[uml-devel] pcap cross-linking

[uml-devel] pcap cross-linking

[Antoine Martin]

Paolo,

pcap builds and runs fine on amd64 but there is a problem when building
with SUBARCH=i386: it uses the wrong version of libpcap.a:
ld -r -dp -o arch/um/drivers/pcap.o arch/um/drivers/pcap_kern.o
arch/um/drivers/pcap_user.o  -m elf_i386
-r /usr/lib/gcc/x86_64-pc-linux-gnu/3.4.4/../../../libpcap.a
Whereas the one it needs to link against is here:
/emul/linux/x86/usr/lib/libpcap.a

Fixing the Makefile is beyond me (probably not that hard), sorry - so I
link it manually. After that it works perfectly.

On the subject of pcap transport, I couldn't dig the email where you
suggested a way of figuring out which libraries should be placed in the
chroot, I tried to use the same libraries as I used on a 32-bit setup
but it fails to bring up the interface (when it works outside chroot).

I tried to guess and even added a few more, here is the chroot's /lib (I
made /lib64 a link to /lib in chroot):
ld-2.3.5.so           libcrack.so.2.8.0  libm.so.6
libnss_compat-2.3.5.so  libnss_hesiod-2.3.5.so   libpam.so
libpamc.so       libpcap.so.0.9      librt.so.1        security
ld-linux-x86-64.so.2  libcrypt-2.3.5.so  libncurses.so
libnss_compat.so.2      libnss_hesiod.so.2       libpam.so.0
libpamc.so.0     libpthread-0.10.so  libselinux.so.1   tls
libc-2.3.5.so         libcrypt.so.1      libncurses.so.5
libnss_dns-2.3.5.so     libnss_nis-2.3.5.so      libpam.so.0.78
libpamc.so.0.78  libpthread.so.0     libsemanage.so.1
libc.so.6             libdl-2.3.5.so     libncurses.so.5.4
libnss_dns.so.2         libnss_nis.so.2          libpam_misc.so
libpcap.a        libresolv-2.3.5.so  libsepol.so.1
libcrack.so           libdl.so.2         libnsl-2.3.5.so
libnss_files-2.3.5.so   libnss_nisplus-2.3.5.so  libpam_misc.so.0
libpcap.so       libresolv.so.2      libutil-2.3.5.so
libcrack.so.2         libm-2.3.5.so      libnsl.so.1
libnss_files.so.2       libnss_nisplus.so.2      libpam_misc.so.0.78
libpcap.so.0     librt-2.3.5.so      libutil.so.1
lib/tls:
libc-2.3.5.so  libc.so.6
(also lib/security so I can get into the chroot)
But that's not enough... and ldd didn't show me anything missing.
Any ideas?

Thanks
Antoine



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[uml-devel] Re: pcap cross-linking

[Blaisorblade]

On Sunday 18 December 2005 20:03, Antoine Martin wrote:
> Paolo,

> pcap builds and runs fine on amd64 but there is a problem when building
> with SUBARCH=i386: it uses the wrong version of libpcap.a:
> ld -r -dp -o arch/um/drivers/pcap.o arch/um/drivers/pcap_kern.o
> arch/um/drivers/pcap_user.o  -m elf_i386
> -r /usr/lib/gcc/x86_64-pc-linux-gnu/3.4.4/../../../libpcap.a

> Whereas the one it needs to link against is here:
> /emul/linux/x86/usr/lib/libpcap.a

This is IMHO a Gentoo bug - it is not setup for compilation of 32-bit binaries 
using anything else than glibc. I hit this problem with libncurses, when 
doing make menuconfig ARCH=um (now this was solved as helper programs are 
built as native again).

However, I built uml with libpcap by default for some time - possibly it was 
before me switching to 64-bit linux.

> Fixing the Makefile is beyond me (probably not that hard),

it is a bit hard - in this case it probably suffices to add -L searchpath 
(i.e. -L /emul/linux/x86/usr/lib/ ), but it's non-standard (aka only Gentoo 
works this way) - and merging fixes for every possible distro is not a good 
idea.

> sorry - so I 
> link it manually. After that it works perfectly.

> On the subject of pcap transport, I couldn't dig the email where you
> suggested a way of figuring out which libraries should be placed in the
> chroot, I tried to use the same libraries as I used on a 32-bit setup
> but it fails to bring up the interface (when it works outside chroot).

Don't know what I did suggest, but using strace -e open() (or, even better, 
ltrace -e dlopen ) would probably find the point where it's failing and the 
failed cmd line.

> I tried to guess and even added a few more, here is the chroot's /lib (I
> made /lib64 a link to /lib in chroot):
> ld-2.3.5.so           libcrack.so.2.8.0  libm.so.6

> libnss_compat-2.3.5.so  libnss_hesiod-2.3.5.so   libpam.so

Good thing, libnss_* is probably good - but don't forget /etc/nsswitch.conf 
and /etc/pam.d/* - /etc/pam.conf


> (also lib/security so I can get into the chroot)
That's for su, right? There are some tools (including "compartment") to 
combine chroot + su together.

