Re: About /etc/mtab and /proc/mounts

Kasper Dupont (
Sun, 02 Mar 2003 15:16:21 +0100

DervishD wrote:
> If 'mount' treats specially the
> mtab if it is a symlink... well, IMHO this is not correct. Yes, this
> can lead to an attack, but: 'mount' is a setuid program, and only
> root can symlink /etc/mtab, true?

The reason for mount not to update /etc/mtab if it is a symlink is
not security concerns, but rather that it could be a symlink to
/proc/mounts. Another problem is the way the update is actually
done. A lockfile named /etc/mtab~ is created, and a new mtab is
written to /etc/mtab.tmp which is later renamed on top of mtab.

Some of this can obviously be solved by changing mount. But if we
are going to change mount in non-trivial ways, we should aim for a
better longterm solution. It would be possible for mount to start
from /et/mtab and use readlink until the actual location is found.
Then if the path starts with /proc/ the update can be skipped, or
done in a different way. And if the location is outside /proc then
create lockfilename and tempfilename by appending to this path.

But all that is IMHO a bad solution. Getting the actual location
right is nontrivial. And we should rather aim for an implementation
in /proc and have mount write there directly. But there are a few
open questions I'd like answered before trying to implement a

Kasper Dupont -- der bruger for meget tid på usenet.
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