Re: problems with latest smbfs changes on 2.4.34 and security backports

[Santiago Garcia Mantinan <manty@debian.org>]

Hi again!

I tried to replicate the problem at home during the weekend with my laptop,
but I couldn't get it to show links with previous kernels, so I guess I had
something different on my samba server or similar, I'm at the real machines
now so I have done the real tests and they look promising. I'm getting
completely different results than those of Grant, which seems really weird.

I applied just this patch:

> > >--- kernel-source-2.4.27.orig/fs/smbfs/proc.c	2007-01-19 17:53:57.247695476 -0700
> > >+++ kernel-source-2.4.27/fs/smbfs/proc.c	2007-01-19 17:49:07.480161733 -0700
> > >@@ -1997,7 +1997,7 @@
> > > 		fattr->f_mode = (server->mnt->dir_mode & (S_IRWXU | S_IRWXG | S_IRWXO)) | S_IFDIR;
> > > 	else if ( (server->mnt->flags & SMB_MOUNT_FMODE) &&
> > > 	          !(S_ISDIR(fattr->f_mode)) )
> > >-		fattr->f_mode = (server->mnt->file_mode & (S_IRWXU | S_IRWXG | S_IRWXO)) | S_IFREG;
> > >+		fattr->f_mode = (server->mnt->file_mode & (S_IRWXU | S_IRWXG | S_IRWXO)) | (fattr->f_mode & S_IFMT);
> > > 
> > > }

To an unpatched 2.4.34, the client is an IBM NetworkStation 1000 (a PowerPC
based thin client), and the server is a normal amd64 based PC running
2.6.19.1, both running Debian, the client runs Sarge and the Server Etch.
I'm descriving this to see if differences on the architectures could be
causing the differences on behaviour between my tests and Grant's.

> > client running 2.4.34 with above patch, server is running 2.6.19.2 to 
> > eliminate it from the problem space (hopefully ;) :
> > grant@sempro:/home/other$ uname -r
> > 2.4.34b
> > grant@sempro:/home/other$ ls -l
> > total 9
> > drwxr-xr-x 1 grant wheel 4096 2007-01-21 11:44 dir/
> > drwxr-xr-x 1 grant wheel 4096 2007-01-21 11:44 dirlink/
> > -rwxr-xr-x 1 grant wheel   15 2007-01-21 11:43 file*
> > -rwxr-xr-x 1 grant wheel   15 2007-01-21 11:43 filelink*
> 
> It seems to me that there is a difference, because filelink now appears the
> same size as file. It's just as if we had hard links instead of symlinks.

Here is what I did, I mounted the remote filesystem on /mnt on my client,
the share on the server has a normal Debian Sarge PowerPC filesystem on it.

$ pwd
/mnt/usr
$ ls -l
total 0
drwxr-xr-x  1 root root  0 Feb 15  2005 X11R6
drwxr-xr-x  1 root root  0 Jan 16  2007 bin
drwxr-xr-x  1 root root  0 Jan 16  2007 doc
drwxr-xr-x  1 root root  0 Feb 10  2005 games
drwxr-xr-x  1 root root  0 Jan 16  2007 include
lrwxr-xr-x  1 root root 10 Jan 16  2007 info -> share/info
drwxr-xr-x  1 root root  0 Jan 16  2007 lib
drwxr-xr-x  1 root root  0 Feb 10  2005 local
drwxr-xr-x  1 root root  0 Jan 16  2007 sbin
drwxr-xr-x  1 root root  0 Jan  5  2006 share
drwxr-xr-x  1 root root  0 Dec 15  2004 src
$ ls -l info/
total 249856
-rwxr-xr-x  1 root root 150109 Jul 16  2004 coreutils.info.gz
-rwxr-xr-x  1 root root   1299 Jan 16  2007 dir
-rwxr-xr-x  1 root root   1299 Jan 16  2007 dir.old
-rwxr-xr-x  1 root root  28019 Mar 20  2005 find.info.gz
-rwxr-xr-x  1 root root  26136 Nov 22  2004 grep.info.gz
-rwxr-xr-x  1 root root  12914 Sep 16  2006 gzip.info.gz
-rwxr-xr-x  1 root root  12316 Sep 18  2005 ipc.info.gz
-rwxr-xr-x  1 root root  21432 Jan 23  2005 rl5userman.info.gz
-rwxr-xr-x  1 root root  26647 Dec  1  2004 sed.info.gz
-rwxr-xr-x  1 root root 123382 Dec  1  2006 tar.info.gz
-rwxr-xr-x  1 root root  54876 May 23  2005 wget.info.gz
$ cd ../bin
$ ls -l sh
lrwxr-xr-x  1 root root 4 Jan 16  2007 sh -> bash
$ dd if=sh bs=1 count=6
ELF
6+0 records in
6+0 records out
6 bytes transferred in 0.001432 seconds (4190 bytes/sec)

As you can see I now can see the symbolic links perfectly and they work as
expected.

In fact, this patch is working so well that it poses a security risk, as now
the devices on my /mnt/dev directory are not only seen as devices (like they
were seen on 2.4.33) but they also work (which didn't happen on 2.4.33).

So... for me now the remote filesystem works as if it was a local
filesystem, without any difference of behaviour, not even on special files
like devices or whatever.

As I said before... this behaviour of having the remote device files work...
seems a security problem and I don't think is desirable, other than that it
seems to work well on my PowerPC, I'll try to run the tests on a normal x86
client and report back.

Regards...
-- 
Santiago García Mantiñán
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