> But that's not enough... and ldd didn't show me anything missing.

Ldd won't help you with dynamically loaded libraries.

Likely, a recursive "strings object|grep lib" will help - recursive means "do 
that also on libraries found this way".

Also, I see you're using SeLinux. I don't know anything about its library 
handling, and possibly it's going to make the story more difficult. However, 
strace/ltrace as suggested above should diagnose any problem.

-- 
Inform me of my mistakes, so I can keep imitating Homer Simpson's "Doh!".
Paolo Giarrusso, aka Blaisorblade (Skype ID "PaoloGiarrusso", ICQ 215621894)
http://www.user-mode-linux.org/~blaisorblade

	

	
		
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[uml-devel] Re: pcap cross-linking [PATCH]

[Antoine Martin]

[-- Attachment #1: Type: text/plain, Size: 2029 bytes --]

> > pcap builds and runs fine on amd64 but there is a problem when building
> > with SUBARCH=i386: it uses the wrong version of libpcap.a:
> > ld -r -dp -o arch/um/drivers/pcap.o arch/um/drivers/pcap_kern.o
> > arch/um/drivers/pcap_user.o  -m elf_i386
> > -r /usr/lib/gcc/x86_64-pc-linux-gnu/3.4.4/../../../libpcap.a
> 
> > Whereas the one it needs to link against is here:
> > /emul/linux/x86/usr/lib/libpcap.a
> 
> This is IMHO a Gentoo bug -
I'll ask the gentoo devs, for the time being I can copy this library
manually to /usr/lib32 (which is the standard location for 32-bit libs
on amd64)

But the problem remains, the linker should use:
-r /usr/lib32/libpcap.a
and not ../../../libpcap.a which ends up as /usr/lib (which points
to /usr/lib64 on standard distros)
But only when building with SUBARCH=i386. 

So I added this statement to the Makefile (patch attached) and now all
is well:
+ifeq ($(SUBARCH),i386)
+LDFLAGS_pcap.o := -r /usr/lib32/libpcap.a
+else

> Good thing, libnss_* is probably good - but don't forget /etc/nsswitch.conf 
> and /etc/pam.d/* - /etc/pam.conf
Yep, they're all there... see:
http://uml.nagafix.co.uk/SELinux/chroot/
This chroot example is here for SELinux but it applies just as well to
others.

I think I'll rebuild it with compartment and build su without pam to
trim it down even more.
> > (also lib/security so I can get into the chroot)
> That's for su, right? There are some tools (including "compartment") to 
> combine chroot + su together.
Yep, it's a shame compartment does not ship with all distros.
chroot without su is pointless (since you can use 'chroot-again' to
escape) changing uid/guid should really be included in chroot.

> Also, I see you're using SeLinux. I don't know anything about its library 
> handling, and possibly it's going to make the story more difficult.
It can do that... but the good thing is that it can be disabled.
>  However, 
> strace/ltrace as suggested above should diagnose any problem.
Cool - I'll try that and report back.

Many thanks
Antoine

[-- Attachment #2: uml-pcap-subarchi386-linkerfix.patch --]
[-- Type: text/x-patch, Size: 487 bytes --]

--- linux-2.6.15-rc6-x86-broken/arch/um/drivers/Makefile   2005-12-19 18:07:17.000000000 +0000
+++ linux-2.6.15-rc6-x86/arch/um/drivers/Makefile          2005-12-19 18:11:11.000000000 +0000
@@ -17,7 +17,11 @@
 port-objs := port_kern.o port_user.o
 harddog-objs := harddog_kern.o harddog_user.o

+ifeq ($(SUBARCH),i386)
+LDFLAGS_pcap.o := -r /usr/lib32/libpcap.a
+else
 LDFLAGS_pcap.o := -r $(shell $(CC) $(CFLAGS) -print-file-name=libpcap.a)
+endif

 targets := pcap_kern.o pcap_user.o

Re: [uml-devel] Re: pcap cross-linking [PATCH]

[Blaisorblade]

On Monday 19 December 2005 19:33, Antoine Martin wrote:
> > > pcap builds and runs fine on amd64 but there is a problem when building
> > > with SUBARCH=i386: it uses the wrong version of libpcap.a:
> > > ld -r -dp -o arch/um/drivers/pcap.o arch/um/drivers/pcap_kern.o
> > > arch/um/drivers/pcap_user.o  -m elf_i386
> > > -r /usr/lib/gcc/x86_64-pc-linux-gnu/3.4.4/../../../libpcap.a

> > > Whereas the one it needs to link against is here:
> > > /emul/linux/x86/usr/lib/libpcap.a

> > This is IMHO a Gentoo bug -

> I'll ask the gentoo devs, for the time being I can copy this library
> manually to /usr/lib32 (which is the standard location for 32-bit libs
> on amd64)

> But the problem remains, the linker should use:
> -r /usr/lib32/libpcap.a
> and not ../../../libpcap.a which ends up as /usr/lib (which points
> to /usr/lib64 on standard distros)
> But only when building with SUBARCH=i386.

