On Wed, Sep 04, 2013 at 03:05:23PM -0400, Waiman Long wrote:
>
> static int prepend_name(char **buffer, int *buflen, struct qstr *name)
> {
> - return prepend(buffer, buflen, name->name, name->len);
> + /*
> + * With RCU path tracing, it may race with rename. Use
> + * ACCESS_ONCE() to make sure that it is either the old or
> + * the new name pointer. The length does not really matter as
> + * the sequence number check will eventually catch any ongoing
> + * rename operation.
> + */
> + const char *dname = ACCESS_ONCE(name->name);
> + int dlen = name->len;
> +
> + if (unlikely(!dname || !dlen))
> + return -EINVAL;
> + return prepend(buffer, buflen, dname, dlen);
NAK. A race with d_move() can very well leave you with dname pointing into
an object of length smaller than dlen. You *can* copy it byte-by-byte
and rely on NUL-termination, but you can't rely on length being accurate -
not without having excluded d_move().
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