SUNRPC: Always match an upcall message in gss_pipe_downcall()

It used to be possible for an rpc.gssd daemon to stuff the RPC credential
cache for any rpc client simply by creating RPCSEC_GSS contexts and then
doing downcalls. In practice, no daemons ever made use of this feature.

Remove this feature now, since it will be impossible to figure out which
mechanism a given context actually matches if we enable more
than one gss mechanism to use the same upcall pipe.

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

1 files changed, 27 insertions, 31 deletions

diff --git a/net/sunrpc/auth_gss/auth_gss.c b/net/sunrpc/auth_gss/auth_gss.c
index 653d712a1ffb..e407a352440f 100644
--- a/net/sunrpc/auth_gss/auth_gss.c
+++ b/net/sunrpc/auth_gss/auth_gss.c
@@ -306,8 +306,6 @@ gss_add_msg(struct gss_auth *gss_auth, struct gss_upcall_msg *gss_msg)
 static void
 __gss_unhash_msg(struct gss_upcall_msg *gss_msg)
 {
-        if (list_empty(&gss_msg->list))
-                return;
         list_del_init(&gss_msg->list);
         rpc_wake_up_status(&gss_msg->rpc_waitqueue, gss_msg->msg.errno);
         wake_up_all(&gss_msg->waitqueue);
@@ -320,8 +318,11 @@ gss_unhash_msg(struct gss_upcall_msg *gss_msg)
         struct gss_auth *gss_auth = gss_msg->auth;
         struct inode *inode = gss_auth->dentry->d_inode;
 
+        if (list_empty(&gss_msg->list))
+                return;
         spin_lock(&inode->i_lock);
-        __gss_unhash_msg(gss_msg);
+        if (!list_empty(&gss_msg->list))
+                __gss_unhash_msg(gss_msg);
         spin_unlock(&inode->i_lock);
 }
 
@@ -493,12 +494,11 @@ gss_pipe_downcall(struct file *filp, const char __user *src, size_t mlen)
         void *buf;
         struct rpc_clnt *clnt;
         struct gss_auth *gss_auth;
-        struct rpc_cred *cred;
         struct gss_upcall_msg *gss_msg;
         struct inode *inode = filp->f_path.dentry->d_inode;
         struct gss_cl_ctx *ctx;
         uid_t uid;
-        int err = -EFBIG;
+        ssize_t err = -EFBIG;
 
         if (mlen > MSG_BUF_MAXSIZE)
                 goto out;
@@ -523,43 +523,39 @@ gss_pipe_downcall(struct file *filp, const char __user *src, size_t mlen)
         ctx = gss_alloc_context();
         if (ctx == NULL)
                 goto err;
-        err = 0;
+
+        err = -ENOENT;
+        /* Find a matching upcall */
         gss_auth = container_of(clnt->cl_auth, struct gss_auth, rpc_auth);
+        spin_lock(&inode->i_lock);
+        gss_msg = __gss_find_upcall(gss_auth, uid);
+        if (gss_msg == NULL) {
+                spin_unlock(&inode->i_lock);
+                goto err_put_ctx;
+        }
+        list_del_init(&gss_msg->list);
+        spin_unlock(&inode->i_lock);
+
         p = gss_fill_context(p, end, ctx, gss_auth->mech);
         if (IS_ERR(p)) {
                 err = PTR_ERR(p);
-                if (err != -EACCES)
-                        goto err_put_ctx;
+                gss_msg->msg.errno = (err == -EACCES) ? -EACCES : -EAGAIN;
+                goto err_release_msg;
         }
+        gss_msg->ctx = gss_get_ctx(ctx);
+        err = mlen;
+
+err_release_msg:
         spin_lock(&inode->i_lock);
-        gss_msg = __gss_find_upcall(gss_auth, uid);
-        if (gss_msg) {
-                if (err == 0 && gss_msg->ctx == NULL)
-                        gss_msg->ctx = gss_get_ctx(ctx);
-                gss_msg->msg.errno = err;
-                __gss_unhash_msg(gss_msg);
-                spin_unlock(&inode->i_lock);
-                gss_release_msg(gss_msg);
-        } else {
-                struct auth_cred acred = { .uid = uid };
-                spin_unlock(&inode->i_lock);
-                cred = rpcauth_lookup_credcache(clnt->cl_auth, &acred, RPCAUTH_LOOKUP_NEW);
-                if (IS_ERR(cred)) {
-                        err = PTR_ERR(cred);
-                        goto err_put_ctx;
-                }
-                gss_cred_set_ctx(cred, gss_get_ctx(ctx));
-        }
-        gss_put_ctx(ctx);
-        kfree(buf);
-        dprintk("RPC:       gss_pipe_downcall returning length %Zu\n", mlen);
-        return mlen;
+        __gss_unhash_msg(gss_msg);
+        spin_unlock(&inode->i_lock);
+        gss_release_msg(gss_msg);
 err_put_ctx:
         gss_put_ctx(ctx);
 err:
         kfree(buf);
 out:
-        dprintk("RPC:       gss_pipe_downcall returning %d\n", err);
+        dprintk("RPC:       gss_pipe_downcall returning %Zd\n", err);
         return err;
 }