( CMDPIPE, "| $PERL");
+ print CMDPIPE <<'END';
+
+ { package X;
+ sub DESTROY {
+ kill "INT",$$;
+ }
+ }
+ sub x {
+ my $x=bless [], 'X';
+ return sub { $x };
+ }
+ $| = 1; # command buffering
+ $SIG{"INT"} = "ok5";
+ {
+ local $SIG{"INT"}=x();
+ print ""; # Needed to expose failure in 5.8.0 (why?)
+ }
+ sleep 1;
+ delete $SIG{"INT"};
+ kill "INT",$$; sleep 1;
+ sub ok5 {
+ print "ok 5\n";
+ }
+END
+ close CMDPIPE;
+ print $? & 0xFF ? "ok 6\n" : "not ok 6\n";
+
+ $test += 4;
}
# can we slice ENV?
Here is the output from "perlbug -d":
---
Flags:
category=
severity=
---
Site configuration information for perl v5.8.0:
Configured by anders at Fri Nov 15 12:33:55 PST 2002.
Summary of my perl5 (revision 5.0 version 8 subversion 0) configuration:
Platform:
osname=linux, osvers=2.4.18, archname=i686-linux
uname='linux wolf12 2.4.18 #1 mon jul 8 14:56:03 pdt 2002 i686
unknown '
config_args='-de'
hint=recommended, useposix=true, d_sigaction=define
usethreads=undef use5005threads=undef useithreads=undef
usemultiplicity=undef
useperlio=define d_sfio=undef uselargefiles=define usesocks=undef
use64bitint=undef use64bitall=undef uselongdouble=undef
usemymalloc=n, bincompat5005=undef
Compiler:
cc='cc', ccflags ='-fno-strict-aliasing -I/usr/local/include
-D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64 -I/usr/include/gdbm',
optimize='-O2',
cppflags='-fno-strict-aliasing -I/usr/local/include
-I/usr/include/gdbm'
ccversion='', gccversion='2.96 20000731 (Red Hat Linux 7.1
2.96-98)', gccosandvers=''
intsize=4, longsize=4, ptrsize=4, doublesize=8, byteorder=1234
d_longlong=define, longlongsize=8, d_longdbl=define, longdblsize=12
ivtype='long', ivsize=4, nvtype='double', nvsize=8, Off_t='off_t',
lseeksize=8
alignbytes=4, prototype=define
Linker and Libraries:
ld='cc', ldflags =' -L/usr/local/lib'
libpth=/usr/local/lib /lib /usr/lib
libs=-lnsl -lndbm -lgdbm -ldl -lm -lc -lcrypt -lutil
perllibs=-lnsl -ldl -lm -lc -lcrypt -lutil
libc=/lib/libc-2.2.4.so, so=so, useshrplib=false, libperl=libperl.a
gnulibc_version='2.2.4'
Dynamic Linking:
dlsrc=dl_dlopen.xs, dlext=so, d_dlsymun=undef, ccdlflags='-rdynamic'
cccdlflags='-fpic', lddlflags='-shared -L/usr/local/lib'
Locally applied patches:
---
@INC for perl v5.8.0:
/tools/By-Install/perl/5.8.0/i686-linux2.4/1/lib/5.8.0/i686-linux
/tools/By-Install/perl/5.8.0/i686-linux2.4/1/lib/5.8.0
/tools/By-Install/cpan/living/i686-linux2.4/1/lib/cpan/i686-linux
/tools/By-Install/cpan/living/i686-linux2.4/1/lib/cpan
/tools/By-Install/cpan/living/i686-linux2.4/1/lib/cpan
.
---
Environment for perl v5.8.0:
HOME=/home1/anders
LANG=en_US
LANGUAGE (unset)
LD_LIBRARY_PATH=/opt/cadence/linux/ldv-3.4/tools/lib:/opt/cadence/linux/
ldv-3.4/tools/inca/lib:/usr/local/lib
LOGDIR (unset)
PATH=/home1/anders/bin:/tools/bin:/opt/cadence/linux/ldv-3.4/tools/bin:/
opt/cadence/linux/ldv-3.4/tools/inca/bin:/opt/synopsys/linux/vcs/bin:/op
t/synopsys/linux/vcs/virsimdir/bin:/usr/local/vnc:/opt/synopsys/linux/sc
l/linux/bin:/usr/local/bin:/bin:/usr/bin:/usr/X11R6/bin:.
PERLDOC_PAGER=less -Cr
PERL_BADLANG (unset)
SHELL=/bin/csh
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