[uml-devel] hostfs permissions

[uml-devel] hostfs permissions

[Karl Chen]

Hi, I'm doing some large-scale security experiments on Debian
security.  I'm using UML to do the whole thing on a cluster.

Hostfs seems to make everything owned by root -- even files
created by non-root users.  I'm currently using 2.4.26-3 (Debian
package).  I found a few posts via Google mentioning a patch to
fix this, but no other information.  What is the modified behavior
of hostfs permissions?  Has this been integrated into a newer
version, or is it in cvs, or if not, are there plans to?

[I think the ideal behavior, if UML is running as non-root, would
be if there were a temporary mapping of ownership (e.g. so chown
works) -- but that would be a lot of work to implement.]

I would be happy if there were uid and gid mount options as many
other fs types have -- to treat all files in the entire mount as
owned by a particular user/group.

-- 
Karl 2005-06-09 22:10


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Re: [uml-devel] hostfs permissions

[Blaisorblade]

On Friday 10 June 2005 07:34, Karl Chen wrote:
> Hi, I'm doing some large-scale security experiments on Debian
> security.  I'm using UML to do the whole thing on a cluster.

> Hostfs seems to make everything owned by root -- even files
> created by non-root users.
So you are running uml as root?

Or you are running UML as non-root but with hostfs as root filesystem? In this 
case you're possibly seeing the result of a trick made to make it work 
well... but I don't know if that trick is present in the UML version you're 
using.

> I'm currently using 2.4.26-3 (Debian 
> package).
Hmm, in that case
> I found a few posts via Google mentioning a patch to 
> fix this, but no other information.  What is the modified behavior
> of hostfs permissions?  Has this been integrated into a newer
> version, or is it in cvs, or if not, are there plans to?
Well, there are:
1) HUMFS, implementing the ideal behaviour below
2) a patch posted by somebody for when UML is run by root, to allow created 
files to get the UID of the process creating it inside UML.

> [I think the ideal behavior, if UML is running as non-root, would
> be if there were a temporary mapping of ownership (e.g. so chown
> works) -- but that would be a lot of work to implement.]
Well, this work has been started but is currently stalled because of other 
ongoing work, however I hope we'll resurrect that shortly.
> I would be happy if there were uid and gid mount options as many
> other fs types have -- to treat all files in the entire mount as
> owned by a particular user/group.

Well, I'm going to add those options to UML 2.6 but I'll be able to work on 
this only next week... However this should not be too much work.
-- 
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] hostfs permissions

[Karl Chen]

>>>>> On 2005-06-10 09:03 PDT, Blaisorblade  writes:
    >> Hostfs seems to make everything owned by root -- even files
    >> created by non-root users.
    Blaisorblade> So you are running uml as root?

    Blaisorblade> Or you are running UML as non-root but with
    Blaisorblade> hostfs as root filesystem? 

I'm running uml as non-root (that's part of the reason for using
UML, so I can do everything as non-root), and not using hostfs as
the root file system.  I just need to share one directory tree,
and some processes inside the uml need to run as non-root.

    Blaisorblade> 1) HUMFS, implementing the ideal behaviour below

Humfs looks promising; I'm investigating - thanks.

    >> I would be happy if there were uid and gid mount options as
    >> many other fs types have -- to treat all files in the
    >> entire mount as owned by a particular user/group.

    Blaisorblade> Well, I'm going to add those options to UML 2.6
    Blaisorblade> but I'll be able to work on this only next
    Blaisorblade> week... However this should not be too much
    Blaisorblade> work.

Great! Thanks!  Let me know if I can help with anything.

