NetBSD Problem Report #40220

From jmcneill@black.invisible.ca  Thu Dec 18 14:41:41 2008
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Date: Thu, 18 Dec 2008 09:41:21 -0500 (EST)
From: jmcneill@invisible.ca
Reply-To: jmcneill@invisible.ca
To: gnats-bugs@gnats.NetBSD.org
Subject: LD_PRELOAD with dlsym(RTLD_NEXT, "stat") recursion
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>Number:         40220
>Category:       lib
>Synopsis:       LD_PRELOAD with dlsym(RTLD_NEXT, "stat") recursion
>Confidential:   no
>Severity:       non-critical
>Priority:       medium
>Responsible:    lib-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Thu Dec 18 14:45:00 +0000 2008
>Last-Modified:  Sat Apr 18 18:00:02 +0000 2009
>Originator:     Jared D. McNeill
>Release:        NetBSD 5.99.5
>Organization:

>Environment:


System: NetBSD black.invisible.ca 5.99.5 NetBSD 5.99.5 (GENERIC) #39: Mon Dec 15 20:56:04 EST 2008 jmcneill@black.invisible.ca:/export/home/jmcneill/branches/HEAD/src/sys/arch/amd64/compile/GENERIC amd64
Architecture: x86_64
Machine: amd64
>Description:
	When trying to overload the 'stat' function with LD_PRELOAD,
	the overloaded function will end up recursing.
>How-To-Repeat:
	Compile the following program with:

	  $ cc -fPIC -DPIC -shared test.c -o test.so

	and then run:

	  $ LD_PRELOAD=test.so ls -l 
	  stat(/etc/nsswitch.conf) depth=1
	  stat(/etc/nsswitch.conf) depth=2
	  assertion "depth == 1" failed: file "test.c", line 20, function "stat"
	  Abort (core dumped) 

#include <sys/stat.h>
#include <assert.h>
#include <dlfcn.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

static int (*_stat)(const char *, struct stat *) = NULL;

int
stat(const char *pathname, struct stat *buf)
{
	static int depth = 0;
	int ret;

	++depth;
	(void)fprintf(stderr, "stat(%s) depth=%d\n", pathname, depth);

	assert(depth == 1);

	if (!_stat)
		_stat = dlsym(RTLD_NEXT, "stat");

	ret = _stat(pathname, buf);
	--depth;

	return ret;

}
>Fix:


>Audit-Trail:
From: "Jared D. McNeill" <jmcneill@netbsd.org>
To: gnats-bugs@gnats.NetBSD.org
Cc: 
Subject: PR/40220 CVS commit: pkgsrc/audio/pulseaudio
Date: Thu, 18 Dec 2008 18:43:52 +0000 (UTC)

 Module Name:	pkgsrc
 Committed By:	jmcneill
 Date:		Thu Dec 18 18:43:52 UTC 2008

 Modified Files:
 	pkgsrc/audio/pulseaudio: Makefile distinfo
 	pkgsrc/audio/pulseaudio/patches: patch-aa

 Log Message:
 Workaround PR lib/40220 on NetBSD, padsp (OSS wrapper) now works.
 Bump PKGREVISION.


 To generate a diff of this commit:
 cvs rdiff -r1.1.1.1 -r1.2 pkgsrc/audio/pulseaudio/Makefile \
     pkgsrc/audio/pulseaudio/distinfo
 cvs rdiff -r1.1.1.1 -r1.2 pkgsrc/audio/pulseaudio/patches/patch-aa

 Please note that diffs are not public domain; they are subject to the
 copyright notices on the relevant files.

From: Christian Biere <christianbiere@gmx.de>
To: gnats-bugs@gnats.NetBSD.org
Cc: 
Subject: Re: lib/40220: LD_PRELOAD with dlsym(RTLD_NEXT, "stat") recursion
Date: Sat, 18 Apr 2009 15:58:23 +0200

 I just noticed similar i.e., socker[1] doesn't work anymore when using
 the LD_PRELOAD wrapper on NetBSD. I've looked at the workaround in the
 pkgsrc patch.

 The workaround is to use "__stat30" instead of "stat" for dlsym().
 For socker I had to change "socket" to "__socket30".

 A quick check shows that a couple functions seem to be affected by
 this:

 $ nm /lib/libc.so|sed -n 's,^.* T __\(.*\)30$,\1,p'

 _readdir_unlocked
 fhstat
 fstat
 fts_children
 fts_close
 fts_open
 fts_read
 fts_set
 getdents
 getfh
 glob
 globfree
 lstat
 ntp_gettime
 opendir2
 opendir
 readdir
 readdir_r
 scandir
 socket
 stat

 Will this be fixed or are the "__.*30" names permanent?
 If these change the workaround will of course turn into a bug itself.

 [1] https://gtk-gnutella.svn.sourceforge.net/svnroot/gtk-gnutella/trunk/gtk-gnutella/contrib/socker/README
 -- 
 Christian

From: Martin Husemann <martin@duskware.de>
To: gnats-bugs@NetBSD.org
Cc: 
Subject: Re: lib/40220: LD_PRELOAD with dlsym(RTLD_NEXT, "stat") recursion
Date: Sat, 18 Apr 2009 19:56:54 +0200

 On Sat, Apr 18, 2009 at 02:00:06PM +0000, Christian Biere wrote:
 >  Will this be fixed or are the "__.*30" names permanent?
 >  If these change the workaround will of course turn into a bug itself.

 These are weak aliases, the functions had abi changes and have been renamed.
 This will stay this way untill libc gets it's major bumped.

 When compiling a wrapper you probably have to double check wether the
 rename/weak alias is in scope (i.e. avoid the official headers) or play
 ifdef games.

 Martin

>Unformatted:

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