Fix a race when loading XS modules
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From 61d4c87c940fea028f08f27addc275b469320fda Mon Sep 17 00:00:00 2001
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From: David Mitchell <davem@iabyn.com>
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Date: Mon, 18 Feb 2019 09:19:38 +0000
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Subject: [PATCH] Perl_my_cxt_init: fix potential race condition
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MIME-Version: 1.0
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Content-Type: text/plain; charset=UTF-8
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Content-Transfer-Encoding: 8bit
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(Found by code inspection - I can't reproduce a failure)
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the MY_CXT subsystem, which allows per-thread pseudo-static variables,
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has a thread race condition.
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When a module is first loaded, it is allocated unique index (from
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PL_my_cxt_index++) which is assigned to the module's my_cxt_index static
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var.
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If two threads both try to load an XS module at the same time, its
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possible for one thread to set my_cxtp, then a second thread to overwrite
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it with a higher value, causing the first thread to use the wrong index
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into its local storage.
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Signed-off-by: Petr Písař <ppisar@redhat.com>
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---
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util.c | 17 +++++++++++++----
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1 file changed, 13 insertions(+), 4 deletions(-)
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diff --git a/util.c b/util.c
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index 5b6f4bfd27..ae86a8c4a4 100644
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--- a/util.c
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+++ b/util.c
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@@ -5218,10 +5218,16 @@ Perl_my_cxt_init(pTHX_ int *index, size_t size)
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dVAR;
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void *p;
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PERL_ARGS_ASSERT_MY_CXT_INIT;
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+ /* do initial check without locking.
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+ * -1: not allocated or another thread currently allocating
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+ * other: already allocated by another thread
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+ */
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if (*index == -1) {
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- /* this module hasn't been allocated an index yet */
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MUTEX_LOCK(&PL_my_ctx_mutex);
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- *index = PL_my_cxt_index++;
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+ /*now a stricter check with locking */
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+ if (*index == -1)
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+ /* this module hasn't been allocated an index yet */
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+ *index = PL_my_cxt_index++;
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MUTEX_UNLOCK(&PL_my_ctx_mutex);
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}
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@@ -5278,9 +5284,12 @@ Perl_my_cxt_init(pTHX_ const char *my_cxt_key, size_t size)
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index = Perl_my_cxt_index(aTHX_ my_cxt_key);
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if (index == -1) {
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- /* this module hasn't been allocated an index yet */
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MUTEX_LOCK(&PL_my_ctx_mutex);
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- index = PL_my_cxt_index++;
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+ /*now a stricter check with locking */
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+ index = Perl_my_cxt_index(aTHX_ my_cxt_key);
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+ if (index == -1)
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+ /* this module hasn't been allocated an index yet */
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+ index = PL_my_cxt_index++;
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MUTEX_UNLOCK(&PL_my_ctx_mutex);
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}
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--
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2.20.1
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@ -254,6 +254,9 @@ Patch52: perl-5.29.7-perl-131562-correct-large-line-numbers-copying-eval-
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# Fix setting magic when changing $^R, RT#133782, in upstream after 5.29.7
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# Fix setting magic when changing $^R, RT#133782, in upstream after 5.29.7
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Patch53: perl-5.28.1-perl-133782-set-magic-when-changing-R.patch
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Patch53: perl-5.28.1-perl-133782-set-magic-when-changing-R.patch
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# Fix a race when loading XS modules, in upstream after 5.29.7
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Patch54: perl-5.29.7-Perl_my_cxt_init-fix-potential-race-condition.patch
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# Link XS modules to libperl.so with EU::CBuilder on Linux, bug #960048
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# Link XS modules to libperl.so with EU::CBuilder on Linux, bug #960048
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Patch200: perl-5.16.3-Link-XS-modules-to-libperl.so-with-EU-CBuilder-on-Li.patch
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Patch200: perl-5.16.3-Link-XS-modules-to-libperl.so-with-EU-CBuilder-on-Li.patch
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@ -2860,6 +2863,7 @@ Perl extension for Version Objects
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%patch51 -p1
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%patch51 -p1
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%patch52 -p1
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%patch52 -p1
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%patch53 -p1
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%patch53 -p1
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%patch54 -p1
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%patch200 -p1
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%patch200 -p1
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%patch201 -p1
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%patch201 -p1
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@ -2906,6 +2910,7 @@ perl -x patchlevel.h \
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'Fedora Patch51: Fix the interpreter path if procfs is not mounted (RT#133573)' \
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'Fedora Patch51: Fix the interpreter path if procfs is not mounted (RT#133573)' \
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'Fedora Patch52: Fix a crash when parsing #line directives with large numbers in eval (RT#131562)' \
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'Fedora Patch52: Fix a crash when parsing #line directives with large numbers in eval (RT#131562)' \
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'Fedora Patch53: Fix setting magic when changing $^R (RT#133782)' \
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'Fedora Patch53: Fix setting magic when changing $^R (RT#133782)' \
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'Fedora Patch54: Fix a race when loading XS modules' \
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'Fedora Patch200: Link XS modules to libperl.so with EU::CBuilder on Linux' \
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'Fedora Patch200: Link XS modules to libperl.so with EU::CBuilder on Linux' \
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'Fedora Patch201: Link XS modules to libperl.so with EU::MM on Linux' \
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'Fedora Patch201: Link XS modules to libperl.so with EU::MM on Linux' \
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%{nil}
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%{nil}
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@ -5198,6 +5203,7 @@ popd
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- Fix a crash when parsing #line directives with large numbers in eval
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- Fix a crash when parsing #line directives with large numbers in eval
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(RT#131562)
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(RT#131562)
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- Fix setting magic when changing $^R (RT#133782)
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- Fix setting magic when changing $^R (RT#133782)
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- Fix a race when loading XS modules
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* Fri Feb 01 2019 Fedora Release Engineering <releng@fedoraproject.org> - 4:5.28.1-432
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* Fri Feb 01 2019 Fedora Release Engineering <releng@fedoraproject.org> - 4:5.28.1-432
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- Rebuilt for https://fedoraproject.org/wiki/Fedora_30_Mass_Rebuild
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- Rebuilt for https://fedoraproject.org/wiki/Fedora_30_Mass_Rebuild
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