[src/trunk]: src/libexec/ld.elf_so Introduce intermediate locking for fork, s...

[joerg <joerg%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/90e67f1b3d62
branches:  trunk
changeset: 1009205:90e67f1b3d62
user:      joerg <joerg%NetBSD.org@localhost>
date:      Thu Apr 16 14:39:58 2020 +0000

description:
Introduce intermediate locking for fork, so that the dynamic linker is
in a consistent state. This most importantly avoids races between dlopen
and friends and fork, potentially resulting in dead locks in the child
when it itself tries to acquire locks.

diffstat:

 lib/libc/gen/pthread_atfork.c |  13 ++++++++++---
 libexec/ld.elf_so/rtld.c      |  19 +++++++++++++++++--
 libexec/ld.elf_so/rtld.h      |   4 +++-
 libexec/ld.elf_so/symbols.map |   1 +
 4 files changed, 31 insertions(+), 6 deletions(-)

diffs (109 lines):

diff -r 45add3d9af40 -r 90e67f1b3d62 lib/libc/gen/pthread_atfork.c
--- a/lib/libc/gen/pthread_atfork.c     Thu Apr 16 09:51:56 2020 +0000
+++ b/lib/libc/gen/pthread_atfork.c     Thu Apr 16 14:39:58 2020 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: pthread_atfork.c,v 1.12 2020/02/01 18:14:16 kamil Exp $        */
+/*     $NetBSD: pthread_atfork.c,v 1.13 2020/04/16 14:39:58 joerg Exp $        */
 
 /*-
  * Copyright (c) 2002 The NetBSD Foundation, Inc.
@@ -31,7 +31,7 @@
 
 #include <sys/cdefs.h>
 #if defined(LIBC_SCCS) && !defined(lint)
-__RCSID("$NetBSD: pthread_atfork.c,v 1.12 2020/02/01 18:14:16 kamil Exp $");
+__RCSID("$NetBSD: pthread_atfork.c,v 1.13 2020/04/16 14:39:58 joerg Exp $");
 #endif /* LIBC_SCCS and not lint */
 
 #include "namespace.h"
@@ -48,6 +48,13 @@
 #endif /* __weak_alias */
 
 pid_t  __fork(void);   /* XXX */
+pid_t  __atomic_fork(void) __weak; /* XXX */
+
+pid_t
+__atomic_fork(void)
+{
+       return __fork();
+}
 
 struct atfork_callback {
        SIMPLEQ_ENTRY(atfork_callback) next;
@@ -157,7 +164,7 @@
        SIMPLEQ_FOREACH(iter, &prepareq, next)
                (*iter->fn)();
 
-       ret = __fork();
+       ret = __atomic_fork();
 
        if (ret != 0) {
                /*
diff -r 45add3d9af40 -r 90e67f1b3d62 libexec/ld.elf_so/rtld.c
--- a/libexec/ld.elf_so/rtld.c  Thu Apr 16 09:51:56 2020 +0000
+++ b/libexec/ld.elf_so/rtld.c  Thu Apr 16 14:39:58 2020 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: rtld.c,v 1.203 2020/03/04 01:21:17 thorpej Exp $        */
+/*     $NetBSD: rtld.c,v 1.204 2020/04/16 14:39:58 joerg Exp $  */
 
 /*
  * Copyright 1996 John D. Polstra.
@@ -40,7 +40,7 @@
 
 #include <sys/cdefs.h>
 #ifndef lint
-__RCSID("$NetBSD: rtld.c,v 1.203 2020/03/04 01:21:17 thorpej Exp $");
+__RCSID("$NetBSD: rtld.c,v 1.204 2020/04/16 14:39:58 joerg Exp $");
 #endif /* not lint */
 
 #include <sys/param.h>
@@ -1532,6 +1532,21 @@
        _rtld_exclusive_exit(&mask);
 }
 
+pid_t __fork(void);
+
+__dso_public pid_t
+__atomic_fork(void)
+{
+       sigset_t mask;
+       pid_t result;
+
+       _rtld_exclusive_enter(&mask);
+       result = __fork();
+       _rtld_exclusive_exit(&mask);
+
+       return result;
+}
+
 /*
  * Error reporting function.  Use it like printf.  If formats the message
  * into a buffer, and sets things up so that the next call to dlerror()
diff -r 45add3d9af40 -r 90e67f1b3d62 libexec/ld.elf_so/rtld.h
--- a/libexec/ld.elf_so/rtld.h  Thu Apr 16 09:51:56 2020 +0000
+++ b/libexec/ld.elf_so/rtld.h  Thu Apr 16 14:39:58 2020 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: rtld.h,v 1.138 2020/02/29 04:24:33 kamil Exp $  */
+/*     $NetBSD: rtld.h,v 1.139 2020/04/16 14:39:58 joerg Exp $  */
 
 /*
  * Copyright 1996 John D. Polstra.
@@ -370,6 +370,8 @@
 __dso_public void *_dlauxinfo(void) __pure;
 __dso_public void __dl_cxa_refcount(void *addr, ssize_t delta);
 
+__dso_public pid_t __atomic_fork(void);
+
 #if defined(__ARM_EABI__) && !defined(__ARM_DWARF_EH__)
 /*
  * This is used by libgcc to find the start and length of the exception table
diff -r 45add3d9af40 -r 90e67f1b3d62 libexec/ld.elf_so/symbols.map
--- a/libexec/ld.elf_so/symbols.map     Thu Apr 16 09:51:56 2020 +0000
+++ b/libexec/ld.elf_so/symbols.map     Thu Apr 16 14:39:58 2020 +0000
@@ -23,5 +23,6 @@
     ___tls_get_addr;
     __gnu_Unwind_Find_exidx;
     __dl_cxa_refcount;
+    __atomic_fork;
   local: *;
 };