netdev - Re: [PATCH] net: sockmap: Don't call bpf_prog

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Date:   Wed, 14 Oct 2020 21:43:30 -0700
From:   John Fastabend <john.fastabend@...il.com>
To:     Jakub Sitnicki <jakub@...udflare.com>,
        Alex Dewar <alex.dewar90@...il.com>
Cc:     John Fastabend <john.fastabend@...il.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Lorenz Bauer <lmb@...udflare.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        Andrii Nakryiko <andrii@...nel.org>,
        KP Singh <kpsingh@...omium.org>, netdev@...r.kernel.org,
        bpf@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] net: sockmap: Don't call bpf_prog_put() on NULL pointer

Jakub Sitnicki wrote:
> On Mon, Oct 12, 2020 at 07:09 PM CEST, Alex Dewar wrote:
> > If bpf_prog_inc_not_zero() fails for skb_parser, then bpf_prog_put() is
> > called unconditionally on skb_verdict, even though it may be NULL. Fix
> > and tidy up error path.
> >
> > Addresses-Coverity-ID: 1497799: Null pointer dereferences (FORWARD_NULL)
> > Fixes: 743df8b7749f ("bpf, sockmap: Check skb_verdict and skb_parser programs explicitly")
> > Signed-off-by: Alex Dewar <alex.dewar90@...il.com>
> > ---
> 
> Acked-by: Jakub Sitnicki <jakub@...udflare.com>

Thanks.

Jakub, any opinions on if we should just throw an error if users try to
add a sock to a map with a parser but no verdict? At the moment we fall
through and add the socket, but it wont do any receive parsing/verdict.
At the moment I think its fine with above fix. The useful cases for RX
are parser+verdict, verdict, and empty. Where empty is just used for
redirects or other socket account tricks. Just something to keep in mind.

Acked-by: John Fastabend <john.fastabend@...il.com>