ovl: fix filattr copy-up failure

This regression can be reproduced with ntfs-3g and overlayfs:

  mkdir lower upper work overlay
  dd if=/dev/zero of=ntfs.raw bs=1M count=2
  mkntfs -F ntfs.raw
  mount ntfs.raw lower
  touch lower/file.txt
  mount -t overlay -o lowerdir=lower,upperdir=upper,workdir=work - overlay
  mv overlay/file.txt overlay/file2.txt

mv fails and (misleadingly) prints

  mv: cannot move 'overlay/file.txt' to a subdirectory of itself, 'overlay/file2.txt'

The reason is that ovl_copy_fileattr() is triggered due to S_NOATIME being
set on all inodes (by fuse) regardless of fileattr.

ovl_copy_fileattr() tries to retrieve file attributes from lower file, but
that fails because filesystem does not support this ioctl (this should fail
with ENOTTY, but ntfs-3g return EINVAL instead).  This failure is
propagated to origial operation (in this case rename) that triggered the
copy-up.

The fix is to ignore ENOTTY and EINVAL errors from fileattr_get() in copy
up.  This also requires turning the internal ENOIOCTLCMD into ENOTTY.

As a further measure to prevent unnecessary failures, only try the
fileattr_get/set on upper if there are any flags to copy up.

Side note: a number of filesystems set S_NOATIME (and sometimes other inode
flags) irrespective of fileattr flags.  This causes unnecessary calls
during copy up, which might lead to a performance issue, especially if
latency is high.  To fix this, the kernel would need to differentiate
between the two cases.  E.g. introduce SB_NOATIME_UPDATE, a per-sb variant
of S_NOATIME.  SB_NOATIME doesn't work, because that's interpreted as
"filesystem doesn't store an atime attribute"

Reported-and-tested-by: Kevin Locke <kevin@kevinlocke.name>
Fixes: 72db821 ("ovl: copy up sync/noatime fileattr flags")
Cc: <stable@vger.kernel.org> # v5.15
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

fs/overlayfs/copy_up.c

@@ -140,12 +140,14 @@ static int ovl_copy_fileattr(struct inode *inode, struct path *old,
 	int err;
 
 	err = ovl_real_fileattr_get(old, &oldfa);
-	if (err)
-		return err;
-
-	err = ovl_real_fileattr_get(new, &newfa);
-	if (err)
+	if (err) {
+		/* Ntfs-3g returns -EINVAL for "no fileattr support" */
+		if (err == -ENOTTY || err == -EINVAL)
+			return 0;
+		pr_warn("failed to retrieve lower fileattr (%pd2, err=%i)\n",
+			old, err);
 		return err;
+	}
 
 	/*
 	 * We cannot set immutable and append-only flags on upper inode,
@@ -159,6 +161,17 @@ static int ovl_copy_fileattr(struct inode *inode, struct path *old,
 			return err;
 	}
 
+	/* Don't bother copying flags if none are set */
+	if (!(oldfa.flags & OVL_COPY_FS_FLAGS_MASK))
+		return 0;
+
+	err = ovl_real_fileattr_get(new, &newfa);
+	if (err) {
+		pr_warn("failed to retrieve upper fileattr (%pd2, err=%i)\n",
+			new, err);
+		return err;
+	}
+
 	BUILD_BUG_ON(OVL_COPY_FS_FLAGS_MASK & ~FS_COMMON_FL);
 	newfa.flags &= ~OVL_COPY_FS_FLAGS_MASK;
 	newfa.flags |= (oldfa.flags & OVL_COPY_FS_FLAGS_MASK);

fs/overlayfs/inode.c

@@ -610,7 +610,10 @@ int ovl_real_fileattr_get(struct path *realpath, struct fileattr *fa)
 	if (err)
 		return err;
 
-	return vfs_fileattr_get(realpath->dentry, fa);
+	err = vfs_fileattr_get(realpath->dentry, fa);
+	if (err == -ENOIOCTLCMD)
+		err = -ENOTTY;
+	return err;
 }
 
 int ovl_fileattr_get(struct dentry *dentry, struct fileattr *fa)