ovl: take mnt_want_write() for removing impure xattr

The optimization in ovl_cache_get_impure() that tries to remove an
unneeded "impure" xattr needs to take mnt_want_write() on upper fs.

Fixes: 4edb83bb1041 ("ovl: constant d_ino for non-merge dirs")
Cc: <stable@vger.kernel.org> #v4.14
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

diff --git a/fs/overlayfs/readdir.c b/fs/overlayfs/readdir.c
index 7dfe381..1a8c398 100644 (file)
--- a/fs/overlayfs/readdir.c
+++ b/fs/overlayfs/readdir.c
@@ -593,8 +593,15 @@ static struct ovl_dir_cache *ovl_cache_get_impure(struct path *path)
                return ERR_PTR(res);
        }
        if (list_empty(&cache->entries)) {
-               /* Good oportunity to get rid of an unnecessary "impure" flag */
-               ovl_do_removexattr(ovl_dentry_upper(dentry), OVL_XATTR_IMPURE);
+               /*
+                * A good opportunity to get rid of an unneeded "impure" flag.
+                * Removing the "impure" xattr is best effort.
+                */
+               if (!ovl_want_write(dentry)) {
+                       ovl_do_removexattr(ovl_dentry_upper(dentry),
+                                          OVL_XATTR_IMPURE);
+                       ovl_drop_write(dentry);
+               }
                ovl_clear_flag(OVL_IMPURE, d_inode(dentry));
                kfree(cache);
                return NULL;