nfsd: make a copy of struct iattr before calling notify_change

notify_change can modify the iattr structure. In particular it can
end up setting ATTR_MODE when ATTR_KILL_SUID is already set, causing
a BUG() if the same iattr is passed to notify_change more than once.

Make a copy of the struct iattr before calling notify_change.
Reported-by: Zhi Li <yieli@redhat.com>
Link: https://bugzilla.redhat.com/show_bug.cgi?id=2207969Tested-by: Zhi Li <yieli@redhat.com>
Fixes: 34b91dda ("NFSD: Make nfsd4_setattr() wait before returning NFS4ERR_DELAY")
Signed-off-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

fs/nfsd/vfs.c

@@ -536,7 +536,15 @@ nfsd_setattr(struct svc_rqst *rqstp, struct svc_fh *fhp,
 
 	inode_lock(inode);
 	for (retries = 1;;) {
-		host_err = __nfsd_setattr(dentry, iap);
+		struct iattr attrs;
+
+		/*
+		 * notify_change() can alter its iattr argument, making
+		 * @iap unsuitable for submission multiple times. Make a
+		 * copy for every loop iteration.
+		 */
+		attrs = *iap;
+		host_err = __nfsd_setattr(dentry, &attrs);
 		if (host_err != -EAGAIN || !retries--)
 			break;
 		if (!nfsd_wait_for_delegreturn(rqstp, inode))