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Diffstat (limited to 'fs/overlayfs/export.c')
-rw-r--r--fs/overlayfs/export.c210
1 files changed, 166 insertions, 44 deletions
diff --git a/fs/overlayfs/export.c b/fs/overlayfs/export.c
index bb94ce9da5c8..9df455ca59a8 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;