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

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Message-ID: <046f2c47-53c7-461e-a5b0-8fe4ae0faacc@rbox.co>
Date: Mon, 9 Dec 2024 10:54:03 +0100
From: Michal Luczaj <mhal@...x.co>
To: John Fastabend <john.fastabend@...il.com>,
 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>, 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
Subject: Re: [PATCH bpf 1/3] bpf, sockmap: Fix update element with same

On 12/9/24 06:47, John Fastabend wrote:
> 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>

Thanks, and sorry for a missing tag:

Fixes: 604326b41a6f ("bpf, sockmap: convert to generic sk_msg interface")