NFS: Fix use of copy_to_user() in idmap_pipe_upcall

The idmap_pipe_upcall() function expects the copy_to_user() function to
return a negative error value if the call fails, but copy_to_user()
returns an unsigned long number of bytes that couldn't be copied.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

1 files changed, 6 insertions, 8 deletions

diff --git a/fs/nfs/idmap.c b/fs/nfs/idmap.c
index c56fc7d5a46e..d93e071b900c 100644
--- a/fs/nfs/idmap.c
+++ b/fs/nfs/idmap.c
@@ -358,17 +358,15 @@ idmap_pipe_upcall(struct file *filp, struct rpc_pipe_msg *msg,
                   char __user *dst, size_t buflen)
 {
         char *data = (char *)msg->data + msg->copied;
-        ssize_t mlen = msg->len - msg->copied;
-        ssize_t left;
-
-        if (mlen > buflen)
-                mlen = buflen;
+        size_t mlen = min(msg->len, buflen);
+        unsigned long left;
 
         left = copy_to_user(dst, data, mlen);
-        if (left < 0) {
-                msg->errno = left;
-                return left;
+        if (left == mlen) {
+                msg->errno = -EFAULT;
+                return -EFAULT;
         }
+
         mlen -= left;
         msg->copied += mlen;
         msg->errno = 0;