Messages in this thread | | | Date | Thu, 17 Sep 2015 07:30:34 -0400 | From | Tejun Heo <> | Subject | Re: Possible netlink autobind regression |
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Hello, Herbert.
On Thu, Sep 17, 2015 at 01:15:03PM +0800, Herbert Xu wrote: > netlink: Fix autobind race condition that leads to zero port ID > > The commit c0bb07df7d981e4091432754e30c9c720e2c0c78 ("netlink: > Reset portid after netlink_insert failure") introduced a race > condition where if two threads tried to autobind the same socket > one of them may end up with a zero port ID. > > This patch reverts that commit and instead fixes it by introducing > a separte "bound" variable to indicate whether a user-space socket > has been bound. > > Fixes: c0bb07df7d98 ("netlink: Reset portid after netlink_insert failure") > Reported-by: Tejun Heo <tj@kernel.org> > Reported-by: Linus Torvalds <torvalds@linux-foundation.org> > Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au> > Reviewed-by: Cong Wang <cwang@twopensource.com>
Maybe add that this led to a deadlock and add a Link tag to this thread?
> @@ -1083,10 +1083,12 @@ static int netlink_insert(struct sock *sk, u32 portid) > if (err) { > if (err == -EEXIST) > err = -EADDRINUSE; > - nlk_sk(sk)->portid = 0; > sock_put(sk); > + goto err; > } > > + nlk_sk(sk)->bound = !!portid;
!! isn't necessasry and this creates ordering between two stores. ->bound must be visible only after ->portid is visible, so this should be smp_store_release().
> @@ -2371,7 +2373,7 @@ static int netlink_sendmsg(struct socket *sock, struct msghdr *msg, size_t len) > dst_group = nlk->dst_group; > } > > - if (!nlk->portid) { > + if (!nlk->bound) {
And all unlocked reads should be smp_load_acquire().
> err = netlink_autobind(sock); > if (err) > goto out;
Thanks.
-- tejun
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