NFS: abort nfs_atomic_open_v23 if name is too long.

An attempt to open a file with a name longer than NFS3_MAXNAMLEN will
trigger a WARN_ON_ONCE in encode_filename3() because
nfs_atomic_open_v23() doesn't have the test on ->d_name.len that
nfs_atomic_open() has.

So add that test.

Reported-by: James Clark <[email protected]>
Closes: https://lore.kernel.org/all/[email protected]/
Fixes: 7c6c524 ("NFS: add atomic_open for NFSv3 to handle O_TRUNC correctly.")
Signed-off-by: NeilBrown <[email protected]>
Reviewed-by: Christoph Hellwig <[email protected]>
Signed-off-by: Trond Myklebust <[email protected]>

Author: neilbrown

fs/nfs/dir.c

@@ -2254,6 +2254,9 @@ int nfs_atomic_open_v23(struct inode *dir, struct dentry *dentry,
 	 */
 	int error = 0;
 
+	if (dentry->d_name.len > NFS_SERVER(dir)->namelen)
+		return -ENAMETOOLONG;
+
 	if (open_flags & O_CREAT) {
 		file->f_mode |= FMODE_CREATED;
 		error = nfs_do_create(dir, dentry, mode, open_flags);