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[Qemu-devel] [PULL 7/7] nbd-client: Fix regression when server sends gar
From: |
Eric Blake |
Subject: |
[Qemu-devel] [PULL 7/7] nbd-client: Fix regression when server sends garbage |
Date: |
Tue, 15 Aug 2017 10:09:07 -0500 |
When we switched NBD to use coroutines for qemu 2.9 (in particular,
commit a12a712a), we introduced a regression: if a server sends us
garbage (such as a corrupted magic number), we quit the read loop
but do not stop sending further queued commands, resulting in the
client hanging when it never reads the response to those additional
commands. In qemu 2.8, we properly detected that the server is no
longer reliable, and cancelled all existing pending commands with
EIO, then tore down the socket so that all further command attempts
get EPIPE.
Restore the proper behavior of quitting (almost) all communication
with a broken server: Once we know we are out of sync or otherwise
can't trust the server, we must assume that any further incoming
data is unreliable and therefore end all pending commands with EIO,
and quit trying to send any further commands. As an exception, we
still (try to) send NBD_CMD_DISC to let the server know we are going
away (in part, because it is easier to do that than to further
refactor nbd_teardown_connection, and in part because it is the
only command where we do not have to wait for a reply).
Based on a patch by Vladimir Sementsov-Ogievskiy.
A malicious server can be created with the following hack,
followed by setting NBD_SERVER_DEBUG to a non-zero value in the
environment when running qemu-nbd:
| --- a/nbd/server.c
| +++ b/nbd/server.c
| @@ -919,6 +919,17 @@ static int nbd_send_reply(QIOChannel *ioc, NBDReply
*reply, Error **errp)
| stl_be_p(buf + 4, reply->error);
| stq_be_p(buf + 8, reply->handle);
|
| + static int debug;
| + static int count;
| + if (!count++) {
| + const char *str = getenv("NBD_SERVER_DEBUG");
| + if (str) {
| + debug = atoi(str);
| + }
| + }
| + if (debug && !(count % debug)) {
| + buf[0] = 0;
| + }
| return nbd_write(ioc, buf, sizeof(buf), errp);
| }
Reported-by: Vladimir Sementsov-Ogievskiy <address@hidden>
Signed-off-by: Eric Blake <address@hidden>
Message-Id: <address@hidden>
Reviewed-by: Stefan Hajnoczi <address@hidden>
---
block/nbd-client.h | 1 +
block/nbd-client.c | 17 +++++++++++++----
2 files changed, 14 insertions(+), 4 deletions(-)
diff --git a/block/nbd-client.h b/block/nbd-client.h
index df80771357..1935ffbcaa 100644
--- a/block/nbd-client.h
+++ b/block/nbd-client.h
@@ -29,6 +29,7 @@ typedef struct NBDClientSession {
Coroutine *recv_coroutine[MAX_NBD_REQUESTS];
NBDReply reply;
+ bool quit;
} NBDClientSession;
NBDClientSession *nbd_get_client_session(BlockDriverState *bs);
diff --git a/block/nbd-client.c b/block/nbd-client.c
index 25dd28406b..422ecb4307 100644
--- a/block/nbd-client.c
+++ b/block/nbd-client.c
@@ -73,7 +73,7 @@ static coroutine_fn void nbd_read_reply_entry(void *opaque)
int ret;
Error *local_err = NULL;
- for (;;) {
+ while (!s->quit) {
assert(s->reply.handle == 0);
ret = nbd_receive_reply(s->ioc, &s->reply, &local_err);
if (ret < 0) {
@@ -107,6 +107,9 @@ static coroutine_fn void nbd_read_reply_entry(void *opaque)
qemu_coroutine_yield();
}
+ if (ret < 0) {
+ s->quit = true;
+ }
nbd_recv_coroutines_enter_all(s);
s->read_reply_co = NULL;
}
@@ -135,6 +138,10 @@ static int nbd_co_send_request(BlockDriverState *bs,
assert(i < MAX_NBD_REQUESTS);
request->handle = INDEX_TO_HANDLE(s, i);
+ if (s->quit) {
+ qemu_co_mutex_unlock(&s->send_mutex);
+ return -EIO;
+ }
if (!s->ioc) {
qemu_co_mutex_unlock(&s->send_mutex);
return -EPIPE;
@@ -143,7 +150,7 @@ static int nbd_co_send_request(BlockDriverState *bs,
if (qiov) {
qio_channel_set_cork(s->ioc, true);
rc = nbd_send_request(s->ioc, request);
- if (rc >= 0) {
+ if (rc >= 0 && !s->quit) {
ret = nbd_rwv(s->ioc, qiov->iov, qiov->niov, request->len, false,
NULL);
if (ret != request->len) {
@@ -154,6 +161,9 @@ static int nbd_co_send_request(BlockDriverState *bs,
} else {
rc = nbd_send_request(s->ioc, request);
}
+ if (rc < 0) {
+ s->quit = true;
+ }
qemu_co_mutex_unlock(&s->send_mutex);
return rc;
}
@@ -168,8 +178,7 @@ static void nbd_co_receive_reply(NBDClientSession *s,
/* Wait until we're woken up by nbd_read_reply_entry. */
qemu_coroutine_yield();
*reply = s->reply;
- if (reply->handle != request->handle ||
- !s->ioc) {
+ if (reply->handle != request->handle || !s->ioc || s->quit) {
reply->error = EIO;
} else {
if (qiov && reply->error == 0) {
--
2.13.5
- [Qemu-devel] [PULL for 2.10-rc3 0/7] NBD changes for 2.10-rc3, Eric Blake, 2017/08/15
- [Qemu-devel] [PULL 1/7] nbd: Fix trace message for disconnect, Eric Blake, 2017/08/15
- [Qemu-devel] [PULL 2/7] qemu-iotests: step clock after each test iteration, Eric Blake, 2017/08/15
- [Qemu-devel] [PULL 3/7] stubs: Add vm state change handler stubs, Eric Blake, 2017/08/15
- [Qemu-devel] [PULL 5/7] block-backend: Defer shared_perm tightening migration completion, Eric Blake, 2017/08/15
- [Qemu-devel] [PULL 4/7] nbd: Fix order of bdrv_set_perm and bdrv_invalidate_cache, Eric Blake, 2017/08/15
- [Qemu-devel] [PULL 7/7] nbd-client: Fix regression when server sends garbage,
Eric Blake <=
- Re: [Qemu-devel] [PULL 7/7] nbd-client: Fix regression when server sends garbage, Vladimir Sementsov-Ogievskiy, 2017/08/21
[Qemu-devel] [PULL 6/7] iotests: Add non-shared storage migration case 192, Eric Blake, 2017/08/15
Re: [Qemu-devel] [PULL for 2.10-rc3 0/7] NBD changes for 2.10-rc3, Peter Maydell, 2017/08/15