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. That whole strlen() issue has been
present and useless since commit 1d45f8b5 in 2010; perhaps it
was leftover debugging (since the correct magic number happens
to be ASCII)? Make the error messages more consistent and
detailed while touching things.
Signed-off-by: Eric Blake
Reviewed-by: Richard W.M. Jones
Reviewed-by: Vladimir Sementsov-Ogievskiy
---
v2: improve commit message based on git archaeology [Rich]
added strategic comments, and improve error messages [Vladimir]
---
nbd/nbd-internal.h | 3 ++-
nbd/client.c | 22 +++---
2 files changed, 9 insertions(+), 16 deletions(-)
diff --git a/nbd/nbd-internal.h b/nbd/nbd-internal.h
index eeff78d3c98..443e177d44a 100644
--- a/nbd/nbd-internal.h
+++ b/nbd/nbd-internal.h
@@ -46,8 +46,9 @@
/* Size of oldstyle negotiation */
#define NBD_OLDSTYLE_NEGOTIATE_SIZE (8 + 8 + 8 + 4 + 124)
+#define NBD_INIT_MAGIC 0x4e42444d41474943LL /* ASCII "NBDMAGIC" */
#define NBD_REQUEST_MAGIC 0x25609513
-#define NBD_OPTS_MAGIC 0x49484156454F5054LL
+#define NBD_OPTS_MAGIC 0x49484156454F5054LL /* ASCII "IHAVEOPT" */
#define NBD_CLIENT_MAGIC0x420281861253LL
#define NBD_REP_MAGIC 0x0003e889045565a9LL
diff --git a/nbd/client.c b/nbd/client.c
index 3d9086af39d..1a3a620fb6d 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;
@@ -752,27 +751,20 @@ int nbd_receive_negotiate(QIOChannel *ioc, const char
*name,
goto fail;
}
-if (nbd_read(ioc, buf, 8, errp) < 0) {
-error_prepend(errp, "Failed to read data: ");
+if (nbd_read(ioc, , sizeof(magic), errp) < 0) {
+error_prepend(errp, "Failed to read initial magic: ");
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) {
-error_setg(errp, "Invalid magic received");
+if (magic != NBD_INIT_MAGIC) {
+error_setg(errp, "Bad initial magic received: 0x%" PRIx64, magic);
goto fail;
}
if (nbd_read(ioc, , sizeof(magic), errp) < 0) {
-error_prepend(errp, "Failed to read magic: ");
+error_prepend(errp, "Failed to read server magic: ");
goto fail;
}
magic = be64_to_cpu(magic);
@@ -911,7 +903,7 @@ int nbd_receive_negotiate(QIOChannel *ioc, const char *name,
}
info->flags = oldflags;
} else {
-error_setg(errp, "Bad magic received");
+error_setg(errp, "Bad server magic received: 0x%" PRIx64, magic);
goto fail;
}
--
2.17.2
