netdev - Re: [PATCH v2 bpf 1/2] bpf, sockmap: fix potential msg memory leak

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Date:   Mon, 05 Jul 2021 09:27:49 -0700
From:   John Fastabend <john.fastabend@...il.com>
To:     Cong Wang <xiyou.wangcong@...il.com>,
        John Fastabend <john.fastabend@...il.com>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andriin@...com>, bpf <bpf@...r.kernel.org>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>
Subject: Re: [PATCH v2 bpf 1/2] bpf, sockmap: fix potential msg memory leak

Cong Wang wrote:
> On Thu, Jul 1, 2021 at 5:12 PM John Fastabend <john.fastabend@...il.com> wrote:
> >
> > If skb_linearize is needed and fails we could leak a msg on the error
> > handling. To fix ensure we kfree the msg block before returning error.
> > Found during code review.
> >
> > Fixes: 4363023d2668e ("bpf, sockmap: Avoid failures from skb_to_sgvec when skb has frag_list")
> > Signed-off-by: John Fastabend <john.fastabend@...il.com>
> > ---
> >  net/core/skmsg.c | 4 +++-
> >  1 file changed, 3 insertions(+), 1 deletion(-)
> >
> > diff --git a/net/core/skmsg.c b/net/core/skmsg.c
> > index 9b6160a191f8..22603289c2b2 100644
> > --- a/net/core/skmsg.c
> > +++ b/net/core/skmsg.c
> > @@ -505,8 +505,10 @@ static int sk_psock_skb_ingress_enqueue(struct sk_buff *skb,
> >          * drop the skb. We need to linearize the skb so that the mapping
> >          * in skb_to_sgvec can not error.
> >          */
> > -       if (skb_linearize(skb))
> > +       if (skb_linearize(skb)) {
> > +               kfree(msg);
> >                 return -EAGAIN;
> > +       }
> >         num_sge = skb_to_sgvec(skb, msg->sg.data, 0, skb->len);
> >         if (unlikely(num_sge < 0)) {
> >                 kfree(msg);
> 
> I think it is better to let whoever allocates msg free it, IOW,
> let sk_psock_skb_ingress_enqueue()'s callers handle its failure.

Sure, although we already have the one kfree(msg) below. Anyways
I'll just move these back a bit. Agree it is slightly nicer.

Thanks.