[PATCH] Fix race corrupting rpc upcall list

["J. Bruce Fields" <bfields@fieldses.org>]

From: J. Bruce Fields <bfields@redhat.com>

If rpc_queue_upcall() adds a new upcall to the rpci->pipe list just
after rpc_pipe_release calls rpc_purge_list(), but before it calls
gss_pipe_release (as rpci->ops->release_pipe(inode)), then the latter
will free a message without deleting it from the rpci->pipe list.

We will be left with a freed object on the rpc->pipe list.  Most
frequent symptoms are kernel crashes in rpc.gssd system calls on the
pipe in question.

We could just add a list_del(&gss_msg->msg.list) here.  But I can see no
reason for doing all this cleanup here; the preceding rpc_purge_list()
should have done the job, except possibly for any newly queued upcalls
as above, which can safely be left to wait for another opener.

Signed-off-by: J. Bruce Fields <bfields@redhat.com>
---

diff --git a/net/sunrpc/auth_gss/auth_gss.c b/net/sunrpc/auth_gss/auth_gss.c
index 36eee66..8ad9a34 100644
--- a/net/sunrpc/auth_gss/auth_gss.c
+++ b/net/sunrpc/auth_gss/auth_gss.c
@@ -744,23 +744,6 @@ static int gss_pipe_open_v1(struct inode *inode)
 static void
 gss_pipe_release(struct inode *inode)
 {
-	struct rpc_inode *rpci = RPC_I(inode);
-	struct gss_upcall_msg *gss_msg;
-
-	spin_lock(&inode->i_lock);
-	while (!list_empty(&rpci->in_downcall)) {
-
-		gss_msg = list_entry(rpci->in_downcall.next,
-				struct gss_upcall_msg, list);
-		gss_msg->msg.errno = -EPIPE;
-		atomic_inc(&gss_msg->count);
-		__gss_unhash_msg(gss_msg);
-		spin_unlock(&inode->i_lock);
-		gss_release_msg(gss_msg);
-		spin_lock(&inode->i_lock);
-	}
-	spin_unlock(&inode->i_lock);
-
 	put_pipe_version();
 }