SUNRPC: Fix race corrupting rpc upcall

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

2 files changed, 8 insertions, 7 deletions

diff --git a/net/sunrpc/auth_gss/auth_gss.c b/net/sunrpc/auth_gss/auth_gss.c
index dcfc66bab2bb..12c485982814 100644
--- 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);
 
diff --git a/net/sunrpc/rpc_pipe.c b/net/sunrpc/rpc_pipe.c
index 95ccbcf45d3e..41a762f82630 100644
--- a/net/sunrpc/rpc_pipe.c
+++ b/net/sunrpc/rpc_pipe.c
@@ -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);
         }