> So I added this statement to the Makefile (patch attached) and now all
> is well:
> +ifeq ($(SUBARCH),i386)
> +LDFLAGS_pcap.o := -r /usr/lib32/libpcap.a
> +else

Yep, seen that - obviously this patch can't be merged as the thing is 
non-standard (not that I know, I just guess this). Just a first guess 
however.

Also, by gross testing on my system (guess Gentoo devs have screwed up 
something else on your system, too). Note the -m32 difference and lib32 vs. 
lib64:

$ gcc -print-file-name=libpcap.a
/usr/lib/gcc/x86_64-pc-linux-gnu/3.4.4/../../../../lib64/libpcap.a
$ gcc -m32 -print-file-name=libpcap.a
/usr/lib/gcc/x86_64-pc-linux-gnu/3.4.4/../../../../lib32/libpcap.a

> chroot without su is pointless (since you can use 'chroot-again' to
> escape)
Indeed.
-- 
Inform me of my mistakes, so I can keep imitating Homer Simpson's "Doh!".
Paolo Giarrusso, aka Blaisorblade (Skype ID "PaoloGiarrusso", ICQ 215621894)
http://www.user-mode-linux.org/~blaisorblade

	

	
		
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Re: [uml-devel] Re: pcap cross-linking [PATCH]

[Antoine Martin]

> > So I added this statement to the Makefile (patch attached) and now all
> > is well:
> > +ifeq ($(SUBARCH),i386)
> > +LDFLAGS_pcap.o := -r /usr/lib32/libpcap.a
> > +else
ahh, so this is the right way to find the lib... (cool)

> $ gcc -print-file-name=libpcap.a
> /usr/lib/gcc/x86_64-pc-linux-gnu/3.4.4/../../../../lib64/libpcap.a
> $ gcc -m32 -print-file-name=libpcap.a
> /usr/lib/gcc/x86_64-pc-linux-gnu/3.4.4/../../../../lib32/libpcap.a
Works for me (tm) too.
Can this be merged? (I can't see any reason not to now)

--- linux-2.6.15-rc6-x86-broken/arch/um/drivers/Makefile   2005-12-19
18:07:17.000000000 +0000
+++ linux-2.6.15-rc6-x86/arch/um/drivers/Makefile          2005-12-19 21:45:17.000000000 +0000
@@ -17,7 +17,11 @@
 port-objs := port_kern.o port_user.o
 harddog-objs := harddog_kern.o harddog_user.o

+ifeq ($(SUBARCH),i386)
+LDFLAGS_pcap.o := -r $(shell $(CC) $(CFLAGS) -m32 -print-file-name=libpcap.a)
+else
 LDFLAGS_pcap.o := -r $(shell $(CC) $(CFLAGS) -print-file-name=libpcap.a)
+endif

 targets := pcap_kern.o pcap_user.o



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Re: [uml-devel] Re: pcap cross-linking [PATCH]

[Blaisorblade]

On Monday 19 December 2005 22:47, Antoine Martin wrote:
> > > So I added this statement to the Makefile (patch attached) and now all
> > > is well:
> > > +ifeq ($(SUBARCH),i386)
> > > +LDFLAGS_pcap.o := -r /usr/lib32/libpcap.a
> > > +else
>
> ahh, so this is the right way to find the lib... (cool)

Suggested by Al Viro IIRC...

> > $ gcc -print-file-name=libpcap.a
> > /usr/lib/gcc/x86_64-pc-linux-gnu/3.4.4/../../../../lib64/libpcap.a
> > $ gcc -m32 -print-file-name=libpcap.a
> > /usr/lib/gcc/x86_64-pc-linux-gnu/3.4.4/../../../../lib32/libpcap.a
>
> Works for me (tm) too.

> Can this be merged? (I can't see any reason not to now)

Wait a moment - CFLAGS is supposed to contain -m32:

arch/um/Makefile-i386:

CFLAGS                  += $(call cc-option,-m32)

so there is something strange going on - but have you tested without this 
patch _after_ symlinking libraries into /usr/lib32?
-- 
Inform me of my mistakes, so I can keep imitating Homer Simpson's "Doh!".
Paolo Giarrusso, aka Blaisorblade (Skype ID "PaoloGiarrusso", ICQ 215621894)
http://www.user-mode-linux.org/~blaisorblade

	

	
		
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Re: [uml-devel] Re: pcap cross-linking [PATCH]

[Antoine Martin]

> > > $ gcc -print-file-name=libpcap.a
> > > /usr/lib/gcc/x86_64-pc-linux-gnu/3.4.4/../../../../lib64/libpcap.a
> > > $ gcc -m32 -print-file-name=libpcap.a
> > > /usr/lib/gcc/x86_64-pc-linux-gnu/3.4.4/../../../../lib32/libpcap.a
> >
> > Works for me (tm) too.
> 
> > Can this be merged? (I can't see any reason not to now)
> 
> Wait a moment - CFLAGS is supposed to contain -m32:
> 
> arch/um/Makefile-i386:
> 
> CFLAGS                  += $(call cc-option,-m32)
> 
> so there is something strange going on - but have you tested without this 
> patch _after_ symlinking libraries into /usr/lib32?
Yes, that works and in fact the patch solved nothing: I forgot to remove
the library from /usr/lib32 and that's what it used - DOH.
# gcc -m32 -print-file-name=libpcap.a
/usr/lib/gcc/x86_64-pc-linux-gnu/3.4.4/../../../libpcap.a
I thought the '-m32' would force it to try to find the 32 bit version?

