Re: [PATCH v2 1/2] vhost: fix possible FDs leak

[David Marchand <david.marchand@redhat.com>]

On Mon, Jan 30, 2023 at 10:46 AM Maxime Coquelin
<maxime.coquelin@redhat.com> wrote:
>
>
>
> On 1/29/23 10:25, David Marchand wrote:
> > On Fri, Jan 27, 2023 at 5:55 PM Maxime Coquelin
> > <maxime.coquelin@redhat.com> wrote:
> >>
> >> On failure, read_vhost_message() only closed the message
> >> FDs if the header size was unexpected, but there are other
> >> cases where it is required. For exemple in the case the
> >> payload size read from the header is greater than the
> >> expected maximum payload size.
> >>
> >> This patch fixes this by closing all messages FDs in all
> >> error cases.
> >>
> >> Fixes: bf472259dde6 ("vhost: fix possible denial of service by leaking FDs")
> >> Cc: stable@dpdk.org
> >>
> >> Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com>
> >
> > Reviewed-by: David Marchand <david.marchand@redhat.com>
> >
> > We mentionned offlist that the request type can be logged to help with debug.
> > Do you intend to add this as a follow up patch?
> >
> >
>
> Thinking about it, that's not that trivial because read_vhost_message()
> is called for both master and slave channels, so we would need to
> differentiate between both to print proper request name.
>
> It is doable by comparing the file descriptor passed as parameter with
> the slave one stored in struct virtio_net, but that's not super clean.

From the 3 different callers of read_vhost_message, I think the only
one that could gain from this debug is vhost_user_msg_handler().

And here, we could look at the message content on read_vhost_message return.
Like this untested and ugly snippet:

diff --git a/lib/vhost/vhost_user.c b/lib/vhost/vhost_user.c
index 943058725e..1556f21a58 100644
--- a/lib/vhost/vhost_user.c
+++ b/lib/vhost/vhost_user.c
@@ -2994,13 +2994,10 @@ vhost_user_msg_handler(int vid, int fd)
                }
        }

+       ctx.msg.request.master = VHOST_USER_NONE;
        ret = read_vhost_message(dev, fd, &ctx);
-       if (ret <= 0) {
-               if (ret < 0)
-                       VHOST_LOG_CONFIG(dev->ifname, ERR, "vhost read
message failed\n");
-               else
-                       VHOST_LOG_CONFIG(dev->ifname, INFO, "vhost
peer closed\n");
-
+       if (ret == 0) {
+               VHOST_LOG_CONFIG(dev->ifname, INFO, "vhost peer closed\n");
                return -1;
        }

@@ -3010,6 +3007,14 @@ vhost_user_msg_handler(int vid, int fd)
        else
                msg_handler = NULL;

+       if (ret < 0) {
+               VHOST_LOG_CONFIG(dev->ifname, ERR, "vhost read message
%s%s%sfailed\n",
+                       msg_handler != NULL ? "for " : "",
+                       msg_handler != NULL ? msg_handler->description : "",
+                       msg_handler != NULL ? " " : "");
+               return -1;
+       }
+
        if (msg_handler != NULL && msg_handler->description != NULL) {
                if (request != VHOST_USER_IOTLB_MSG)
                        VHOST_LOG_CONFIG(dev->ifname, INFO,


-- 
David Marchand