On Sun, Sep 14, 2014 at 10:15:10PM +0900, Seunghun Lee wrote:

It would make more sense to pass char __user * instead of
char * in callers of do_mount() and do getname() inside do_mount().

Suggested-by: Al Viro <viro@ZenIV.linux.org.uk>
Signed-off-by: Seunghun Lee <redacted>

Applied with one modification: this getname/kern_path/putname is equivalent to
user_path(dir_name, &path) and do_mount() becomes simpler if we use that
instead of not-quite-opencoding it.

Beginning of do_mount() becomes simply
        /* Discard magic */
        if ((flags & MS_MGC_MSK) == MS_MGC_VAL)
                flags &= ~MS_MGC_MSK;

        /* Basic sanity checks */
        if (data_page)
                ((char *)data_page)[PAGE_SIZE - 1] = 0;

        /* ... and get the mountpoint */
        retval = user_path(dir_name, &path);
        if (retval)
                return retval;
that way, and there's no struct filename * to discard on exit; getname and
putname are done inside user_path().