So in the end the only way to get it to build is to copy the library
to /usr/lib32... no patch needed.

Antoine



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Re: [uml-devel] Re: pcap cross-linking [PATCH]

[Blaisorblade]

On Tuesday 20 December 2005 17:25, Antoine Martin wrote:
> > > > $ gcc -print-file-name=libpcap.a
> > > > /usr/lib/gcc/x86_64-pc-linux-gnu/3.4.4/../../../../lib64/libpcap.a
> > > > $ gcc -m32 -print-file-name=libpcap.a
> > > > /usr/lib/gcc/x86_64-pc-linux-gnu/3.4.4/../../../../lib32/libpcap.a
> > >
> > > Works for me (tm) too.
> > >
> > > Can this be merged? (I can't see any reason not to now)
> >
> > Wait a moment - CFLAGS is supposed to contain -m32:
> >
> > arch/um/Makefile-i386:
> >
> > CFLAGS                  += $(call cc-option,-m32)
> >
> > so there is something strange going on - but have you tested without this
> > patch _after_ symlinking libraries into /usr/lib32?
>
> Yes, that works and in fact the patch solved nothing: I forgot to remove
> the library from /usr/lib32 and that's what it used - DOH.
> # gcc -m32 -print-file-name=libpcap.a
> /usr/lib/gcc/x86_64-pc-linux-gnu/3.4.4/../../../libpcap.a
> I thought the '-m32' would force it to try to find the 32 bit version?

-m32 means "compile a 32bit program". Gcc is smart enough to correct the 
libraries search path. Gentoo is not smart enough to put emulation libraries 
in /usr/lib32.

Btw, which emul- package did you install to get libpcap? Also there's almost 
no .a file in /emul - they're intended to be used for .so (dynamic) libraries 
only, I guess - you sneaked it there, right?

However, the Gentoo bug is still there, and you followed its example in 
putting your libpcap.a.

I'm discussing the issue at:

http://bugs.gentoo.org/show_bug.cgi?id=100923

-- 
Inform me of my mistakes, so I can keep imitating Homer Simpson's "Doh!".
Paolo Giarrusso, aka Blaisorblade (Skype ID "PaoloGiarrusso", ICQ 215621894)
http://www.user-mode-linux.org/~blaisorblade

	

	
		
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Re: [uml-devel] Re: pcap cross-linking [PATCH]

[Rob Landley]

On Monday 19 December 2005 12:33, Antoine Martin wrote:
> I think I'll rebuild it with compartment and build su without pam to
> trim it down even more.
>
> > > (also lib/security so I can get into the chroot)
> >
> > That's for su, right? There are some tools (including "compartment") to
> > combine chroot + su together.
>
> Yep, it's a shame compartment does not ship with all distros.
> chroot without su is pointless (since you can use 'chroot-again' to
> escape) changing uid/guid should really be included in chroot.

This is the first I've heard of it, and after few minutes of googling the best 
I can find on it is this:
  http://www.suse.de/~marc/SuSE.html

Which is from February 2001.

Is that the newest version?

Rob
--
Steve Ballmer: Innovation!  Inigo Montoya: You keep using that word.
I do not think it means what you think it means.


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Re: [uml-devel] Re: pcap cross-linking [PATCH]

[Antoine Martin]

On Tue, 2005-12-20 at 14:01 -0600, Rob Landley wrote:
> On Monday 19 December 2005 12:33, Antoine Martin wrote:
> > Yep, it's a shame compartment does not ship with all distros.
> > chroot without su is pointless (since you can use 'chroot-again' to
> > escape) changing uid/guid should really be included in chroot.
> 
> This is the first I've heard of it, and after few minutes of googling the best 
> I can find on it is this:
>   http://www.suse.de/~marc/SuSE.html
> 
> Which is from February 2001.
> 
> Is that the newest version?
Probably, all it does is: chroot / change uid/gid:
chroot(chroot_path)
setgid(set_group)
setuid(set_user)
Looking at it, there is very little code in there - which is a good
thing! Less likely to go wrong.

Antoine



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Re: [uml-devel] Re: pcap cross-linking [PATCH]

[Blaisorblade]

[-- Attachment #1: Type: text/plain, Size: 1167 bytes --]

On Tuesday 20 December 2005 21:01, Rob Landley wrote:
> On Monday 19 December 2005 12:33, Antoine Martin wrote:
> > I think I'll rebuild it with compartment and build su without pam to
> > trim it down even more.

