Re: [PATCH] add some long-missing capabilities to fs_mask

["Serge E. Hallyn" <serue@us.ibm.com>]

Quoting Valdis.Kletnieks@vt.edu (Valdis.Kletnieks@vt.edu):
> On Mon, 13 Apr 2009 09:56:14 CDT, "Serge E. Hallyn" said:
> > When POSIX capabilities were introduced during the 2.1 Linux
> > cycle, the fs mask, which represents the capabilities which having
> > fsuid==0 is supposed to grant, did not include CAP_MKNOD and
> > CAP_LINUX_IMMUTABLE.  However, before capabilities the privilege
> > to call these did in fact depend upon fsuid==0.
> 
> Wow. How did this manage to stay un-noticed for this long?

I guess setfsuid() is mainly used by NFS, and not a lot of people
do mknod over NFS?

To run into this, you'd have to do something like

	1. run as root
	2. setresuid(500,500,0);
	3. (...)
	4. setfsuid(0);
	5. mknod(path, mode, dev);

so I suspect the simpler (cross-platform) thing to do was
seteuid(0) for the mknod anyway...  Plus there is nowhere I've
found where the precise capabilities afforded to fsuid=0 are
documented, so noone would complain, they'd just accept it and
do seteuid()?

I'm guessing of course.

-serge