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libio: Fix a deadlock after fork in popen

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libio: Correctly link tst-popen-fork against libpthread (RHEL-86018)

Resolves: RHEL-86018
This commit is contained in:
Patsy Griffin 2025-04-25 09:37:32 -04:00
parent 01b9bca186
commit 68ae5c20b5
3 changed files with 230 additions and 1 deletions
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194
glibc-RHEL-86018-1.patch Normal file
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@ -0,0 +1,194 @@
commit 9f0d2c0ee6c728643fcf9a4879e9f20f5e45ce5f
Author: Arjun Shankar <arjun@redhat.com>
Date: Fri Oct 18 16:03:25 2024 +0200
libio: Fix a deadlock after fork in popen
popen modifies its file handler book-keeping under a lock that wasn't
being taken during fork. This meant that a concurrent popen and fork
could end up copying the lock in a "locked" state into the fork child,
where subsequently calling popen would lead to a deadlock due to the
already (spuriously) held lock.
This commit fixes the deadlock by appropriately taking the lock before
fork, and releasing/resetting it in the parent/child after the fork.
A new test for concurrent popen and fork is also added. It consistently
hangs (and therefore fails via timeout) without the fix applied.
Reviewed-by: Florian Weimer <fweimer@redhat.com>
Conflicts:
libio/Makefile
(Usual conflict when adding tests due to missing backports.)
posix/fork.c
(reworked due to file rename upstream and libpthread integration)
diff -Nrup a/libio/Makefile b/libio/Makefile
--- a/libio/Makefile 2025-04-23 15:51:08.439579602 -0400
+++ b/libio/Makefile 2025-04-23 15:11:32.124866600 -0400
@@ -62,7 +62,7 @@ tests = tst_swprintf tst_wprintf tst_sws
tst-memstream1 tst-memstream2 tst-memstream3 \
tst-wmemstream1 tst-wmemstream2 tst-wmemstream3 \
bug-memstream1 bug-wmemstream1 \
- tst-setvbuf1 tst-popen1 tst-fgetwc bug-wsetpos tst-fseek \
+ tst-setvbuf1 tst-popen-fork tst-popen1 tst-fgetwc bug-wsetpos tst-fseek \
tst-fwrite-error tst-ftell-partial-wide tst-ftell-active-handler \
tst-ftell-append tst-fputws tst-bz22415 tst-fgetc-after-eof \
tst-wfile-sync
diff -Nrup a/libio/iopopen.c b/libio/iopopen.c
--- a/libio/iopopen.c 2025-04-23 15:51:09.145583660 -0400
+++ b/libio/iopopen.c 2025-04-23 15:07:45.167549822 -0400
@@ -60,6 +60,26 @@ unlock (void *not_used)
}
#endif
+/* These lock/unlock/resetlock functions are used during fork. */
+
+void
+_IO_proc_file_chain_lock (void)
+{
+ _IO_lock_lock (proc_file_chain_lock);
+}
+
+void
+_IO_proc_file_chain_unlock (void)
+{
+ _IO_lock_unlock (proc_file_chain_lock);
+}
+
+void
+_IO_proc_file_chain_resetlock (void)
+{
+ _IO_lock_init (proc_file_chain_lock);
+}
+
/* POSIX states popen shall ensure that any streams from previous popen()
calls that remain open in the parent process should be closed in the new
child process.
diff -Nrup a/libio/libioP.h b/libio/libioP.h
--- a/libio/libioP.h 2025-04-23 15:51:08.012577147 -0400
+++ b/libio/libioP.h 2025-04-23 15:07:45.167549822 -0400
@@ -423,6 +423,12 @@ libc_hidden_proto (_IO_list_resetlock)
extern void _IO_enable_locks (void) __THROW;
libc_hidden_proto (_IO_enable_locks)
+/* Functions for operating popen's proc_file_chain_lock during fork. */
+
+extern void _IO_proc_file_chain_lock (void) __THROW attribute_hidden;
+extern void _IO_proc_file_chain_unlock (void) __THROW attribute_hidden;
+extern void _IO_proc_file_chain_resetlock (void) __THROW attribute_hidden;
+
/* Default jumptable functions. */
extern int _IO_default_underflow (FILE *) __THROW;
diff -Nrup a/libio/tst-popen-fork.c b/libio/tst-popen-fork.c
--- a/libio/tst-popen-fork.c 1969-12-31 19:00:00.000000000 -0500
+++ b/libio/tst-popen-fork.c 2025-04-23 15:07:45.168549828 -0400
@@ -0,0 +1,80 @@
+/* Test concurrent popen and fork.
+ Copyright (C) 2024 Free Software Foundation, Inc.
+ This file is part of the GNU C Library.
+
+ The GNU C Library is free software; you can redistribute it and/or
+ modify it under the terms of the GNU Lesser General Public
+ License as published by the Free Software Foundation; either
+ version 2.1 of the License, or (at your option) any later version.
+
+ The GNU C Library is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ Lesser General Public License for more details.
+
+ You should have received a copy of the GNU Lesser General Public
+ License along with the GNU C Library; if not, see
+ <https://www.gnu.org/licenses/>. */
+
+#include <stdio.h>
+#include <stdatomic.h>
+#include <pthread.h>
+#include <unistd.h>
+#include <sys/wait.h>
+
+#include <support/check.h>
+#include <support/xthread.h>
+#include <support/xunistd.h>
+
+static void
+popen_and_pclose (void)
+{
+ FILE *f = popen ("true", "r");
+ TEST_VERIFY_EXIT (f != NULL);
+ pclose (f);
+ return;
+}
+
+static atomic_bool done = ATOMIC_VAR_INIT (0);
+
+static void *
+popen_and_pclose_forever (__attribute__ ((unused))
+ void *arg)
+{
+ while (!atomic_load_explicit (&done, memory_order_acquire))
+ popen_and_pclose ();
+ return NULL;
+}
+
+static int
+do_test (void)
+{
+
+ /* Repeatedly call popen in a loop during the entire test. */
+ pthread_t t = xpthread_create (NULL, popen_and_pclose_forever, NULL);
+
+ /* Repeatedly fork off and reap child processes one-by-one.
+ Each child calls popen once, then exits, leading to the possibility
+ that a child forks *during* our own popen call, thus inheriting any
+ intermediate popen state, possibly including lock state(s). */
+ for (int i = 0; i < 100; i++)
+ {
+ int cpid = xfork ();
+
+ if (cpid == 0)
+ {
+ popen_and_pclose ();
+ _exit (0);
+ }
+ else
+ xwaitpid (cpid, NULL, 0);
+ }
+
+ /* Stop calling popen. */
+ atomic_store_explicit (&done, 1, memory_order_release);
+ xpthread_join (t);
+
+ return 0;
+}
+
+#include <support/test-driver.c>
--- a/sysdeps/nptl/fork.c 2025-04-23 16:33:49.283403134 -0400
+++ b/sysdeps/nptl/fork.c 2025-04-23 16:33:12.240190356 -0400
@@ -65,6 +65,7 @@ __libc_fork (void)
not matter if fork was called from a signal handler. */
if (multiple_threads)
{
+ _IO_proc_file_chain_lock ();
_IO_list_lock ();
/* Acquire malloc locks. This needs to come last because fork
@@ -121,6 +122,7 @@ __libc_fork (void)
/* Reset locks in the I/O code. */
_IO_list_resetlock ();
+ _IO_proc_file_chain_resetlock ();
}
/* Reset the lock the dynamic loader uses to protect its data. */
@@ -142,6 +144,7 @@ __libc_fork (void)
/* We execute this even if the 'fork' call failed. */
_IO_list_unlock ();
+ _IO_proc_file_chain_unlock ();
}
/* Run the handlers registered for the parent. */

