[PATCH] 5.28.1: $^X is undefined on Linux without /proc #16808

p5pRT · 2019-01-12T15:58:09Z

Migrated from rt.perl.org#133765 (status was 'open')

Searchable as RT133765$

p5pRT · 2019-01-12T15:58:09Z

From viy@altlinux.org

This is a bug report for perl from viy@altlinux.org,
generated with the help of perlbug 1.40 running under perl 5.22.3.

On normal system
$ perl -le 'use warnings; print $^X'
/usr/bin/perl5.28.1

In a chroot without /proc or just with sudo umount /proc
$ perl -le 'use warnings; print $^X'
Use of uninitialized value ...

Current implementation of $^X assumes that /proc/self/exe
is always available and accessible on Linux.
It is not true; For example, in ALT Linux
secure chroot build environment does not mount /proc
by default.
Other example is early stages of system initialization
or system boot failure where /proc is not yet mounted
or failed to mount.

In that case, $^X should be PL_origargv[0].
Instead, it is undefined.

As a result, perl tools can fail or change its behaviour.

for example, now ExtUtils::MakeMaker fails without /proc:
+ /usr/bin/perl Makefile.PL PREFIX=/usr INSTALLDIRS=vendor
Use of uninitialized value $_[0] in substitution (s///) at /usr/share/perl5/File/Basename.pm line 341.
fileparse(): need a valid pathname at /usr/share/perl5/ExtUtils/MM_Unix.pm line 1128.
[...]
and perl modules can not be built in chroot without /proc.
It is regression compared to perl 5.26.

Proposed patch (tested)

Inline Patch

diff --git a/caretx.c b/caretx.c
index d758f73..aa069cc 100644
--- a/caretx.c
+++ b/caretx.c
@@ -97,7 +97,15 @@ Perl_set_caret_X(pTHX) {
     }
 #elif defined(HAS_PROCSELFEXE)
     char buf[MAXPATHLEN];
-    SSize_t len = readlink(PROCSELFEXE_PATH, buf, sizeof(buf) - 1);
+    SSize_t len;
+    /* NOTE: it is possible for /proc to be unmounted
+     * or for perl to be run in a chroot environment without /proc . */
+    if (access(PROCSELFEXE_PATH, R_OK) != 0) {
+	/* Fallback */
+	sv_setpv(caret_x, PL_origargv[0]);
+	return;
+    }
+    len = readlink(PROCSELFEXE_PATH, buf, sizeof(buf) - 1);
     /* NOTE: if the length returned by readlink() is sizeof(buf) - 1,
      * it is impossible to know whether the result was truncated. */
 
---

Flags: category=core severity=high Type=Patch PatchStatus=HasPatch

Site configuration information for perl 5.22.3:

Configured by ALT Linux Team at Wed Feb 1 13:44:57 UTC 2017.

Summary of my perl5 (revision 5 version 22 subversion 3) configuration:

