ovl: implement lookup in data-only layers

Lookup in data-only layers only for a lower metacopy with an absolute
redirect xattr.

The metacopy xattr is not checked on files found in the data-only layers
and redirect xattr are not followed in the data-only layers.

Reviewed-by: Alexander Larsson <alexl@redhat.com>
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

diff --git a/fs/overlayfs/namei.c b/fs/overlayfs/namei.c
index 5c1b0397c8ce545391843c773bb279f131614dbf..517f31a28f725daad28d2a9eb4656b0d2869d074 100644 (file)
--- a/fs/overlayfs/namei.c
+++ b/fs/overlayfs/namei.c
@@ -14,6 +14,8 @@
 #include <linux/exportfs.h>
 #include "overlayfs.h"
 
+#include "../internal.h"       /* for vfs_path_lookup */
+
 struct ovl_lookup_data {
        struct super_block *sb;
        struct vfsmount *mnt;
@@ -24,6 +26,8 @@ struct ovl_lookup_data {
        bool last;
        char *redirect;
        bool metacopy;
+       /* Referring to last redirect xattr */
+       bool absolute_redirect;
 };
 
 static int ovl_check_redirect(const struct path *path, struct ovl_lookup_data *d,
@@ -33,11 +37,13 @@ static int ovl_check_redirect(const struct path *path, struct ovl_lookup_data *d
        char *buf;
        struct ovl_fs *ofs = OVL_FS(d->sb);
 
+       d->absolute_redirect = false;
        buf = ovl_get_redirect_xattr(ofs, path, prelen + strlen(post));
        if (IS_ERR_OR_NULL(buf))
                return PTR_ERR(buf);
 
        if (buf[0] == '/') {
+               d->absolute_redirect = true;
                /*
                 * One of the ancestor path elements in an absolute path
                 * lookup in ovl_lookup_layer() could have been opaque and
@@ -349,6 +355,61 @@ static int ovl_lookup_layer(struct dentry *base, struct ovl_lookup_data *d,
        return 0;
 }
 
+static int ovl_lookup_data_layer(struct dentry *dentry, const char *redirect,
+                                const struct ovl_layer *layer,
+                                struct path *datapath)
+{
+       int err;
+
+       err = vfs_path_lookup(layer->mnt->mnt_root, layer->mnt, redirect,
+                       LOOKUP_BENEATH | LOOKUP_NO_SYMLINKS | LOOKUP_NO_XDEV,
+                       datapath);
+       pr_debug("lookup lowerdata (%pd2, redirect=\"%s\", layer=%d, err=%i)\n",
+                dentry, redirect, layer->idx, err);
+
+       if (err)
+               return err;
+
+       err = -EREMOTE;
+       if (ovl_dentry_weird(datapath->dentry))
+               goto out_path_put;
+
+       err = -ENOENT;
+       /* Only regular file is acceptable as lower data */
+       if (!d_is_reg(datapath->dentry))
+               goto out_path_put;
+
+       return 0;
+
+out_path_put:
+       path_put(datapath);
+
+       return err;
+}
+
+/* Lookup in data-only layers by absolute redirect to layer root */
+static int ovl_lookup_data_layers(struct dentry *dentry, const char *redirect,
+                                 struct ovl_path *lowerdata)
+{
+       struct ovl_fs *ofs = OVL_FS(dentry->d_sb);
+       const struct ovl_layer *layer;
+       struct path datapath;
+       int err = -ENOENT;
+       int i;
+
+       layer = &ofs->layers[ofs->numlayer - ofs->numdatalayer];
+       for (i = 0; i < ofs->numdatalayer; i++, layer++) {
+               err = ovl_lookup_data_layer(dentry, redirect, layer, &datapath);
+               if (!err) {
+                       mntput(datapath.mnt);
+                       lowerdata->dentry = datapath.dentry;
+                       lowerdata->layer = layer;
+                       return 0;
+               }
+       }
+
+       return err;
+}
 
 int ovl_check_origin_fh(struct ovl_fs *ofs, struct ovl_fh *fh, bool connected,
                        struct dentry *upperdentry, struct ovl_path **stackp)
@@ -917,7 +978,7 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
 
                if (!ofs->config.redirect_follow)
                        d.last = i == ovl_numlower(poe) - 1;
-               else
+               else if (d.is_dir || !ofs->numdatalayer)
                        d.last = lower.layer->idx == ovl_numlower(roe);
 
                d.mnt = lower.layer->mnt;
@@ -1011,6 +1072,16 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
                }
        }
 
+       /* Lookup absolute redirect from lower metacopy in data-only layers */
+       if (d.metacopy && ctr && ofs->numdatalayer && d.absolute_redirect) {
+               err = ovl_lookup_data_layers(dentry, d.redirect,
+                                            &stack[ctr]);
+               if (!err) {
+                       d.metacopy = false;
+                       ctr++;
+               }
+       }
+
        /*
         * For regular non-metacopy upper dentries, there is no lower
         * path based lookup, hence ctr will be zero. If a dentry is found