SUNRPC: Fix race corrupting rpc upcall
Trond Myklebust [Sun, 12 Sep 2010 23:55:25 +0000 (19:55 -0400)]
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@redhat.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
Cc: stable@kernel.org

net/sunrpc/auth_gss/auth_gss.c
net/sunrpc/rpc_pipe.c

index dcfc66b..12c4859 100644 (file)
@@ -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);
 
index 95ccbcf..41a762f 100644 (file)
@@ -48,7 +48,7 @@ static void rpc_purge_list(struct rpc_inode *rpci, struct list_head *head,
                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, struct file *filp)
        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 __user *buf, size_t len, loff_t *offset)
        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);
        }