Platform:
osname=linux, osvers=4.4.42-std-def-alt1.1, archname=x86_64-linux-thread-multi
uname='linux localhost.localdomain 4.4.42-std-def-alt1.1 #1 smp fri jan 13 06:15:14 utc 2017 x86_64 gnulinux '
config_args='-ders -Dusethreads -Duseithreads -Duselargefiles -Duseshrplib -Dlibperl=libperl-5.22.so -Dcc=gcc -Doptimize=-pipe -Wall -g -O2 -DDEBUGGING=maybe -Dprefix=/usr -Dprivlib=/usr/share/perl5 -Darchlib=/usr/lib64/perl5 -Dvendorprefix=/usr -Dvendorlib=/usr/share/perl5 -Dvendorarch=/usr/lib64/perl5 -Dsiteprefix=/usr/local -Dsitelib=/usr/local/share/perl/5.22 -Dsitearch=/usr/local/lib64/perl/5.22 -Dotherlibdirs=/etc/perl5:/usr/lib/perl5/vendor_perl -Dinc_version_list=none -Dpager=/usr/bin/less -isR -Dman1dir=/usr/share/man/man1 -Dman3dir=none -Dcf_by=ALT Linux Team -Dcf_email=Perl Maintainers Team <cpan@altlinux.ru> -Dmyhostname=localhost -Dperladmin=root@localhost'
hint=recommended, useposix=true, d_sigaction=define
useithreads=define, usemultiplicity=define
use64bitint=define, use64bitall=define, uselongdouble=undef
usemymalloc=n, bincompat5005=undef
Compiler:
cc='gcc', ccflags ='-D_REENTRANT -D_GNU_SOURCE -fwrapv -fno-strict-aliasing -pipe -fstack-protector-strong -I/usr/local/include -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64',
optimize='-pipe -Wall -g -O2',
cppflags='-D_REENTRANT -D_GNU_SOURCE -fwrapv -fno-strict-aliasing -pipe -fstack-protector-strong -I/usr/local/include'
ccversion='', gccversion='5.3.1 20151207 (ALT Linux 5.3.1-alt3)', gccosandvers=''
intsize=4, longsize=8, ptrsize=8, doublesize=8, byteorder=12345678, doublekind=3
d_longlong=define, longlongsize=8, d_longdbl=define, longdblsize=16, longdblkind=3
ivtype='long', ivsize=8, nvtype='double', nvsize=8, Off_t='off_t', lseeksize=8
alignbytes=8, prototype=define
Linker and Libraries:
ld='gcc', ldflags =' -fstack-protector-strong -L/usr/local/lib'
libpth=/usr/local/lib /usr/lib /lib64 /usr/lib64 /lib /usr/local/lib64
libs=-lpthread -lnsl -lgdbm -ldb -ldl -lm -lcrypt -lutil -lc -lgdbm_compat
perllibs=-lpthread -lnsl -ldl -lm -lcrypt -lutil -lc
libc=libc-2.23.so, so=so, useshrplib=true, libperl=libperl-5.22.so
gnulibc_version='2.23'
Dynamic Linking:
dlsrc=dl_dlopen.xs, dlext=so, d_dlsymun=undef, ccdlflags='-Wl,-E'
cccdlflags='-fPIC', lddlflags='-shared -pipe -Wall -g -O2 -L/usr/local/lib -fstack-protector-strong'

@INC for perl 5.22.3:
/usr/local/lib64/perl/5.22
/usr/local/share/perl/5.22
/usr/lib64/perl5
/usr/share/perl5
/usr/lib64/perl5
/usr/share/perl5
/etc/perl5
/usr/lib/perl5/vendor_perl

Environment for perl 5.22.3:
HOME=/home/cpanbuilder
LANG=ru_RU.UTF-8
LANGUAGE (unset)
LD_LIBRARY_PATH (unset)
LOGDIR (unset)
PATH=/home/cpanbuilder/bin:/bin:/usr/bin:/usr/local/bin:/usr/X11R6/bin:/usr/games
PERL_BADLANG (unset)
SHELL=/bin/bash

p5pRT · 2019-01-12T15:58:09Z

From viy@altlinux.org

perl-5.28.1-alt-viy-caretx-chroot-support.patch

diff --git a/caretx.c b/caretx.c
index d758f73..aa069cc 100644
--- a/caretx.c
+++ b/caretx.c
@@ -97,7 +97,15 @@ Perl_set_caret_X(pTHX) {
     }
 #elif defined(HAS_PROCSELFEXE)
     char buf[MAXPATHLEN];
-    SSize_t len = readlink(PROCSELFEXE_PATH, buf, sizeof(buf) - 1);
+    SSize_t len;
+    /* NOTE: it is possible for /proc to be unmounted
+     * or for perl to be run in a chroot environment without /proc . */
+    if (access(PROCSELFEXE_PATH, R_OK) != 0) {
+	/* Fallback */
+	sv_setpv(caret_x, PL_origargv[0]);
+	return;
+    }
+    len = readlink(PROCSELFEXE_PATH, buf, sizeof(buf) - 1);
     /* NOTE: if the length returned by readlink() is sizeof(buf) - 1,
      * it is impossible to know whether the result was truncated. */

p5pRT · 2019-01-12T16:14:35Z

From viy@altlinux.org

It is my first time reporting to rt.perl.org/,
I used perlbug on the build machine with older perl,
but this bug is about perl 5.28.1.

