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SubjectRe: [held lock freed] Re: [GIT] Networking

* Arnd Bergmann <arnd@arndb.de> wrote:

> On Monday 21 March 2011, Eric Dumazet wrote:
> > > diff --git a/net/x25/af_x25.c b/net/x25/af_x25.c
> > > index 4680b1e..b2cf1db 100644
> > > --- a/net/x25/af_x25.c
> > > +++ b/net/x25/af_x25.c
> > > @@ -669,8 +669,8 @@ static int x25_release(struct socket *sock)
> > >
> > > sock_orphan(sk);
> > > out:
> > > - release_sock(sk);
> > > sock_put(sk);
> > > + release_sock(sk);
> > > return 0;
> > > }
> > >
> >
> > Hmm, x25_release() looks fine, I believe no fix is needed.
> >
>
> D'oh. You're right of course. My patch would introduce the bug,
> not fix it. Updated patch below.
>
> Arnd
> 8<-------------------------
> net/appletalk: fix atalk_release use after free
>
> The BKL removal in appletalk introduced a use-after-free problem,
> where atalk_destroy_socket frees a sock, but we still release
> the socket lock on it.
>
> An easy fix is to take an extra reference on the sock and sock_put
> it when returning from atalk_release.
>
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
>
> index 3d4f4b0..206e771 100644
> --- a/net/appletalk/ddp.c
> +++ b/net/appletalk/ddp.c
> @@ -1051,6 +1051,7 @@ static int atalk_release(struct socket *sock)
> {
> struct sock *sk = sock->sk;
>
> + sock_hold(sk);
> lock_sock(sk);
> if (sk) {
> sock_orphan(sk);
> @@ -1058,6 +1059,8 @@ static int atalk_release(struct socket *sock)
> atalk_destroy_socket(sk);
> }
> release_sock(sk);
> + sock_put(sk);
> +
> return 0;
> }

I have not triggered the lockdep warning in this code yet - but i've ran the
patch and have seen no ill effects from it so far.

Thanks,

Ingo


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