Re: [Libguestfs] [nbdkit PATCH] nbd: Opt in to libnbd pread_initialize speedup

On Fri, Feb 11, 2022 at 07:14:30AM +0100, Laszlo Ersek wrote: > On 02/10/22 16:38, Eric Blake wrote: >> Our nbd plugin has always properly checked for asynch errors (and thus >> has never been at risk of a vulnerability similar to CVE-2022-0485 >> just fixed in nbdcopy). What's more, the nbdkit core guarantees >> (since commit b1ce255e in 2019, v1.13.1) that the buffer handed to a >> .pread callback has been pre-sanitized to not leak heap contents, >> regardless of how buggy a plugin might be (see >> server/protocol.c:protocol_recv_request_send_reply(), which uses >> server/threadlocal.c:threadlocal_buffer() for a safe buffer). Thus, >> we do not need libnbd to spend time re-initializing the buffer, if >> libnbd is new enough to give us that knob. >> --- >> >> +#if LIBNBD_HAVE_NBD_SET_PREAD_INITIALIZE >> + /* nbdkit guarantees that the buffers passed to our .pread callback >> + * are pre-initialized; and we in turn ensure that the buffer is not >> + * dereferenced if the NBD server replied with an error. Thus, we >> + * are safe opting in to this libnbd speedup. >> + */ >> + if (nbd_set_pread_initialize (h->nbd, false) == -1) >> + goto errnbd; >> #endif >> if (dynamic_export && uri) { >> #if LIBNBD_HAVE_NBD_SET_OPT_MODE >> > > hahaha, this was real quick ;) I don't know if the speedy pun was intentional ;)

Now pushed as 31997b25.