libceph: fix preallocation check in get_reply()

commit f2be82b0 upstream.

The check that makes sure that we have enough memory allocated to read
in the entire header of the message in question is currently busted.
It compares front_len of the incoming message with iov_len field of
ceph_msg::front structure, which is used primarily to indicate the
amount of data already read in, and not the size of the allocated
buffer.  Under certain conditions (e.g. a short read from a socket
followed by that socket's shutdown and owning ceph_connection reset)
this results in a warning similar to

[85688.975866] libceph: get_reply front 198 > preallocated 122 (4#0)

and, through another bug, leads to forever hung tasks and forced
reboots.  Fix this by comparing front_len with front_alloc_len field of
struct ceph_msg, which stores the actual size of the buffer.

Fixes: http://tracker.ceph.com/issues/5425Signed-off-by: Ilya Dryomov <ilya.dryomov@inktank.com>
Reviewed-by: Sage Weil <sage@inktank.com>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>

net/ceph/messenger.c

@@ -3126,7 +3126,6 @@ struct ceph_msg *ceph_msg_new(int type, int front_len, gfp_t flags,
 	INIT_LIST_HEAD(&m->data);
 
 	/* front */
-	m->front_alloc_len = front_len;
 	if (front_len) {
 		if (front_len > PAGE_CACHE_SIZE) {
 			m->front.iov_base = __vmalloc(front_len, flags,
@@ -3143,7 +3142,7 @@ struct ceph_msg *ceph_msg_new(int type, int front_len, gfp_t flags,
 	} else {
 		m->front.iov_base = NULL;
 	}
-	m->front.iov_len = front_len;
+	m->front_alloc_len = m->front.iov_len = front_len;
 
 	dout("ceph_msg_new %p front %d\n", m, front_len);
 	return m;

net/ceph/osd_client.c

@@ -2515,9 +2515,9 @@ static struct ceph_msg *get_reply(struct ceph_connection *con,
 		     req->r_reply, req->r_reply->con);
 	ceph_msg_revoke_incoming(req->r_reply);
 
-	if (front_len > req->r_reply->front.iov_len) {
+	if (front_len > req->r_reply->front_alloc_len) {
 		pr_warning("get_reply front %d > preallocated %d (%u#%llu)\n",
-			   front_len, (int)req->r_reply->front.iov_len,
+			   front_len, req->r_reply->front_alloc_len,
 			   (unsigned int)con->peer_name.type,
 			   le64_to_cpu(con->peer_name.num));
 		m = ceph_msg_new(CEPH_MSG_OSD_OPREPLY, front_len, GFP_NOFS,