> > > > (also lib/security so I can get into the chroot)

> > > That's for su, right? There are some tools (including "compartment") to
> > > combine chroot + su together.

> > Yep, it's a shame compartment does not ship with all distros.
> > chroot without su is pointless (since you can use 'chroot-again' to
> > escape) changing uid/guid should really be included in chroot.

> This is the first I've heard of it, and after few minutes of googling the
> best I can find on it is this:
>   http://www.suse.de/~marc/SuSE.html

> Which is from February 2001.
> Is that the newest version?

Don't know, guess yes - and that's more or less the URL I had. I know it just 
because it was mentioned here (by Gerd Knorr, maybe - former SuSE UML 
maintainer).
-- 
Inform me of my mistakes, so I can keep imitating Homer Simpson's "Doh!".
Paolo Giarrusso, aka Blaisorblade (Skype ID "PaoloGiarrusso", ICQ 215621894)
http://www.user-mode-linux.org/~blaisorblade

[-- Attachment #2: chroot-setuid.c --]
[-- Type: text/x-csrc, Size: 669 bytes --]

#include <stdio.h>
#include <errno.h>
#include <stdlib.h>

int main(int argc, char **argv)
{
	int uid;
	char *dir, **command, *end;
	
	if(argc < 3){
		fprintf(stderr, "Usage - do-chroot dir uid "
                  "command-line...\n");
		exit(1);
	}

	dir = argv[1];
	uid = strtoul(argv[2], &end, 10);
	if(*end != '\0'){
		fprintf(stderr, "the uid \"%s\" isn't a number\n", \
                  argv[2]);
		exit(1);
	}
	command = &argv[3];

	if(chdir(dir) < 0){
		perror("chroot");
		exit(1);
	}

	if(chroot(".") < 0){
		perror("chroot");
		exit(1);
	}

	if(setuid(uid) < 0){
		perror("setuid");
		exit(1);
	}

	execv(command[0], command);
	perror("execv");
	exit(1);
}

Re: [uml-devel] Re: pcap cross-linking [PATCH]

[Blaisorblade]

Forgot to say one thing - the attachment is a minimal chroot-setuid C program 
written by Jeff Dike for his book - it's minimal and trivial to verify.

-- 
Inform me of my mistakes, so I can keep imitating Homer Simpson's "Doh!".
Paolo Giarrusso, aka Blaisorblade (Skype ID "PaoloGiarrusso", ICQ 215621894)
http://www.user-mode-linux.org/~blaisorblade

		
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RE: [uml-devel] Re: pcap cross-linking [PATCH]

[Anthony Brock]

[-- Attachment #1: Type: text/plain, Size: 1637 bytes --]

I don't think the attachment made it into the email. However, I am attaching
one that we've used with good success. It allows us to also specify a "nice"
level for the UML kernel in addition to the chroot-setuid.

Tony


> -----Original Message-----
> From: user-mode-linux-devel-admin@lists.sourceforge.net
> [mailto:user-mode-linux-devel-admin@lists.sourceforge.net]On Behalf Of
> Blaisorblade
> Sent: Wednesday, December 21, 2005 10:13 AM
> To: user-mode-linux-devel@lists.sourceforge.net
> Cc: Rob Landley; Antoine Martin
> Subject: Re: [uml-devel] Re: pcap cross-linking [PATCH]
>
>
> Forgot to say one thing - the attachment is a minimal
> chroot-setuid C program
> written by Jeff Dike for his book - it's minimal and trivial to verify.
>
> --
> Inform me of my mistakes, so I can keep imitating Homer Simpson's "Doh!".
> Paolo Giarrusso, aka Blaisorblade (Skype ID "PaoloGiarrusso", ICQ
> 215621894)
> http://www.user-mode-linux.org/~blaisorblade
>
>
> ___________________________________
> Yahoo! Messenger: chiamate gratuite in tutto il mondo
> http://it.messenger.yahoo.com
>
>
>
> -------------------------------------------------------
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> through log files
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> searching your log files as easy as surfing the  web.  DOWNLOAD SPLUNK!
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> User-mode-linux-devel@lists.sourceforge.net
> https://lists.sourceforge.net/lists/listinfo/user-mode-linux-devel
>

[-- Attachment #2: chrootuidgid.c --]
[-- Type: application/octet-stream, Size: 3560 bytes --]

#include <unistd.h>
#include <pwd.h>
#include <sys/types.h>
#include <sys/param.h>
#include <errno.h>
#include <stdio.h>
#include <stdlib.h>

