From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:55956) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1gSqtI-0004Nx-1C for qemu-devel@nongnu.org; Fri, 30 Nov 2018 17:04:05 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1gSqtG-0004CB-F6 for qemu-devel@nongnu.org; Fri, 30 Nov 2018 17:04:03 -0500 From: Eric Blake Date: Fri, 30 Nov 2018 16:03:34 -0600 Message-Id: <20181130220344.3350618-6-eblake@redhat.com> In-Reply-To: <20181130220344.3350618-1-eblake@redhat.com> References: <20181130220344.3350618-1-eblake@redhat.com> Subject: [Qemu-devel] [PATCH 05/14] nbd/client: Drop pointless buf variable List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org Cc: jsnow@redhat.com, nsoffer@redhat.com, rjones@redhat.com, vsementsov@virtuozzo.com, qemu-block@nongnu.org There's no need to read into a temporary buffer (oversized since commit 7d3123e1) followed by a byteswap into a uint64_t to check for a magic number via memcmp(), when the code immediately below demonstrates reading into the uint64_t then byteswapping in place and checking for a magic number via integer math. What's more, having a different error message when the server's first reply byte is 0 is unusual - it's no different from any other wrong magic number, and we already detected short reads. Signed-off-by: Eric Blake --- nbd/nbd-internal.h | 1 + nbd/client.c | 14 +++----------- 2 files changed, 4 insertions(+), 11 deletions(-) diff --git a/nbd/nbd-internal.h b/nbd/nbd-internal.h index eeff78d3c98..306a533dcd1 100644 --- a/nbd/nbd-internal.h +++ b/nbd/nbd-internal.h @@ -46,6 +46,7 @@ /* Size of oldstyle negotiation */ #define NBD_OLDSTYLE_NEGOTIATE_SIZE (8 + 8 + 8 + 4 + 124) +#define NBD_INIT_MAGIC 0x4e42444d41474943LL #define NBD_REQUEST_MAGIC 0x25609513 #define NBD_OPTS_MAGIC 0x49484156454F5054LL #define NBD_CLIENT_MAGIC 0x0000420281861253LL diff --git a/nbd/client.c b/nbd/client.c index 0be89f9e641..17ee24492a4 100644 --- a/nbd/client.c +++ b/nbd/client.c @@ -731,7 +731,6 @@ int nbd_receive_negotiate(QIOChannel *ioc, const char *name, QIOChannel **outioc, NBDExportInfo *info, Error **errp) { - char buf[256]; uint64_t magic; int rc; bool zeroes = true; @@ -752,21 +751,14 @@ int nbd_receive_negotiate(QIOChannel *ioc, const char *name, goto fail; } - if (nbd_read(ioc, buf, 8, errp) < 0) { + if (nbd_read(ioc, &magic, sizeof(magic), errp) < 0) { error_prepend(errp, "Failed to read data: "); goto fail; } - - buf[8] = '\0'; - if (strlen(buf) == 0) { - error_setg(errp, "Server connection closed unexpectedly"); - goto fail; - } - - magic = ldq_be_p(buf); + magic = be64_to_cpu(magic); trace_nbd_receive_negotiate_magic(magic); - if (memcmp(buf, "NBDMAGIC", 8) != 0) { + if (magic != NBD_INIT_MAGIC) { error_setg(errp, "Invalid magic received"); goto fail; } -- 2.17.2