29
glibc-RHEL-86018-2.patch Normal file
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@ -0,0 +1,29 @@
commit 6a290b2895b77be839fcb7c44a6a9879560097ad
Author: Arjun Shankar <arjun@redhat.com>
Date: Fri Oct 25 09:33:45 2024 +0200
libio: Correctly link tst-popen-fork against libpthread
tst-popen-fork failed to build for Hurd due to not being linked with
libpthread. This commit fixes that.
Tested with build-many-glibcs.py for i686-gnu.
Reviewed-by: Florian Weimer <fweimer@redhat.com>
Conflicts:
libio/Makefile
(Usual conflict when adding tests due to missing backports.)
diff -Nrup a/libio/Makefile b/libio/Makefile
--- a/libio/Makefile 2025-04-23 16:41:58.028210552 -0400
+++ b/libio/Makefile 2025-04-23 16:41:30.195050679 -0400
@@ -67,6 +67,8 @@ tests = tst_swprintf tst_wprintf tst_sws
tst-ftell-append tst-fputws tst-bz22415 tst-fgetc-after-eof \
tst-wfile-sync
+$(objpfx)tst-popen-fork: $(shared-thread-library)
+
tests-internal = tst-vtables tst-vtables-interposed
ifeq (yes,$(build-shared))

8
glibc.spec
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@ -115,7 +115,7 @@ end \
Summary: The GNU libc libraries
Name: glibc
Version: %{glibcversion}
Release: %{glibcrelease}.18
Release: %{glibcrelease}.19
# In general, GPLv2+ is used by programs, LGPLv2+ is used for
# libraries.
@ -1264,6 +1264,8 @@ Patch1029: glibc-RHEL-83306-2.patch
Patch1030: glibc-RHEL-35280.patch
Patch1031: glibc-RHEL-76211.patch
Patch1032: glibc-RHEL-76387.patch
Patch1033: glibc-RHEL-86018-1.patch
Patch1034: glibc-RHEL-86018-2.patch
##############################################################################
# Continued list of core "glibc" package information:
@ -2925,6 +2927,10 @@ fi
%{_libdir}/libpthread_nonshared.a
%changelog
* Fri Apr 25 2025 Patsy Griffin <patsy@redhat.com> - 2.28-251.19
- libio: Fix a deadlock after fork in popen
- libio: Correctly link tst-popen-fork against libpthread (RHEL-86018)
* Fri Apr 18 2025 Patsy Griffin <patsy@redhat.com> - 2.28-251.18
- x86: Avoid integer truncation with large cache sizes (RHEL-76387)