[Libguestfs] [nbdkit PATCH v2 3/5] nbd: Implement structured reads from server
Eric Blake
eblake at redhat.com
Thu Apr 25 18:01:44 UTC 2019
Time to enhance the nbd plugin to request structured replies from the
server. For now, deal only with structured reads. The server can now
return sparse reads, even though we need to design nbdkit version 3
before we can in turn return sparse reads back to the client.
In general, we have to assume the server is malicious, and so we must
sanity check that it sends replies we expect, and kill the connection
if we detect protocol non-compliance that may affect our ability to
further communicate with the server. However, we have a choice between
either implementing bookkeeping to ensure that the server sends
exactly as many non-overlapping chunks as needed to cover the entire
read request, or else assuming that the server was compliant. Since
nbdkit was just recently patched to ensure that a plugin that does not
make a full reply will merely be exposing data used in a previous read
or write command, we don't bother to pre-wipe the buffer or add any
reconstruction bookkeeping (if our assumption about a compliant server
is wrong, the client may notice confusing results because of the stale
data being replayed at server-omitted offsets, but the data corruption
fault then lies in the non-compliant server).
Signed-off-by: Eric Blake <eblake at redhat.com>
---
plugins/nbd/nbd.c | 140 ++++++++++++++++++++++++++++++++++++++++++++--
1 file changed, 136 insertions(+), 4 deletions(-)
diff --git a/plugins/nbd/nbd.c b/plugins/nbd/nbd.c
index 1d3b2a3..b2b3075 100644
--- a/plugins/nbd/nbd.c
+++ b/plugins/nbd/nbd.c
@@ -340,9 +340,14 @@ nbd_reply_raw (struct handle *h, int *fd)
} rep;
struct transaction *trans;
void *buf = NULL;
+ CLEANUP_FREE char *payload = NULL;
uint32_t count;
int error = NBD_SUCCESS;
bool more = false;
+ uint32_t len = 0; /* 0 except for structured reads */
+ uint64_t offset = 0; /* if len, absolute offset of structured read chunk */
+ bool zero = false; /* if len, whether to read or memset */
+ uint16_t errlen;
*fd = -1;
/* magic and handle overlap between simple and structured replies */
@@ -361,9 +366,100 @@ nbd_reply_raw (struct handle *h, int *fd)
nbdkit_error ("structured response without negotiation");
return nbd_mark_dead (h);
}
- /* TODO - set 'more' based on NBD_REPLY_FLAG_DONE, parse the
- various reply types, etc. */
- abort ();
+ if (read_full (h->fd, sizeof rep.simple + (char *) &rep,
+ sizeof rep - sizeof rep.simple))
+ return nbd_mark_dead (h);
+ rep.structured.flags = be16toh (rep.structured.flags);
+ rep.structured.type = be16toh (rep.structured.type);
+ rep.structured.length = be32toh (rep.structured.length);
+ nbdkit_debug ("received structured reply %s for cookie %#" PRIx64
+ ", payload length %" PRId32,
+ name_of_nbd_reply_type(rep.structured.type),
+ rep.structured.handle, rep.structured.length);
+ if (rep.structured.length > 64 * 1024 * 1024) {
+ nbdkit_error ("structured reply length is suspiciously large: %" PRId32,
+ rep.structured.length);
+ return nbd_mark_dead (h);
+ }
+ if (rep.structured.length) {
+ /* Special case for OFFSET_DATA in order to read tail of chunk
+ directly into final buffer later on */
+ len = (rep.structured.type == NBD_REPLY_TYPE_OFFSET_DATA &&
+ rep.structured.length > sizeof offset) ? sizeof offset :
+ rep.structured.length;
+ payload = malloc (len);
+ if (!payload) {
+ nbdkit_error ("reading structured reply payload: %m");
+ return nbd_mark_dead (h);
+ }
+ if (read_full (h->fd, payload, len))
+ return nbd_mark_dead (h);
+ len = 0;
+ }
+ more = !(rep.structured.flags & NBD_REPLY_FLAG_DONE);
+ switch (rep.structured.type) {
