netdev - Re: [PATCH net] udp: call sock_def_readable() if socket is not SOCK

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CANn89iLF_0__Ewy9TXpCs7NP4FB-18iGfnn=cXgXu4qMbxyhwQ@mail.gmail.com>
Date: Tue, 26 Nov 2024 20:26:56 +0100
From: Eric Dumazet <edumazet@...gle.com>
To: "Fernando F. Mancera" <ffmancera@...eup.net>
Cc: netdev@...r.kernel.org, willemb@...gle.com
Subject: Re: [PATCH net] udp: call sock_def_readable() if socket is not SOCK_FASYNC

On Tue, Nov 26, 2024 at 8:18 PM Fernando F. Mancera
<ffmancera@...eup.net> wrote:
>
> Hi,
>
> On 26/11/2024 19:41, Eric Dumazet wrote:
> > On Tue, Nov 26, 2024 at 7:32 PM Eric Dumazet <edumazet@...gle.com> wrote:
> >>
> >> On Tue, Nov 26, 2024 at 6:56 PM Fernando Fernandez Mancera
> >> <ffmancera@...eup.net> wrote:
> >>>
> >>> If a socket is not SOCK_FASYNC, sock_def_readable() needs to be called
> >>> even if receive queue was not empty. Otherwise, if several threads are
> >>> listening on the same socket with blocking recvfrom() calls they might
> >>> hang waiting for data to be received.
> >>>
> >>
> >> SOCK_FASYNC seems completely orthogonal to the issue.
> >>
> >> First sock_def_readable() should wakeup all threads, I wonder what is happening.
> >
>
> Well, it might be. But I noticed that if SOCK_FASYNC is set then
> sk_wake_async_rcu() do its work and everything is fine. This is why I
> thought checking on the flag was a good idea.
>

How have you tested SOCK_FASYNC ?

SOCK_FASYNC is sending signals. If SIGIO is blocked, I am pretty sure
the bug is back.


> > Oh well, __skb_wait_for_more_packets() is using
> > prepare_to_wait_exclusive(), so in this case sock_def_readable() is
> > waking only one thread.
> >
>
> Yes, this is what I was expecting. What would be the solution? Should I
> change it to "prepare_to_wait()" instead? Although, I don't know the
> implication that change might have.

Sadly, we will have to revert, this exclusive wake is subtle.