#define TMP_PATH "/dev/shm"
#define PATH "PATH"
int main(int ac, char **av)
{
	char *param[ac+1];
	char *uname = NULL;
	char *chroot_dir = NULL;
	char *path = NULL;
	struct passwd *userinfo;
	int c, i;
	int nice_val = 0;
	uid_t uid = 0;
	gid_t gid = 0;

	opterr = 0;

	while ((c = getopt(ac, av, "+u:n:p:")) != -1)
		switch (c)
		{
			case 'u':
				uname = optarg;
				break;
			case 'n':
				nice_val = atoi(optarg);
				break;
			case 'p':
				chroot_dir = optarg;
				break;
			case '?':
				if (isprint (optopt))
					fprintf (stderr, "Unknown option `-%c'.\n", optopt);
				else
					fprintf (stderr,
						 "Unknown option character `\\x%x'.\n",
						  optopt);
				return 1;
			default:
				abort();
		}

	if ((uname != NULL) && (chroot_dir != NULL))
	{
		if ((userinfo = getpwnam(uname)) != NULL)
		{
			uid = userinfo->pw_uid;
			gid = userinfo->pw_gid;

			// Adjust the process priority by the requested "nice" value
			if(nice(nice_val) == -1)
			{
				fprintf(stderr, "error changing 'nice' value to %i: %s\n", nice_val, strerror(errno));
				return 1;
			}

			// Abort if we were passed user "root"
			if (uid == 0)
			{
				fprintf (stderr, "Specified account must NOT be root!\n");
				return 1;
			}

			// Clear any existing environment
			path = getenv(PATH);
			if (clearenv())
			{
				fprintf(stderr, "WARNING: unable to clear environment!\n");
			}

			// Setup the command environment
			setenv("HOME", userinfo->pw_dir, 1);
			setenv(PATH, path, 1);
			setenv("TMP", TMP_PATH, 1);
			setenv("USER", userinfo->pw_name, 1);

			// Our first parameter should be the command we're to execute
			// Therefore, we assign this to element '0' of our parameters to pass
			for (i = 0, c = optind; c < ac; i++, c++)
			{
				param[i] = av[c];
			}

			// Abort if we have not other parameters
			if (i == 0)
			{
				fprintf (stderr, "You must specify a command to execute!\n");
				return 1;
			}

			// The final element in the array MUST be a NULL pointer
			param[i] = NULL;

			// First, we need to CHDIR to the CHROOT directory
			if(chdir(chroot_dir) == -1)
			{
				fprintf(stderr, "chdir to '%s' failed: %s\n", chroot_dir, strerror(errno));
				return 3;
			}

			// Next, we need to CHROOT ourselves (while we're still root)
			if(chroot(chroot_dir) == -1)
			{
				fprintf(stderr, "chroot to '%s' failed: %s\n", chroot_dir, strerror(errno));
				return 3;
			}

			// Now CHDIR to the accounts home directory. This is a non-fatal error.
			if(chdir(userinfo->pw_dir) == -1)
			{
				fprintf(stderr, "WARNING: chdir to home directory '%s' failed: %s\n", userinfo->pw_dir, strerror(errno));
			}

			if(setregid(gid, gid) == -1)
			{
				fprintf(stderr, "setregid to gid %i failed: %s\n", gid, strerror(errno));
				return 3;
			}

			if(setreuid(uid, uid) == -1)
			{
				fprintf(stderr, "setreuid to uid %i failed: %s\n", uid, strerror(errno));
				return 3;
			}

			if(execvp(param[0], param) == -1)
			{
				fprintf(stderr, "exec for '%s' failed: %s\n", param[0], strerror(errno));
				return 4;
			}
		}
		else
		{
			fprintf(stderr, "User '%s' not found\n", uname);
			return 2;
		}
	}
	else
	{
		fprintf(stderr, "You must specify a valid account with the '-u' option and a valid chroot path with the '-p' option!\n");
		return 1;
	}
}

Re: [uml-devel] Re: pcap cross-linking [PATCH]

[Blaisorblade]

On Thursday 22 December 2005 18:57, Anthony Brock wrote:
> I don't think the attachment made it into the email.
It was in the previous one but I had forgot to describe it - sorry for the 
misunderstanding.

> However, I am 
> attaching one that we've used with good success. It allows us to also
> specify a "nice" level for the UML kernel in addition to the chroot-setuid.
Nice tool, well written.

Only one minor complaint: you do the following sequence (excluding error 
paths):

	chdir(chroot_dir);
	chroot(chroot_dir);

this will fail needlessly if a relative path is used.

Replacing the chroot with chroot(".") would be better, IMHO.

One question: would 
	chroot(chroot_dir);
	chdir("/");
work equally well?
I've not seen it used so I wonder (a bit) if there can be some hidden bug.
-- 
Inform me of my mistakes, so I can keep imitating Homer Simpson's "Doh!".
Paolo Giarrusso, aka Blaisorblade (Skype ID "PaoloGiarrusso", ICQ 215621894)
http://www.user-mode-linux.org/~blaisorblade

	

	
		
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RE: [uml-devel] Re: pcap cross-linking [PATCH]

[Anthony Brock]

[-- Attachment #1: Type: text/plain, Size: 837 bytes --]

> On Friday December 23, 2005 at 8:11 AM, Blaisorblade wrote:
> Only one minor complaint: you do the following sequence (excluding error
> paths):
>
> 	chdir(chroot_dir);
> 	chroot(chroot_dir);
>
> this will fail needlessly if a relative path is used.

