Patchwork [4/4] chardev: clear O_NONBLOCK on SCM_RIGHTS file descriptors

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Submitter Stefan Hajnoczi
Date March 26, 2013, 4:07 p.m.
Message ID <1364314072-2474-5-git-send-email-stefanha@redhat.com>
Download mbox | patch
Permalink /patch/231425/
State New
Headers show

Comments

Stefan Hajnoczi - March 26, 2013, 4:07 p.m.
When we receive a file descriptor over a UNIX domain socket the
O_NONBLOCK flag is preserved.  Clear the O_NONBLOCK flag and rely on
QEMU file descriptor users like migration, SPICE, VNC, block layer, and
others to set non-blocking only when necessary.

This change ensures we don't accidentally expose O_NONBLOCK in the QMP
API.  QMP clients should not need to get the non-blocking state
"correct".

A recent real-world example was when libvirt passed a non-blocking TCP
socket for migration where we expected a blocking socket.  The source
QEMU produced a corrupted migration stream since its code did not cope
with non-blocking sockets.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
---
 qemu-char.c | 3 +++
 1 file changed, 3 insertions(+)
Juan Quintela - March 26, 2013, 4:38 p.m.
Stefan Hajnoczi <stefanha@redhat.com> wrote:
> When we receive a file descriptor over a UNIX domain socket the
> O_NONBLOCK flag is preserved.  Clear the O_NONBLOCK flag and rely on
> QEMU file descriptor users like migration, SPICE, VNC, block layer, and
> others to set non-blocking only when necessary.
>
> This change ensures we don't accidentally expose O_NONBLOCK in the QMP
> API.  QMP clients should not need to get the non-blocking state
> "correct".
>
> A recent real-world example was when libvirt passed a non-blocking TCP
> socket for migration where we expected a blocking socket.  The source
> QEMU produced a corrupted migration stream since its code did not cope
> with non-blocking sockets.
>
> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

Acked-by: Juan Quintela <quintela@redhat.com>
Eric Blake - March 26, 2013, 4:40 p.m.
On 03/26/2013 10:07 AM, Stefan Hajnoczi wrote:
> When we receive a file descriptor over a UNIX domain socket the
> O_NONBLOCK flag is preserved.  Clear the O_NONBLOCK flag and rely on
> QEMU file descriptor users like migration, SPICE, VNC, block layer, and
> others to set non-blocking only when necessary.
> 
> This change ensures we don't accidentally expose O_NONBLOCK in the QMP
> API.  QMP clients should not need to get the non-blocking state
> "correct".
> 
> A recent real-world example was when libvirt passed a non-blocking TCP
> socket for migration where we expected a blocking socket.  The source
> QEMU produced a corrupted migration stream since its code did not cope
> with non-blocking sockets.
> 
> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> ---
>  qemu-char.c | 3 +++
>  1 file changed, 3 insertions(+)

Reviewed-by: Eric Blake <eblake@redhat.com>

Covers both 'getfd' and 'add-fd' paths.

Patch

diff --git a/qemu-char.c b/qemu-char.c
index 8fb8340..e50b1b3 100644
--- a/qemu-char.c
+++ b/qemu-char.c
@@ -2407,6 +2407,9 @@  static void unix_process_msgfd(CharDriverState *chr, struct msghdr *msg)
         if (fd < 0)
             continue;
 
+        /* O_NONBLOCK is preserved across SCM_RIGHTS so reset it */
+        qemu_set_block(fd);
+
 #ifndef MSG_CMSG_CLOEXEC
         qemu_set_cloexec(fd);
 #endif