-- 
Karl 2005-06-10 13:06


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Re: [uml-devel] hostfs permissions

[Blaisorblade]

On Friday 10 June 2005 22:14, Karl Chen wrote:
> >>>>> On 2005-06-10 09:03 PDT, Blaisorblade  writes:
>     >> Hostfs seems to make everything owned by root -- even files
>     >> created by non-root users.
>
>     Blaisorblade> So you are running uml as root?
>
>     Blaisorblade> Or you are running UML as non-root but with
>     Blaisorblade> hostfs as root filesystem?
>
> I'm running uml as non-root (that's part of the reason for using
> UML, so I can do everything as non-root), and not using hostfs as
> the root file system.  I just need to share one directory tree,
> and some processes inside the uml need to run as non-root.
Ok, in this case there's probably a simpler road: simply use a 2.4.27-1bs 
kernel. The implemented behaviour is that all created files will have the ID 
they have on the host, i.e. the ID of the user running UML.
>     Blaisorblade> 1) HUMFS, implementing the ideal behaviour below
>
> Humfs looks promising; I'm investigating - thanks.

>     >> I would be happy if there were uid and gid mount options as
>     >> many other fs types have -- to treat all files in the
>     >> entire mount as owned by a particular user/group.
>
>     Blaisorblade> Well, I'm going to add those options to UML 2.6
>     Blaisorblade> but I'll be able to work on this only next
>     Blaisorblade> week... However this should not be too much
>     Blaisorblade> work.
>
> Great! Thanks!  Let me know if I can help with anything.

-- 
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] hostfs permissions

[Karl Chen]

>>>>> On 2005-06-10 15:26 PDT, Blaisorblade  writes:

    Blaisorblade> Ok, in this case there's probably a simpler
    Blaisorblade> road: simply use a 2.4.27-1bs kernel. The
    Blaisorblade> implemented behaviour is that all created files
    Blaisorblade> will have the ID they have on the host, i.e. the
    Blaisorblade> ID of the user running UML.

Thanks for the tip!  I will be running UML under different user
IDs but I'd rather it always be the same uid inside the UML.  I
used this micropatch to get exactly the behavior I want.  It's
obviously for this particular experiment only; I still think
uid,gid mount options would be better in general.  I guess that's
only 5 or 10 more lines of code...


diff -u /home/quarl/proj/uml/linux/linux-2.4.27/arch/um/fs/hostfs/.backup/hostfs_kern.c.\~1\~ /home/quarl/proj/uml/linux/linux-2.4.27/arch/um/fs/hostfs/hostfs_kern.c
--- /home/quarl/proj/uml/linux/linux-2.4.27/arch/um/fs/hostfs/.backup/hostfs_kern.c.~1~	2005-06-10 16:58:51.000000000 -0700
+++ /home/quarl/proj/uml/linux/linux-2.4.27/arch/um/fs/hostfs/hostfs_kern.c	2005-06-10 17:35:01.829485585 -0700
@@ -1,3 +1,6 @@
+#define KLUDGE_FS_UID 7777
+#define KLUDGE_FS_GID 7777
+
 /*
  * Copyright (C) 2000 - 2003 Jeff Dike (jdike@addtoit.com)
  * Licensed under the GPL
@@ -142,6 +145,10 @@
 	ino->i_blocks = i_blocks;
 	if(kdev_same(ino->i_sb->s_dev, ROOT_DEV) && (ino->i_uid == getuid()))
 		ino->i_uid = 0;
+        else if (ino->i_uid == getuid()) {          /* KC KLUDGE */
+                ino->i_uid = KLUDGE_FS_UID;         /* KC KLUDGE */
+                ino->i_gid = KLUDGE_FS_GID;         /* KC KLUDGE */
+        }                                           /* KC KLUDGE */
 	return(0);
 }
 
@@ -760,13 +767,17 @@
 		if(kdev_same(dentry->d_inode->i_sb->s_dev, ROOT_DEV) &&
 		   (attr->ia_uid == 0))
 			attr->ia_uid = getuid();
+                else if (attr->ia_uid == KLUDGE_FS_UID) { /* KC KLUDGE */
+                        attr->ia_uid = getuid();          /* KC KLUDGE */
+                        attr->ia_gid = getgid();          /* KC KLUDGE */
+                }                                         /* KC KLUDGE */
 		attrs.ia_valid |= HOSTFS_ATTR_UID;
 		attrs.ia_uid = attr->ia_uid;
 	}
 	if(attr->ia_valid & ATTR_GID){
 		if(kdev_same(dentry->d_inode->i_sb->s_dev, ROOT_DEV) &&
 		   (attr->ia_gid == 0))
-			attr->ia_gid = getuid();
+			attr->ia_gid = getgid();
 		attrs.ia_valid |= HOSTFS_ATTR_GID;
 		attrs.ia_gid = attr->ia_gid;
 	}