p5pRT · 2019-01-14T22:43:28Z

From @tonycoz

On Sat, 12 Jan 2019 07:58:09 -0800, viy@altlinux.org wrote:

This is a bug report for perl from viy@altlinux.org,
generated with the help of perlbug 1.40 running under perl 5.22.3.

On normal system
$ perl -le 'use warnings; print $^X'
/usr/bin/perl5.28.1

In a chroot without /proc or just with sudo umount /proc
$ perl -le 'use warnings; print $^X'
Use of uninitialized value ...

Current implementation of $^X assumes that /proc/self/exe
is always available and accessible on Linux.
It is not true; For example, in ALT Linux
secure chroot build environment does not mount /proc
by default.
Other example is early stages of system initialization
or system boot failure where /proc is not yet mounted
or failed to mount.

In that case, $^X should be PL_origargv[0].
Instead, it is undefined.

As a result, perl tools can fail or change its behaviour.

for example, now ExtUtils::MakeMaker fails without /proc:
+ /usr/bin/perl Makefile.PL PREFIX=/usr INSTALLDIRS=vendor
Use of uninitialized value $_[0] in substitution (s///) at
/usr/share/perl5/File/Basename.pm line 341.
fileparse(): need a valid pathname at
/usr/share/perl5/ExtUtils/MM_Unix.pm line 1128.
[...]
and perl modules can not be built in chroot without /proc.
It is regression compared to perl 5.26.

The code already has a fallback to:

sv_setpv(caret_x, PL_origargv[0]);

if the readlink() fails, which it should if /proc isn't mounted.

If that's not happening can you produce a relevant strace?

Thanks,
Tony

p5pRT · 2019-01-14T22:43:28Z

The RT System itself - Status changed from 'new' to 'open'

p5pRT · 2019-01-15T00:41:35Z

From @ilmari

"Tony Cook via RT" <perlbug-followup@perl.org> writes:

On Sat, 12 Jan 2019 07:58:09 -0800, viy@altlinux.org wrote:

This is a bug report for perl from viy@altlinux.org,
generated with the help of perlbug 1.40 running under perl 5.22.3.

On normal system
$ perl -le 'use warnings; print $^X'
/usr/bin/perl5.28.1

In a chroot without /proc or just with sudo umount /proc
$ perl -le 'use warnings; print $^X'
Use of uninitialized value ...

Current implementation of $^X assumes that /proc/self/exe
is always available and accessible on Linux.
It is not true; For example, in ALT Linux
secure chroot build environment does not mount /proc
by default.
Other example is early stages of system initialization
or system boot failure where /proc is not yet mounted
or failed to mount.

In that case, $^X should be PL_origargv[0].
Instead, it is undefined.

As a result, perl tools can fail or change its behaviour.

for example, now ExtUtils::MakeMaker fails without /proc:
+ /usr/bin/perl Makefile.PL PREFIX=/usr INSTALLDIRS=vendor
Use of uninitialized value $_[0] in substitution (s///) at
/usr/share/perl5/File/Basename.pm line 341.
fileparse(): need a valid pathname at
/usr/share/perl5/ExtUtils/MM_Unix.pm line 1128.
[...]
and perl modules can not be built in chroot without /proc.
It is regression compared to perl 5.26.

The code already has a fallback to:

sv_setpv(caret_x, PL_origargv[0]);

if the readlink() fails, which it should if /proc isn't mounted.

If that's not happening can you produce a relevant strace?

