linux-kernel - Re: [patch] unprivileged mounts update

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Message-ID: <20070426145733.GA10078@sergelap.austin.ibm.com>
Date:	Thu, 26 Apr 2007 09:57:33 -0500
From:	"Serge E. Hallyn" <serue@...ibm.com>
To:	Miklos Szeredi <miklos@...redi.hu>
Cc:	serge@...lyn.com, hpa@...or.com, linuxram@...ibm.com,
	linux-kernel@...r.kernel.org, containers@...ts.osdl.org,
	linux-security-module@...r.kernel.org, ebiederm@...ssion.com,
	viro@....linux.org.uk, linux-fsdevel@...r.kernel.org,
	akpm@...ux-foundation.org
Subject: Re: [patch] unprivileged mounts update

Quoting Miklos Szeredi (miklos@...redi.hu):
> > Right, I figure if the normal action is to always do
> > mnt->user = current->fsuid, then for the special case we
> > pass a uid in someplace.  Of course...  do we not have a
> > place to do that?  Would it be a no-no to use 'data' for
> > a non-fs-specific arg?
> 
> I guess it would be OK for bind, but not for new- and remounts, where
> 'data' is already used.
> 
> Maybe it's best to stay with fsuid after all, and live with having to
> restore capabilities.  It's not so bad after all, this seems to do the
> trick:
> 
> 	cap_t cap = cap_get_proc();
> 	setfsuid(uid);
> 	cap_set_proc(cap);
> 
> Unfortunately these functions are not in libc, but in a separate
> "libcap" library.  Ugh.

Ok, are you still planning to nix the MS_SETUSER flag, though, as Eric
suggested?  I think it's cleanest - always set the mnt->user field to
current->fsuid, and require CAP_SYS_ADMIN if the mountpoint->mnt->user !=
current->fsuid.

-serge
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