Under the right circumstances, xenconsoled will corrupt its internal

list of domains causing a SEGV.  This is usually characterized by a 
rapid number of creations/destructions.  The attached patch fixes this.

1) Fix uninitialized next pointer.  This could sometimes cause xenconsoled to
   SEGV on an invalid domain pointer
2) Fix race condition in iterating domain list where removing a domain in a
   callback could lead to the iterators becoming invalid.

Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>

1 files changed, 20 insertions, 5 deletions

diff --git a/tools/console/daemon/io.c b/tools/console/daemon/io.c
index 87c3cc06e6..f334458e55 100644
--- a/tools/console/daemon/io.c
+++ b/tools/console/daemon/io.c
@@ -87,6 +87,7 @@ struct domain
 {
 	int domid;
 	int tty_fd;
+	bool is_dead;
 	struct buffer buffer;
 	struct domain *next;
 };
@@ -156,10 +157,12 @@ static struct domain *create_domain(int domid)
 
 	dom->domid = domid;
 	dom->tty_fd = domain_create_tty(dom);
+	dom->is_dead = false;
 	dom->buffer.data = 0;
 	dom->buffer.size = 0;
 	dom->buffer.capacity = 0;
 	dom->buffer.max_capacity = 0;
+	dom->next = 0;
 
 	dolog(LOG_DEBUG, "New domain %d", domid);
 
@@ -206,6 +209,16 @@ static void remove_domain(struct domain *dom)
 	}
 }
 
+static void remove_dead_domains(struct domain *dom)
+{
+	if (dom == NULL) return;
+	remove_dead_domains(dom->next);
+
+	if (dom->is_dead) {
+		remove_domain(dom);
+	}
+}
+
 static void handle_tty_read(struct domain *dom)
 {
 	ssize_t len;
@@ -224,7 +237,7 @@ static void handle_tty_read(struct domain *dom)
 		if (domain_is_valid(dom->domid)) {
 			dom->tty_fd = domain_create_tty(dom);
 		} else {
-			remove_domain(dom);
+			dom->is_dead = true;
 		}
 	} else if (domain_is_valid(dom->domid)) {
 		msg.u.control.msg.length = len;
@@ -235,7 +248,7 @@ static void handle_tty_read(struct domain *dom)
 		}
 	} else {
 		close(dom->tty_fd);
-		remove_domain(dom);
+		dom->is_dead = true;
 	}
 }
 
@@ -250,7 +263,7 @@ static void handle_tty_write(struct domain *dom)
 		if (domain_is_valid(dom->domid)) {
 			dom->tty_fd = domain_create_tty(dom);
 		} else {
-			remove_domain(dom);
+			dom->is_dead = true;
 		}
 	} else {
 		buffer_advance(&dom->buffer, len);
@@ -333,13 +346,15 @@ void handle_io(void)
 		}
 
 		for (d = dom_head; d; d = d->next) {
-			if (FD_ISSET(d->tty_fd, &readfds)) {
+			if (!d->is_dead && FD_ISSET(d->tty_fd, &readfds)) {
 				handle_tty_read(d);
 			}
 
-			if (FD_ISSET(d->tty_fd, &writefds)) {
+			if (!d->is_dead && FD_ISSET(d->tty_fd, &writefds)) {
 				handle_tty_write(d);
 			}
 		}
+
+		remove_dead_domains(dom_head);
 	} while (ret > -1);
 }