xen-netback: don't produce zero-size SKB frags

commit c7ec4f2d68 upstream.

While frontends may submit zero-size requests (wasting a precious slot),
core networking code as of at least 3ece782693 ("sock: skb_copy_ubufs
support for compound pages") can't deal with SKBs when they have all
zero-size fragments. Respond to empty requests right when populating
fragments; all further processing is fragment based and hence won't
encounter these empty requests anymore.

In a way this should have been that way from the beginning: When no data
is to be transferred for a particular request, there's not even a point
in validating the respective grant ref. That's no different from e.g.
passing NULL into memcpy() when at the same time the size is 0.

This is XSA-448 / CVE-2023-46838.

Cc: stable@vger.kernel.org
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Paul Durrant <paul@xen.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Jan Beulich 2024-01-08 09:55:56 +01:00 • committed by Greg Kroah-Hartman
commit 0179c6b07f