Re: [patch] unprivileged mounts update
- From: "Serge E. Hallyn" <serue@xxxxxxxxxx>
- Date: Wed, 25 Apr 2007 12:20:12 -0500
Quoting H. Peter Anvin (hpa@xxxxxxxxx):
Miklos Szeredi wrote:
Andrew, please skip this patch, for now.
Serge found a problem with the fsuid approach: setfsuid(nonzero) will
remove filesystem related capabilities. So even if root is trying to
set the "user=UID" flag on a mount, access to the target (and in case
of bind, the source) is checked with user privileges.
Root should be able to set this flag on any mountpoint, _regardless_
of permissions.
Right, if you're using fsuid != 0, you're not running as root
Sure, but what I'm not clear on is why, if I've done a
prctl(PR_SET_KEEPCAPS, 1) before the setfsuid, I still lose the
CAP_FS_MASK perms. I see the special case handling in
cap_task_post_setuid(). I'm sure there was a reason for it, but
this is a piece of the capability implementation I don't understand
right now.
I would send in a patch to make it honor current->keep_capabilities,
but I have a feeling there was a good reason not to do so in the
first place.
(fsuid is
the equivalent to euid for the filesystem.)
If it were really the equivalent then I could keep my capabilities :)
after changing it.
I fail to see how ruid should have *any* impact on mount(2). That seems
to be a design flaw.
May be, but just using fsuid at this point stops me from enabling user
mounts under /share if /share is chmod 000 (which it is).
thanks,
-serge
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