Thanks! This hasn't been an issue since we always use full paths in our
environment. However, it's definitely a bug. I'm attaching a version with
your suggested change.

> Replacing the chroot with chroot(".") would be better, IMHO.
>
> One question: would
> 	chroot(chroot_dir);
> 	chdir("/");
> work equally well?
> I've not seen it used so I wonder (a bit) if there can be some hidden bug.

I'm more comfortable creating a chroot where the "jailed" process never has
an external file reference. However, I don't see why this wouldn't work.
Logically, it should be identical.

Tony

[-- Attachment #2: chrootuidgid.c --]
[-- Type: application/octet-stream, Size: 3553 bytes --]

#include <unistd.h>
#include <pwd.h>
#include <sys/types.h>
#include <sys/param.h>
#include <errno.h>
#include <stdio.h>
#include <stdlib.h>

#define TMP_PATH "/dev/shm"
#define PATH "PATH"
int main(int ac, char **av)
{
	char *param[ac+1];
	char *uname = NULL;
	char *chroot_dir = NULL;
	char *path = NULL;
	struct passwd *userinfo;
	int c, i;
	int nice_val = 0;
	uid_t uid = 0;
	gid_t gid = 0;

	opterr = 0;

	while ((c = getopt(ac, av, "+u:n:p:")) != -1)
		switch (c)
		{
			case 'u':
				uname = optarg;
				break;
			case 'n':
				nice_val = atoi(optarg);
				break;
			case 'p':
				chroot_dir = optarg;
				break;
			case '?':
				if (isprint (optopt))
					fprintf (stderr, "Unknown option `-%c'.\n", optopt);
				else
					fprintf (stderr,
						 "Unknown option character `\\x%x'.\n",
						  optopt);
				return 1;
			default:
				abort();
		}

	if ((uname != NULL) && (chroot_dir != NULL))
	{
		if ((userinfo = getpwnam(uname)) != NULL)
		{
			uid = userinfo->pw_uid;
			gid = userinfo->pw_gid;

			// Adjust the process priority by the requested "nice" value
			if(nice(nice_val) == -1)
			{
				fprintf(stderr, "error changing 'nice' value to %i: %s\n", nice_val, strerror(errno));
				return 1;
			}

			// Abort if we were passed user "root"
			if (uid == 0)
			{
				fprintf (stderr, "Specified account must NOT be root!\n");
				return 1;
			}

			// Clear any existing environment
			path = getenv(PATH);
			if (clearenv())
			{
				fprintf(stderr, "WARNING: unable to clear environment!\n");
			}

			// Setup the command environment
			setenv("HOME", userinfo->pw_dir, 1);
			setenv(PATH, path, 1);
			setenv("TMP", TMP_PATH, 1);
			setenv("USER", userinfo->pw_name, 1);

			// Our first parameter should be the command we're to execute
			// Therefore, we assign this to element '0' of our parameters to pass
			for (i = 0, c = optind; c < ac; i++, c++)
			{
				param[i] = av[c];
			}

			// Abort if we have not other parameters
			if (i == 0)
			{
				fprintf (stderr, "You must specify a command to execute!\n");
				return 1;
			}

			// The final element in the array MUST be a NULL pointer
			param[i] = NULL;

			// First, we need to CHDIR to the CHROOT directory
			if(chdir(chroot_dir) == -1)
			{
				fprintf(stderr, "chdir to '%s' failed: %s\n", chroot_dir, strerror(errno));
				return 3;
			}

			// Next, we need to CHROOT ourselves (while we're still root)
			if(chroot(".") == -1)
			{
				fprintf(stderr, "chroot to '%s' failed: %s\n", chroot_dir, strerror(errno));
				return 3;
			}

			// Now CHDIR to the accounts home directory. This is a non-fatal error.
			if(chdir(userinfo->pw_dir) == -1)
			{
				fprintf(stderr, "WARNING: chdir to home directory '%s' failed: %s\n", userinfo->pw_dir, strerror(errno));
			}

			if(setregid(gid, gid) == -1)
			{
				fprintf(stderr, "setregid to gid %i failed: %s\n", gid, strerror(errno));
				return 3;
			}

			if(setreuid(uid, uid) == -1)
			{
				fprintf(stderr, "setreuid to uid %i failed: %s\n", uid, strerror(errno));
				return 3;
			}

			if(execvp(param[0], param) == -1)
			{
				fprintf(stderr, "exec for '%s' failed: %s\n", param[0], strerror(errno));
				return 4;
			}
		}
		else
		{
			fprintf(stderr, "User '%s' not found\n", uname);
			return 2;
		}
	}
	else
	{
		fprintf(stderr, "You must specify a valid account with the '-u' option and a valid chroot path with the '-p' option!\n");
		return 1;
	}
}

Re: [uml-devel] Re: pcap cross-linking [PATCH]

[Rob Landley]

On Friday 23 December 2005 10:11, Blaisorblade wrote:
> One question: would
>  chroot(chroot_dir);
>  chdir("/");
> work equally well?
> I've not seen it used so I wonder (a bit) if there can be some hidden bug.

http://www.ussg.iu.edu/hypermail/linux/kernel/0511.2/0185.html

Rob
-- 
Steve Ballmer: Innovation!  Inigo Montoya: You keep using that word.
I do not think it means what you think it means.


