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Message-ID: <CAEih1qW6_YetJV4LB9=+P-TCd6Bw_YZ=cVaL+tOLxPk=qp1a6A@mail.gmail.com>
Date: Thu, 9 Feb 2023 12:53:54 +0100
From: Pietro Borrello <borrello@...g.uniroma1.it>
To: Xin Long <lucien.xin@...il.com>
Cc: Neil Horman <nhorman@...driver.com>,
Marcelo Ricardo Leitner <marcelo.leitner@...il.com>,
"David S. Miller" <davem@...emloft.net>,
Eric Dumazet <edumazet@...gle.com>,
Jakub Kicinski <kuba@...nel.org>,
Paolo Abeni <pabeni@...hat.com>,
Cristiano Giuffrida <c.giuffrida@...nl>,
"Bos, H.J." <h.j.bos@...nl>, Jakob Koschel <jkl820.git@...il.com>,
linux-sctp@...r.kernel.org, netdev@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next] sctp: check ep asocs list before access
On Wed, 8 Feb 2023 at 20:21, Xin Long <lucien.xin@...il.com> wrote:
>
> [...]
> > We suspect a race condition between a connecting sctp socket
> > and the diag query.
> As it commented in sctp_transport_traverse_process():
>
> "asoc can be peeled off " before callinsctp_sock_filter(). Actually,
Ah, thank you for clarifying! I misunderstood the comment, and read it
like "we hold the ep, otherwise ascoc can be peeled off".
> the asoc can be peeled off from the ep anytime during it by another
> thread, and placing a list_empty(&ep->asocs) check and returning
> won't avoid it completely, as peeling off the asoc can happen after
> your check.
>
> We actually don't care about the asoc peeling off during the dump,
> as sctp diag can not work that accurately. There also shouldn't be
Agree. This makes a lot of sense.
> problems caused so far, as the "assoc" won't be used anywhere after
> that check.
>
> To avoid the "type confused pointer" thing, maybe you can try to use
> list_is_first() there:
>
> - struct sctp_association *assoc =
> - list_entry(ep->asocs.next, struct sctp_association, asocs);
>
> /* find the ep only once through the transports by this condition */
> - if (tsp->asoc != assoc)
> + if (!list_is_first(&tsp->asoc->asocs, &ep->asocs))
> return 0;
>
This is a very nice suggestion, which also avoids future issues in
case assoc would be used. I'll do that in v2. Thank you!
Best regards,
Pietro
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