-- 
Karl 2005-06-10 17:44


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Re: [uml-devel] hostfs permissions

[Blaisorblade]

On Saturday 11 June 2005 02:48, Karl Chen wrote:
> >>>>> On 2005-06-10 15:26 PDT, Blaisorblade  writes:
>
>     Blaisorblade> Ok, in this case there's probably a simpler
>     Blaisorblade> road: simply use a 2.4.27-1bs kernel. The
>     Blaisorblade> implemented behaviour is that all created files
>     Blaisorblade> will have the ID they have on the host, i.e. the
>     Blaisorblade> ID of the user running UML.
>
> Thanks for the tip!  I will be running UML under different user
> IDs but I'd rather it always be the same uid inside the UML.  I
> used this micropatch to get exactly the behavior I want. It's
> obviously for this particular experiment only; I still think
> uid,gid mount options would be better in general.  I guess that's
> only 5 or 10 more lines of code...
Yes, I just need a bit of time to implement all cases and especially option 
parsing. And I can confirm your micropatch does exactly the work you need.

> diff -u
> /home/quarl/proj/uml/linux/linux-2.4.27/arch/um/fs/hostfs/.backup/hostfs_ke
>rn.c.\~1\~
> /home/quarl/proj/uml/linux/linux-2.4.27/arch/um/fs/hostfs/hostfs_kern.c ---
> /home/quarl/proj/uml/linux/linux-2.4.27/arch/um/fs/hostfs/.backup/hostfs_ke
>rn.c.~1~	2005-06-10 16:58:51.000000000 -0700 +++
> /home/quarl/proj/uml/linux/linux-2.4.27/arch/um/fs/hostfs/hostfs_kern.c	200
>5-06-10 17:35:01.829485585 -0700 @@ -1,3 +1,6 @@
> +#define KLUDGE_FS_UID 7777
> +#define KLUDGE_FS_GID 7777
> +
>  /*
>   * Copyright (C) 2000 - 2003 Jeff Dike (jdike@addtoit.com)
>   * Licensed under the GPL
> @@ -142,6 +145,10 @@
>  	ino->i_blocks = i_blocks;
>  	if(kdev_same(ino->i_sb->s_dev, ROOT_DEV) && (ino->i_uid == getuid()))
>  		ino->i_uid = 0;
> +        else if (ino->i_uid == getuid()) {          /* KC KLUDGE */
> +                ino->i_uid = KLUDGE_FS_UID;         /* KC KLUDGE */
> +                ino->i_gid = KLUDGE_FS_GID;         /* KC KLUDGE */
> +        }                                           /* KC KLUDGE */
>  	return(0);
>  }
>
> @@ -760,13 +767,17 @@
>  		if(kdev_same(dentry->d_inode->i_sb->s_dev, ROOT_DEV) &&
>  		   (attr->ia_uid == 0))
>  			attr->ia_uid = getuid();
> +                else if (attr->ia_uid == KLUDGE_FS_UID) { /* KC KLUDGE */
> +                        attr->ia_uid = getuid();          /* KC KLUDGE */
> +                        attr->ia_gid = getgid();          /* KC KLUDGE */
> +                }                                         /* KC KLUDGE */
>  		attrs.ia_valid |= HOSTFS_ATTR_UID;
>  		attrs.ia_uid = attr->ia_uid;
>  	}
>  	if(attr->ia_valid & ATTR_GID){
>  		if(kdev_same(dentry->d_inode->i_sb->s_dev, ROOT_DEV) &&
>  		   (attr->ia_gid == 0))
> -			attr->ia_gid = getuid();
> +			attr->ia_gid = getgid();
>  		attrs.ia_valid |= HOSTFS_ATTR_GID;
>  		attrs.ia_gid = attr->ia_gid;
>  	}

-- 
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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