netdev - RE: [PATCH bpf 1/3] bpf, sockmap: Fix update element with same

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Message-ID: <675684786d66c_1abf208ea@john.notmuch>
Date: Sun, 08 Dec 2024 21:47:36 -0800
From: John Fastabend <john.fastabend@...il.com>
To: Michal Luczaj <mhal@...x.co>, 
 Andrii Nakryiko <andrii@...nel.org>, 
 Eduard Zingerman <eddyz87@...il.com>, 
 Mykola Lysenko <mykolal@...com>, 
 Alexei Starovoitov <ast@...nel.org>, 
 Daniel Borkmann <daniel@...earbox.net>, 
 Martin KaFai Lau <martin.lau@...ux.dev>, 
 Song Liu <song@...nel.org>, 
 Yonghong Song <yonghong.song@...ux.dev>, 
 John Fastabend <john.fastabend@...il.com>, 
 KP Singh <kpsingh@...nel.org>, 
 Stanislav Fomichev <sdf@...ichev.me>, 
 Hao Luo <haoluo@...gle.com>, 
 Jiri Olsa <jolsa@...nel.org>, 
 Shuah Khan <shuah@...nel.org>, 
 Jakub Sitnicki <jakub@...udflare.com>, 
 "David S. Miller" <davem@...emloft.net>, 
 Eric Dumazet <edumazet@...gle.com>, 
 Jakub Kicinski <kuba@...nel.org>, 
 Paolo Abeni <pabeni@...hat.com>, 
 Simon Horman <horms@...nel.org>
Cc: bpf@...r.kernel.org, 
 linux-kselftest@...r.kernel.org, 
 netdev@...r.kernel.org, 
 Michal Luczaj <mhal@...x.co>
Subject: RE: [PATCH bpf 1/3] bpf, sockmap: Fix update element with same

Michal Luczaj wrote:
> Consider a sockmap entry being updated with the same socket:
> 
> 	osk = stab->sks[idx];
> 	sock_map_add_link(psock, link, map, &stab->sks[idx]);
> 	stab->sks[idx] = sk;
> 	if (osk)
> 		sock_map_unref(osk, &stab->sks[idx]);
> 
> Due to sock_map_unref(), which invokes sock_map_del_link(), all the psock's
> links for stab->sks[idx] are torn:
> 
> 	list_for_each_entry_safe(link, tmp, &psock->link, list) {
> 		if (link->link_raw == link_raw) {
> 			...
> 			list_del(&link->list);
> 			sk_psock_free_link(link);
> 		}
> 	}
> 
> And that includes the new link sock_map_add_link() added just before the
> unref.
> 
> This results in a sockmap holding a socket, but without the respective
> link. This in turn means that close(sock) won't trigger the cleanup, i.e. a
> closed socket will not be automatically removed from the sockmap.
> 
> Stop tearing the links when a matching link_raw is found.
> 
> Signed-off-by: Michal Luczaj <mhal@...x.co>
> ---

Thanks. LGTM.

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

>  net/core/sock_map.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/net/core/sock_map.c b/net/core/sock_map.c
> index 78347d7d25ef31525f8ec0a755a18e5793ad92c0..20b348b1964a10a1b0bfbe1a90a4a4cd99715b81 100644
> --- a/net/core/sock_map.c
> +++ b/net/core/sock_map.c
> @@ -159,6 +159,7 @@ static void sock_map_del_link(struct sock *sk,
>  				verdict_stop = true;
>  			list_del(&link->list);
>  			sk_psock_free_link(link);
> +			break;
>  		}
>  	}
>  	spin_unlock_bh(&psock->link_lock);
> 
> -- 
> 2.46.2
>