NFSv4: Fix an Oops in nfs4_do_setattr

commit 09a54f0e upstream.

If the user specifies an open mode of 3, then we don't have a NFSv4 state
attached to the context, and so we Oops when we try to dereference it.
Reported-by: Olga Kornievskaia <aglo@umich.edu>
Fixes: 29b59f94 ("NFSv4: change nfs4_do_setattr to take...")
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
Cc: stable@vger.kernel.org # v4.10: 991eedb1: NFSv4: Only pass the...
Cc: stable@vger.kernel.org # v4.10+
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

fs/nfs/nfs4proc.c

@@ -3133,7 +3133,7 @@ static int _nfs4_do_setattr(struct inode *inode,
 
 	if (nfs4_copy_delegation_stateid(inode, FMODE_WRITE, &arg->stateid, &delegation_cred)) {
 		/* Use that stateid */
-	} else if (ctx != NULL) {
+	} else if (ctx != NULL && ctx->state) {
 		struct nfs_lock_context *l_ctx;
 		if (!nfs4_valid_open_stateid(ctx->state))
 			return -EBADF;