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Re: [uml-devel] Re: pcap cross-linking [PATCH]

[Blaisorblade]

On Thursday 29 December 2005 21:12, Rob Landley wrote:
> On Friday 23 December 2005 10:11, Blaisorblade wrote:
> > One question: would
> >  chroot(chroot_dir);
> >  chdir("/");
> > work equally well?
> > I've not seen it used so I wonder (a bit) if there can be some hidden
> > bug.
>
> http://www.ussg.iu.edu/hypermail/linux/kernel/0511.2/0185.html

So? I've read this message, but my (original) main question was:
is 
> >  chroot(chroot_dir);
> >  chdir("/");
the same as 
> >  chdir(chroot_dir);
> >  chroot(".");
?

Maybe there was a misunderstanding, but the answer to the question is still 
"it seems yes, until somebody shows me I'm wrong".

I know that yes, chroot() has all the other problems (like the "root can 
escape" described in man 2 chroot, or the one by Linus).

-- 
Inform me of my mistakes, so I can keep imitating Homer Simpson's "Doh!".
Paolo Giarrusso, aka Blaisorblade (Skype ID "PaoloGiarrusso", ICQ 215621894)
http://www.user-mode-linux.org/~blaisorblade

		
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Re: [uml-devel] Re: pcap cross-linking [PATCH]

[Rob Landley]

On Sunday 01 January 2006 12:51, Blaisorblade wrote:

> So? I've read this message, but my (original) main question was:
> is
>
> > >  chroot(chroot_dir);
> > >  chdir("/");
>
> the same as
>
> > >  chdir(chroot_dir);
> > >  chroot(".");
>
> ?

All chroot does is change the / value.  It doesn't recalculate .. for the 
current directory, so if you don't chdir after the chroot you may wind up 
with .. pointing someplace it shouldn't. 

Rob
-- 
Steve Ballmer: Innovation!  Inigo Montoya: You keep using that word.
I do not think it means what you think it means.


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Re: [uml-devel] Re: pcap cross-linking [PATCH]

[Blaisorblade]

On Sunday 01 January 2006 22:01, Rob Landley wrote:
> On Sunday 01 January 2006 12:51, Blaisorblade wrote:
> > So? I've read this message, but my (original) main question was:
> > is
> >
> > > >  chroot(chroot_dir);
> > > >  chdir("/");
> >
> > the same as
> >
> > > >  chdir(chroot_dir);
> > > >  chroot(".");
> >
> > ?
>
> All chroot does is change the / value.  It doesn't recalculate .. for the
> current directory, so if you don't chdir after the chroot you may wind up
> with .. pointing someplace it shouldn't.
I know that, but in fact I included chdir("/") after the chroot.
-- 
Inform me of my mistakes, so I can keep imitating Homer Simpson's "Doh!".
Paolo Giarrusso, aka Blaisorblade (Skype ID "PaoloGiarrusso", ICQ 215621894)
http://www.user-mode-linux.org/~blaisorblade

	

	
		
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Re: [uml-devel] Re: pcap cross-linking

[Blaisorblade]

On Monday 19 December 2005 17:16, Blaisorblade wrote:
> On Sunday 18 December 2005 20:03, Antoine Martin wrote:
> > Paolo,
> >
> > pcap builds and runs fine on amd64 but there is a problem when building
> > with SUBARCH=i386: it uses the wrong version of libpcap.a:
> > ld -r -dp -o arch/um/drivers/pcap.o arch/um/drivers/pcap_kern.o
> > arch/um/drivers/pcap_user.o  -m elf_i386
> > -r /usr/lib/gcc/x86_64-pc-linux-gnu/3.4.4/../../../libpcap.a
> >
> > Whereas the one it needs to link against is here:
> > /emul/linux/x86/usr/lib/libpcap.a
>
> This is IMHO a Gentoo bug - it is not setup for compilation of 32-bit
> binaries using anything else than glibc. I hit this problem with
> libncurses, when doing make menuconfig ARCH=um (now this was solved as
> helper programs are built as native again).

> However, I built uml with libpcap by default for some time - possibly it
> was before me switching to 64-bit linux.

No, the thing works but only because I indeed symlinked 32-bit libraries 
inside /usr/lib32.
-- 
Inform me of my mistakes, so I can keep imitating Homer Simpson's "Doh!".
Paolo Giarrusso, aka Blaisorblade (Skype ID "PaoloGiarrusso", ICQ 215621894)
http://www.user-mode-linux.org/~blaisorblade

		
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