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    SubjectRe: [PATCH v2] vfs: add NOFOLLOW flag to umount(2)
    On Sun, 21 Feb 2010, Al Viro wrote:
    > On Thu, Feb 11, 2010 at 12:21:00PM -0500, Christoph Hellwig wrote:
    > > On Wed, Feb 10, 2010 at 12:15:53PM +0100, Miklos Szeredi wrote:
    > > > - renamed flag to UMOUNT_NOFOLLOW
    > > > - added UMOUNT_UNUSED for feature detection
    > >
    > > Umm, why? MNT_ certainly isn't the best naming for unmount flags,
    > > but switching convention after we had a few doesn't make any sense.
    > Actually, I've got more interesting question: what's being attempted
    > there? Is that just a "let's protect ourselves against somebody feeding
    > us an untrusted symlink"? I'm not sure if it makes much sense; if we
    > are dealing with pathnames on untrusted fs, there's nothing to stop the
    > attacker from having /mnt/foo/dir (originally containing a mountpoint
    > at /mnt/foo/dir/usr) killed and replaced with a symlink to /, making any
    > code that does umount() on such pathnames vulnerable as hell anyway.

    It is trivial to check the path up to the mountpoint (chdir + getcwd).
    But doing that on the mountpoint will make it busy, so NOFOLLOW is
    really needed there.


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      Last update: 2010-02-22 21:33    [W:0.019 / U:3.400 seconds]
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