ubifs: xattr: Don't operate on deleted inodes

xattr operations can race with unlink and the following assert triggers:
UBIFS assert failed in ubifs_jnl_change_xattr at 1606 (pid 6256)

Fix this by checking i_nlink before working on the host inode.

Cc: <stable@vger.kernel.org>
Fixes: 1e51764a3c ("UBIFS: add new flash file system")
Signed-off-by: Richard Weinberger <richard@nod.at>

fs/ubifs/xattr.c

@@ -152,6 +152,12 @@ static int create_xattr(struct ubifs_info *c, struct inode *host,
 	ui->data_len = size;
 
 	mutex_lock(&host_ui->ui_mutex);
+
+	if (!host->i_nlink) {
+		err = -ENOENT;
+		goto out_noent;
+	}
+
 	host->i_ctime = current_time(host);
 	host_ui->xattr_cnt += 1;
 	host_ui->xattr_size += CALC_DENT_SIZE(fname_len(nm));
@@ -184,6 +190,7 @@ out_cancel:
 	host_ui->xattr_size -= CALC_XATTR_BYTES(size);
 	host_ui->xattr_names -= fname_len(nm);
 	host_ui->flags &= ~UBIFS_CRYPT_FL;
+out_noent:
 	mutex_unlock(&host_ui->ui_mutex);
 out_free:
 	make_bad_inode(inode);
@@ -235,6 +242,12 @@ static int change_xattr(struct ubifs_info *c, struct inode *host,
 	mutex_unlock(&ui->ui_mutex);
 
 	mutex_lock(&host_ui->ui_mutex);
+
+	if (!host->i_nlink) {
+		err = -ENOENT;
+		goto out_noent;
+	}
+
 	host->i_ctime = current_time(host);
 	host_ui->xattr_size -= CALC_XATTR_BYTES(old_size);
 	host_ui->xattr_size += CALC_XATTR_BYTES(size);
@@ -256,6 +269,7 @@ static int change_xattr(struct ubifs_info *c, struct inode *host,
 out_cancel:
 	host_ui->xattr_size -= CALC_XATTR_BYTES(size);
 	host_ui->xattr_size += CALC_XATTR_BYTES(old_size);
+out_noent:
 	mutex_unlock(&host_ui->ui_mutex);
 	make_bad_inode(inode);
 out_free:
@@ -482,6 +496,12 @@ static int remove_xattr(struct ubifs_info *c, struct inode *host,
 		return err;
 
 	mutex_lock(&host_ui->ui_mutex);
+
+	if (!host->i_nlink) {
+		err = -ENOENT;
+		goto out_noent;
+	}
+
 	host->i_ctime = current_time(host);
 	host_ui->xattr_cnt -= 1;
 	host_ui->xattr_size -= CALC_DENT_SIZE(fname_len(nm));
@@ -501,6 +521,7 @@ out_cancel:
 	host_ui->xattr_size += CALC_DENT_SIZE(fname_len(nm));
 	host_ui->xattr_size += CALC_XATTR_BYTES(ui->data_len);
 	host_ui->xattr_names += fname_len(nm);
+out_noent:
 	mutex_unlock(&host_ui->ui_mutex);
 	ubifs_release_budget(c, &req);
 	make_bad_inode(inode);
@@ -540,6 +561,9 @@ static int ubifs_xattr_remove(struct inode *host, const char *name)
 
 	ubifs_assert(inode_is_locked(host));
 
+	if (!host->i_nlink)
+		return -ENOENT;
+
 	if (fname_len(&nm) > UBIFS_MAX_NLEN)
 		return -ENAMETOOLONG;