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-next>] [day] [month] [year] [list]
Date:   Mon, 18 Jul 2022 08:12:52 +0000
From:   Arseniy Krasnov <>
To:     Stefano Garzarella <>,
        "David S. Miller" <>,
        Jakub Kicinski <>,
        Paolo Abeni <>,
        Stefan Hajnoczi <>,
        "Michael S. Tsirkin" <>,
        Arseniy Krasnov <>,
        Krasnov Arseniy <>
CC:     "" <>,
        "" <>,
        "" <>,
        kernel <>
Subject: [RFC PATCH v1 0/3] virtio/vsock: use SO_RCVLOWAT to set


during my experiments with zerocopy receive, i found, that in some
cases, poll() implementation violates POSIX: when socket has non-
default SO_RCVLOWAT(e.g. not 1), poll() will always set POLLIN and
POLLRDNORM bits in 'revents' even number of bytes available to read
on socket is smaller than SO_RCVLOWAT value. In this case,user sees
POLLIN flag and then tries to read data(for example using  'read()'
call), but read call will be blocked, because  SO_RCVLOWAT logic is
supported in dequeue loop in af_vsock.c. But the same time,  POSIX
requires that:

"POLLIN     Data other than high-priority data may be read without
 POLLRDNORM Normal data may be read without blocking."

See, page 293.

So, we have, that poll() syscall returns POLLIN, but read call will
be blocked.

Also in man page socket(7) i found that:

"Since Linux 2.6.28, select(2), poll(2), and epoll(7) indicate a
socket as readable only if at least SO_RCVLOWAT bytes are available."

I checked TCP callback for poll()(net/ipv4/tcp.c, tcp_poll()), it
uses SO_RCVLOWAT value to set POLLIN bit, also i've tested TCP with
this case for TCP socket, it works as POSIX required.

I've added some fixes to af_vsock.c and virtio_transport_common.c,
test is also implemented.

What do You think guys?

Thank You

Arseniy Krasnov(3):
 vsock_test: POLLIN + SO_RCVLOWAT test.
 virtio/vsock: use 'target' in notify_poll_in callback.
 vsock: use sk_skrcvlowat to set POLLIN,POLLRDNORM bits.

 net/vmw_vsock/af_vsock.c                |  2 +-
 net/vmw_vsock/virtio_transport_common.c |  2 +-
 tools/testing/vsock/vsock_test.c        | 90 +++++++++++++++++++++++++++++++++
 3 files changed, 92 insertions(+), 2 deletions(-)


Powered by blists - more mailing lists