1 files changed, 169 insertions, 47 deletions

diff --git a/fs/overlayfs/export.c b/fs/overlayfs/export.c
index bb94ce9da5c8..87bd4148f4fb 100644
--- a/fs/overlayfs/export.c
+++ b/fs/overlayfs/export.c
@@ -19,6 +19,142 @@
 #include <linux/ratelimit.h>
 #include "overlayfs.h"
 
+static int ovl_encode_maybe_copy_up(struct dentry *dentry)
+{
+        int err;
+
+        if (ovl_dentry_upper(dentry))
+                return 0;
+
+        err = ovl_want_write(dentry);
+        if (!err) {
+                err = ovl_copy_up(dentry);
+                ovl_drop_write(dentry);
+        }
+
+        if (err) {
+                pr_warn_ratelimited("overlayfs: failed to copy up on encode (%pd2, err=%i)\n",
+                                    dentry, err);
+        }
+
+        return err;
+}
+
+/*
+ * Before encoding a non-upper directory file handle from real layer N, we need
+ * to check if it will be possible to reconnect an overlay dentry from the real
+ * lower decoded dentry. This is done by following the overlay ancestry up to a
+ * "layer N connected" ancestor and verifying that all parents along the way are
+ * "layer N connectable". If an ancestor that is NOT "layer N connectable" is
+ * found, we need to copy up an ancestor, which is "layer N connectable", thus
+ * making that ancestor "layer N connected". For example:
+ *
+ * layer 1: /a
+ * layer 2: /a/b/c
+ *
+ * The overlay dentry /a is NOT "layer 2 connectable", because if dir /a is
+ * copied up and renamed, upper dir /a will be indexed by lower dir /a from
+ * layer 1. The dir /a from layer 2 will never be indexed, so the algorithm (*)
+ * in ovl_lookup_real_ancestor() will not be able to lookup a connected overlay
+ * dentry from the connected lower dentry /a/b/c.
+ *
+ * To avoid this problem on decode time, we need to copy up an ancestor of
+ * /a/b/c, which is "layer 2 connectable", on encode time. That ancestor is
+ * /a/b. After copy up (and index) of /a/b, it will become "layer 2 connected"
+ * and when the time comes to decode the file handle from lower dentry /a/b/c,
+ * ovl_lookup_real_ancestor() will find the indexed ancestor /a/b and decoding
+ * a connected overlay dentry will be accomplished.
+ *
+ * (*) the algorithm in ovl_lookup_real_ancestor() can be improved to lookup an
+ * entry /a in the lower layers above layer N and find the indexed dir /a from
+ * layer 1. If that improvement is made, then the check for "layer N connected"
+ * will need to verify there are no redirects in lower layers above N. In the
+ * example above, /a will be "layer 2 connectable". However, if layer 2 dir /a
+ * is a target of a layer 1 redirect, then /a will NOT be "layer 2 connectable":
+ *
+ * layer 1: /A (redirect = /a)
+ * layer 2: /a/b/c
+ */
+
+/* Return the lowest layer for encoding a connectable file handle */
+static int ovl_connectable_layer(struct dentry *dentry)
+{
+        struct ovl_entry *oe = OVL_E(dentry);
+
+        /* We can get overlay root from root of any layer */
+        if (dentry == dentry->d_sb->s_root)
+                return oe->numlower;
+
+        /*
+         * If it's an unindexed merge dir, then it's not connectable with any
+         * lower layer
+         */
+        if (ovl_dentry_upper(dentry) &&
+            !ovl_test_flag(OVL_INDEX, d_inode(dentry)))
+                return 0;
+
+        /* We can get upper/overlay path from indexed/lower dentry */
+        return oe->lowerstack[0].layer->idx;
+}
+
+/*
+ * @dentry is "connected" if all ancestors up to root or a "connected" ancestor
+ * have the same uppermost lower layer as the origin's layer. We may need to
+ * copy up a "connectable" ancestor to make it "connected". A "connected" dentry
+ * cannot become non "connected", so cache positive result in dentry flags.
+ *
+ * Return the connected origin layer or < 0 on error.
+ */
+static int ovl_connect_layer(struct dentry *dentry)
+{
+        struct dentry *next, *parent = NULL;
+        int origin_layer;
+        int err = 0;
+
+        if (WARN_ON(dentry == dentry->d_sb->s_root) ||
+            WARN_ON(!ovl_dentry_lower(dentry)))
+                return -EIO;
+
+        origin_layer = OVL_E(dentry)->lowerstack[0].layer->idx;
+        if (ovl_dentry_test_flag(OVL_E_CONNECTED, dentry))
+                return origin_layer;
+
+        /* Find the topmost origin layer connectable ancestor of @dentry */
+        next = dget(dentry);
+        for (;;) {
+                parent = dget_parent(next);
+                if (WARN_ON(parent == next)) {
+                        err = -EIO;
+                        break;
+                }
+
+                /*
+                 * If @parent is not origin layer connectable, then copy up
+                 * @next which is origin layer connectable and we are done.
+                 */
+                if (ovl_connectable_layer(parent) < origin_layer) {
+                        err = ovl_encode_maybe_copy_up(next);
+                        break;
+                }
+
+                /* If @parent is connected or indexed we are done */
+                if (ovl_dentry_test_flag(OVL_E_CONNECTED, parent) ||
+                    ovl_test_flag(OVL_INDEX, d_inode(parent)))
+                        break;
+
+                dput(next);
+                next = parent;
+        }
+
+        dput(parent);
+        dput(next);
+
+        if (!err)
+                ovl_dentry_set_flag(OVL_E_CONNECTED, dentry);
+
+        return err ?: origin_layer;
+}
+
 /*
  * We only need to encode origin if there is a chance that the same object was
  * encoded pre copy up and then we need to stay consistent with the same
@@ -41,73 +177,59 @@
  * L = lower file handle
  *
  * (*) Connecting an overlay dir from real lower dentry is not always
- * possible when there are redirects in lower layers. To mitigate this case,
- * we copy up the lower dir first and then encode an upper dir file handle.
+ * possible when there are redirects in lower layers and non-indexed merge dirs.
+ * To mitigate those case, we may copy up the lower dir ancestor before encode
+ * a lower dir file handle.
+ *
+ * Return 0 for upper file handle, > 0 for lower file handle or < 0 on error.
  */
-static bool ovl_should_encode_origin(struct dentry *dentry)
+static int ovl_check_encode_origin(struct dentry *dentry)
 {
         struct ovl_fs *ofs = dentry->d_sb->s_fs_info;
 
