netdev - Re: [PATCH net 2/2] selftests: net: add a test for closing a netlink socket ith dump in progress

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Message-ID: <20241105062107.64837-1-kuniyu@amazon.com>
Date: Mon, 4 Nov 2024 22:21:07 -0800
From: Kuniyuki Iwashima <kuniyu@...zon.com>
To: <kuba@...nel.org>
CC: <davem@...emloft.net>, <edumazet@...gle.com>, <johannes@...solutions.net>,
	<netdev@...r.kernel.org>, <pabeni@...hat.com>, <pablo@...filter.org>,
	<kuniyu@...zon.com>
Subject: Re: [PATCH net 2/2] selftests: net: add a test for closing a netlink socket ith dump in progress

From: Jakub Kicinski <kuba@...nel.org>
Date: Mon,  4 Nov 2024 17:03:47 -0800
> Close a socket with dump in progress. We need a dump which generates
> enough info not to fit into a single skb. Policy dump fits the bill.
> 
> Use the trick discovered by syzbot for keeping a ref on the socket
> longer than just close, with mqueue.
> 
>   TAP version 13
>   1..3
>   # Starting 3 tests from 1 test cases.
>   #  RUN           global.test_sanity ...
>   #            OK  global.test_sanity
>   ok 1 global.test_sanity
>   #  RUN           global.close_in_progress ...
>   #            OK  global.close_in_progress
>   ok 2 global.close_in_progress
>   #  RUN           global.close_with_ref ...
>   #            OK  global.close_with_ref
>   ok 3 global.close_with_ref
>   # PASSED: 3 / 3 tests passed.
>   # Totals: pass:3 fail:0 xfail:0 xpass:0 skip:0 error:0
> 
> Note that this test is not expected to fail but rather crash
> the kernel if we get the cleanup wrong.
> 
> Signed-off-by: Jakub Kicinski <kuba@...nel.org>

Reviewed-by: Kuniyuki Iwashima <kuniyu@...zon.com>

TIL mq_notify, and the trick was interesting that calls fdget(),
netlink_getsockbyfilp(), and fdput() to keep sock_hold() only :)