Re: [Libguestfs] [PATCH nbdkit 1/2] ocaml: Initialize pread buffer with zeroes to avoid leaking heap memory.

In the C part of the OCaml plugin we create a ‘bytes’ [byte array] and pass it to the OCaml pread method. The plugin should overwrite the array with the returned data. However if (eg. because of a bug) the plugin does not fill the array then whatever was in the OCaml or possibly even the C heap before the allocation is returned to the client, possibly resulting in a leak of sensitive data. We can avoid this by initializing the array with zeroes. Credit: Eric Blake for finding the bug. --- plugins/ocaml/ocaml.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/plugins/ocaml/ocaml.c b/plugins/ocaml/ocaml.c index d854f48..7193842 100644 --- a/plugins/ocaml/ocaml.c +++ b/plugins/ocaml/ocaml.c @@ -444,6 +444,10 @@ pread_wrapper (void *h, void *buf, uint32_t count, uint64_t offset, caml_leave_blocking_section (); strv = caml_alloc_string (count); + /* Initialize the buffer with zeroes in case the plugin does not + * fill it completely. + */ + memset (String_val (strv), 0, count); offsetv = caml_copy_int64 (offset); flagsv = Val_flags (flags);