It does now, but didn't in 5.28, c.f.
https://rt.perl.org/Public/Bug/Display.html?id=133573 and
https://perl5.git.perl.org/perl.git/commitdiff/03b94aa47e981af3c7b0118bfb11facda2b95251

Since this was a regression in 5.28 (introduced in
https://perl5.git.perl.org/perl.git/commitdiff/fca5fb9612a125f48173bedf2c079778d7bc54dd),
I reckon the fix is eligible for backporting.

- ilmari
--
"I use RMS as a guide in the same way that a boat captain would use
a lighthouse. It's good to know where it is, but you generally
don't want to find yourself in the same spot." - Tollef Fog Heen

p5pRT · 2019-01-15T03:31:27Z

From @tonycoz

On Mon, 14 Jan 2019 16:41:35 -0800, ilmari wrote:

"Tony Cook via RT" <perlbug-followup@perl.org> writes:

On Sat, 12 Jan 2019 07:58:09 -0800, viy@altlinux.org wrote:

This is a bug report for perl from viy@altlinux.org,
generated with the help of perlbug 1.40 running under perl 5.22.3.

On normal system
$ perl -le 'use warnings; print $^X'
/usr/bin/perl5.28.1

In a chroot without /proc or just with sudo umount /proc
$ perl -le 'use warnings; print $^X'
Use of uninitialized value ...

Current implementation of $^X assumes that /proc/self/exe
is always available and accessible on Linux.
It is not true; For example, in ALT Linux
secure chroot build environment does not mount /proc
by default.
Other example is early stages of system initialization
or system boot failure where /proc is not yet mounted
or failed to mount.

In that case, $^X should be PL_origargv[0].
Instead, it is undefined.

As a result, perl tools can fail or change its behaviour.

for example, now ExtUtils::MakeMaker fails without /proc:
+ /usr/bin/perl Makefile.PL PREFIX=/usr INSTALLDIRS=vendor
Use of uninitialized value $_[0] in substitution (s///) at
/usr/share/perl5/File/Basename.pm line 341.
fileparse(): need a valid pathname at
/usr/share/perl5/ExtUtils/MM_Unix.pm line 1128.
[...]
and perl modules can not be built in chroot without /proc.
It is regression compared to perl 5.26.

The code already has a fallback to:

sv_setpv(caret_x, PL_origargv[0]);

if the readlink() fails, which it should if /proc isn't mounted.

If that's not happening can you produce a relevant strace?

It does now, but didn't in 5.28, c.f.
https://rt.perl.org/Public/Bug/Display.html?id=133573 and
https://perl5.git.perl.org/perl.git/commitdiff/03b94aa47e981af3c7b0118bfb11facda2b95251

Since this was a regression in 5.28 (introduced in
https://perl5.git.perl.org/perl.git/commitdiff/fca5fb9612a125f48173bedf2c079778d7bc54dd),
I reckon the fix is eligible for backporting.

Thanks, I've added it to the votes file and voted for it in 758a695.

Tony

p5pRT added the Severity Low label Oct 19, 2019

xenu removed the Severity Low label Dec 29, 2021

khwilliamson added the hasPatch label Apr 17, 2022

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[PATCH] 5.28.1: $^X is undefined on Linux without /proc #16808

[PATCH] 5.28.1: $^X is undefined on Linux without /proc #16808

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[PATCH] 5.28.1: $^X is undefined on Linux without /proc #16808

[PATCH] 5.28.1: $^X is undefined on Linux without /proc #16808

Comments

p5pRT commented Jan 12, 2019

p5pRT commented Jan 12, 2019

From viy@altlinux.org

p5pRT commented Jan 12, 2019

From viy@altlinux.org

p5pRT commented Jan 12, 2019

From viy@altlinux.org

p5pRT commented Jan 14, 2019

From @tonycoz

p5pRT commented Jan 14, 2019

p5pRT commented Jan 15, 2019

From @ilmari

p5pRT commented Jan 15, 2019

From @tonycoz