+ case NBD_REPLY_TYPE_NONE:
+ if (rep.structured.length) {
+ nbdkit_error ("NBD_REPLY_TYPE_NONE with invalid payload");
+ return nbd_mark_dead (h);
+ }
+ if (more) {
+ nbdkit_error ("NBD_REPLY_TYPE_NONE without done flag");
+ return nbd_mark_dead (h);
+ }
+ break;
+ case NBD_REPLY_TYPE_OFFSET_DATA:
+ if (rep.structured.length <= sizeof offset) {
+ nbdkit_error ("structured reply OFFSET_DATA too small");
+ return nbd_mark_dead (h);
+ }
+ memcpy (&offset, payload, sizeof offset);
+ offset = be64toh (offset);
+ len = rep.structured.length - sizeof offset;
+ break;
+ case NBD_REPLY_TYPE_OFFSET_HOLE:
+ if (rep.structured.length != sizeof offset + sizeof len) {
+ nbdkit_error ("structured reply OFFSET_HOLE size incorrect");
+ return nbd_mark_dead (h);
+ }
+ memcpy (&offset, payload, sizeof offset);
+ offset = be64toh (offset);
+ memcpy (&len, payload, sizeof len);
+ len = be32toh (len);
+ if (!len) {
+ nbdkit_error ("structured reply OFFSET_HOLE length incorrect");
+ return nbd_mark_dead (h);
+ }
+ zero = true;
+ break;
+ default:
+ if (!NBD_REPLY_TYPE_IS_ERR (rep.structured.type)) {
+ nbdkit_error ("received unexpected structured reply %s",
+ name_of_nbd_reply_type(rep.structured.type));
+ return nbd_mark_dead (h);
+ }
+
+ if (rep.structured.length < sizeof error + sizeof errlen) {
+ nbdkit_error ("structured reply error size incorrect");
+ return nbd_mark_dead (h);
+ }
+ memcpy (&errlen, payload + sizeof error, sizeof errlen);
+ errlen = be16toh (errlen);
+ if (errlen > rep.structured.length - sizeof error - sizeof errlen) {
+ nbdkit_error ("structured reply error message size incorrect");
+ return nbd_mark_dead (h);
+ }
+ memcpy (&error, payload, sizeof error);
+ error = be32toh (error);
+ if (errlen)
+ nbdkit_debug ("received structured error %s with message: %.*s",
+ name_of_nbd_error (error), (int) errlen,
+ payload + sizeof error + sizeof errlen);
+ else
+ nbdkit_debug ("received structured error %s without message",
+ name_of_nbd_error (error));
+ }
+ break;
default:
nbdkit_error ("received unexpected magic in reply: %#" PRIx32,
@@ -383,6 +479,24 @@ nbd_reply_raw (struct handle *h, int *fd)
nbdkit_error ("simple read reply when structured was expected");
return nbd_mark_dead (h);
}
+ if (len) {
+ if (!buf) {
+ nbdkit_error ("structured read response to a non-read command");
+ return nbd_mark_dead (h);
+ }
+ if (offset < trans->offset || offset > INT64_MAX ||
+ offset + len > trans->offset + count) {
+ nbdkit_error ("structured read reply with unexpected offset/length");
+ return nbd_mark_dead (h);
+ }
+ buf = (char *) buf + offset - trans->offset;
+ if (zero) {
+ memset (buf, 0, len);
+ buf = NULL;
+ }
+ else
+ count = len;
+ }
/* Thanks to structured replies, we must preserve an error in any
earlier chunk for replay during the final chunk. */
@@ -556,7 +670,25 @@ nbd_newstyle_haggle (struct handle *h)
uint16_t nrinfos = htobe16 (0);
struct fixed_new_option_reply reply;
- /* TODO: structured reads, block status */
+ nbdkit_debug ("trying NBD_OPT_STRUCTURED_REPLY");
+ opt.version = htobe64 (NEW_VERSION);
+ opt.option = htobe32 (NBD_OPT_STRUCTURED_REPLY);
+ opt.optlen = htobe32 (0);
+ if (write_full (h->fd, &opt, sizeof opt)) {
+ nbdkit_error ("unable to request NBD_OPT_STRUCTURED_REPLY: %m");
+ return -1;
+ }
+ if (nbd_newstyle_recv_option_reply (h, NBD_OPT_STRUCTURED_REPLY, &reply,
+ NULL) < 0)
+ return -1;
+ if (reply.reply == NBD_REP_ACK) {
+ nbdkit_debug ("structured replies enabled");
+ h->structured = true;
+ /* TODO: block status */
+ }
+ else {
+ nbdkit_debug ("structured replies disabled");
+ }
/* Try NBD_OPT_GO */
nbdkit_debug ("trying NBD_OPT_GO");
--
2.20.1
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