ui/vnc-clipboard: fix infinite loop in inflate_buffer (CVE-2023-3255)

ui/vnc-clipboard: fix infinite loop in inflate_buffer (CVE-2023-3255)

A wrong exit condition may lead to an infinite loop when inflating a
valid zlib buffer containing some extra bytes in the `inflate_buffer`
function. The bug only occurs post-authentication. Return the buffer
immediately if the end of the compressed data has been reached
(Z_STREAM_END).

Fixes: CVE-2023-3255
Fixes: 0bf41cab ("ui/vnc: clipboard support")
Reported-by: Kevin Denis <kevin.denis@synacktiv.com>
Signed-off-by: Mauro Matteo Cascella <mcascell@redhat.com>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Tested-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-ID: <20230704084210.101822-1-mcascell@redhat.com>
(cherry picked from commit d921fea338c1059a27ce7b75309d7a2e485f710b)
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>