Re: [Libguestfs] [v2v PATCH 1/2] lib/utils: get_disk_allocated: assert that NBD block length is positive

It makes no sense for the NBD server to return a zero-length block, plus it used to be a bug in the libnbd OCaml bindings to wrap 32-bit block lengths with the MSB set around to negative (signed) 32-bit integers (which would then be widened to negative (signed) 64-bit integers). Any non-positive "len" value breaks the progression of "fetch_offset", potentially leading to an infinite loop. Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=2027598 Signed-off-by: Laszlo Ersek <lersek(a)redhat.com&gt; --- lib/utils.ml | 1 + 1 file changed, 1 insertion(+) diff --git a/lib/utils.ml b/lib/utils.ml index 4c43a4b5161d..f599b0e32450 100644 --- a/lib/utils.ml +++ b/lib/utils.ml @@ -197,6 +197,7 @@ let get_disk_allocated ~dir ~disknr = for i = 0 to Array.length entries / 2 - 1 do let len = Int64.of_int32 entries.(i * 2) and typ = entries.(i * 2 + 1) in + assert (len > 0_L); if Int32.logand typ 1_l = 0_l then allocated := !allocated +^ len; fetch_offset := !fetch_offset +^ len -- 2.19.1.3.g30247aa5d201