linux-kernel - [112/129] SUNRPC: Fix race corrupting rpc upcall

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Date:	Sat, 18 Sep 2010 12:13:30 -0700
From:	Greg KH <gregkh@...e.de>
To:	linux-kernel@...r.kernel.org, stable@...nel.org
Cc:	stable-review@...nel.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, alan@...rguk.ukuu.org.uk,
	Trond Myklebust <Trond.Myklebust@...app.com>
Subject: [112/129] SUNRPC: Fix race corrupting rpc upcall

2.6.35-stable review patch.  If anyone has any objections, please let us know.

------------------

From: Trond Myklebust <Trond.Myklebust@...app.com>

commit 5a67657a2e90c9e4a48518f95d4ba7777aa20fbb upstream.

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.

Reported-by: J. Bruce Fields <bfields@...hat.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@...app.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>

---
 net/sunrpc/auth_gss/auth_gss.c |    9 +++++----
 net/sunrpc/rpc_pipe.c          |    6 +++---
 2 files changed, 8 insertions(+), 7 deletions(-)

--- a/net/sunrpc/auth_gss/auth_gss.c
+++ b/net/sunrpc/auth_gss/auth_gss.c
@@ -745,17 +745,18 @@ gss_pipe_release(struct inode *inode)
 	struct rpc_inode *rpci = RPC_I(inode);
 	struct gss_upcall_msg *gss_msg;
 
+restart:
 	spin_lock(&inode->i_lock);
-	while (!list_empty(&rpci->in_downcall)) {
+	list_for_each_entry(gss_msg, &rpci->in_downcall, list) {
 
-		gss_msg = list_entry(rpci->in_downcall.next,
-				struct gss_upcall_msg, list);
+		if (!list_empty(&gss_msg->msg.list))
+			continue;
 		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);
+		goto restart;
 	}
 	spin_unlock(&inode->i_lock);
 
--- a/net/sunrpc/rpc_pipe.c
+++ b/net/sunrpc/rpc_pipe.c
@@ -48,7 +48,7 @@ static void rpc_purge_list(struct rpc_in
 		return;
 	do {
 		msg = list_entry(head->next, struct rpc_pipe_msg, list);
-		list_del(&msg->list);
+		list_del_init(&msg->list);
 		msg->errno = err;
 		destroy_msg(msg);
 	} while (!list_empty(head));
@@ -208,7 +208,7 @@ rpc_pipe_release(struct inode *inode, st
 	if (msg != NULL) {
 		spin_lock(&inode->i_lock);
 		msg->errno = -EAGAIN;
-		list_del(&msg->list);
+		list_del_init(&msg->list);
 		spin_unlock(&inode->i_lock);
 		rpci->ops->destroy_msg(msg);
 	}
@@ -268,7 +268,7 @@ rpc_pipe_read(struct file *filp, char __
 	if (res < 0 || msg->len == msg->copied) {
 		filp->private_data = NULL;
 		spin_lock(&inode->i_lock);
-		list_del(&msg->list);
+		list_del_init(&msg->list);
 		spin_unlock(&inode->i_lock);
 		rpci->ops->destroy_msg(msg);
 	}


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