+        /* Upper file handle for pure upper */
         if (!ovl_dentry_lower(dentry))
-                return false;
+                return 0;
 
         /*
-         * Decoding a merge dir, whose origin's parent is under a redirected
-         * lower dir is not always possible. As a simple aproximation, we do
-         * not encode lower dir file handles when overlay has multiple lower
-         * layers and origin is below the topmost lower layer.
+         * Upper file handle for non-indexed upper.
          *
-         * TODO: copy up only the parent that is under redirected lower.
+         * Root is never indexed, so if there's an upper layer, encode upper for
+         * root.
          */
-        if (d_is_dir(dentry) && ofs->upper_mnt &&
-            OVL_E(dentry)->lowerstack[0].layer->idx > 1)
-                return false;
-
-        /* Decoding a non-indexed upper from origin is not implemented */
         if (ovl_dentry_upper(dentry) &&
             !ovl_test_flag(OVL_INDEX, d_inode(dentry)))
-                return false;
-
-        return true;
-}
-
-static int ovl_encode_maybe_copy_up(struct dentry *dentry)
-{
-        int err;
-
-        if (ovl_dentry_upper(dentry))
                 return 0;
 
-        err = ovl_want_write(dentry);
-        if (err)
-                return err;
-
-        err = ovl_copy_up(dentry);
+        /*
+         * Decoding a merge dir, whose origin's ancestor is under a redirected
+         * lower dir or under a non-indexed upper is not always possible.
+         * ovl_connect_layer() will try to make origin's layer "connected" by
+         * copying up a "connectable" ancestor.
+         */
+        if (d_is_dir(dentry) && ofs->upper_mnt)
+                return ovl_connect_layer(dentry);
 
-        ovl_drop_write(dentry);
-        return err;
+        /* Lower file handle for indexed and non-upper dir/non-dir */
+        return 1;
 }
 
 static int ovl_d_to_fh(struct dentry *dentry, char *buf, int buflen)
 {
-        struct dentry *origin = ovl_dentry_lower(dentry);
         struct ovl_fh *fh = NULL;
-        int err;
+        int err, enc_lower;
 
         /*
-         * If we should not encode a lower dir file handle, copy up and encode
-         * an upper dir file handle.
+         * Check if we should encode a lower or upper file handle and maybe
+         * copy up an ancestor to make lower file handle connectable.
          */
-        if (!ovl_should_encode_origin(dentry)) {
-                err = ovl_encode_maybe_copy_up(dentry);
-                if (err)
-                        goto fail;
-
-                origin = NULL;
-        }
+        err = enc_lower = ovl_check_encode_origin(dentry);
+        if (enc_lower < 0)
+                goto fail;
 
-        /* Encode an upper or origin file handle */
-        fh = ovl_encode_fh(origin ?: ovl_dentry_upper(dentry), !origin);
+        /* Encode an upper or lower file handle */
+        fh = ovl_encode_fh(enc_lower ? ovl_dentry_lower(dentry) :
+                                       ovl_dentry_upper(dentry), !enc_lower);
         err = PTR_ERR(fh);
         if (IS_ERR(fh))
                 goto fail;
@@ -355,8 +477,8 @@ static struct dentry *ovl_lookup_real_inode(struct super_block *sb,
                 dput(upper);
         }
 
-        if (!this)
-                return NULL;
+        if (IS_ERR_OR_NULL(this))
+                return this;
 
         if (WARN_ON(ovl_dentry_real_at(this, layer->idx) != real)) {
                 dput(this);
@@ -498,7 +620,7 @@ static struct dentry *ovl_lookup_real(struct super_block *sb,
                         if (err == -ECHILD) {
                                 this = ovl_lookup_real_ancestor(sb, real,
                                                                 layer);
-                                err = IS_ERR(this) ? PTR_ERR(this) : 0;
+                                err = PTR_ERR_OR_ZERO(this);
                         }
                         if (!err) {
                                 dput(connected);