diff --git a/Documentation/filesystems/overlayfs.txt b/Documentation/filesystems/overlayfs.txt
index 213547cb6d361b3513b2b7be6f99d508827bd747..7a05329844d2302075a16aa9b50a371e5ce7e099 100644
--- a/Documentation/filesystems/overlayfs.txt
+++ b/Documentation/filesystems/overlayfs.txt
@@ -190,6 +190,24 @@ Mount options:
Redirects are not created and not followed (equivalent to "redirect_dir=off"
if "redirect_always_follow" feature is not enabled).
+When the NFS export feature is enabled, every copied up directory is
+indexed by the file handle of the lower inode and a file handle of the
+upper directory is stored in a "trusted.overlay.upper" extended attribute
+on the index entry. On lookup of a merged directory, if the upper
+directory does not match the file handle stores in the index, that is an
+indication that multiple upper directories may be redirected to the same
+lower directory. In that case, lookup returns an error and warns about
+a possible inconsistency.
+
+Because lower layer redirects cannot be verified with the index, enabling
+NFS export support on an overlay filesystem with no upper layer requires
+turning off redirect follow (e.g. "redirect_dir=nofollow").
+
+When the NFS export feature is enabled, all directory index entries are
+verified on mount time to check that upper file handles are not stale.
+This verification may cause significant overhead in some cases.
+
+
Non-directories
---------------
@@ -299,6 +317,23 @@ filesystem are not allowed. If the underlying filesystem is changed,
the behavior of the overlay is undefined, though it will not result in
a crash or deadlock.
+When the overlay NFS export feature is enabled, overlay filesystems
+behavior on offline changes of the underlying lower layer is different
+than the behavior when NFS export is disabled.
+
+On every copy_up, an NFS file handle of the lower inode, along with the
+UUID of the lower filesystem, are encoded and stored in an extended
+attribute "trusted.overlay.origin" on the upper inode.
+
+When the NFS export feature is enabled, a lookup of a merged directory,
+that found a lower directory at the lookup path or at the path pointed
+to by the "trusted.overlay.redirect" extended attribute, will verify
+that the found lower directory file handle and lower filesystem UUID
+match the origin file handle that was stored at copy_up time. If a
+found lower directory does not match the stored origin, that directory
+will not be merged with the upper directory.
+
+
Testsuite
---------
diff --git a/fs/overlayfs/Kconfig b/fs/overlayfs/Kconfig
index 9eac01c3e21efb0a01721c1ade51f07a73c6e257..406e72de88f6f893a4e81189e6b8e1a9751573ae 100644
--- a/fs/overlayfs/Kconfig
+++ b/fs/overlayfs/Kconfig
@@ -50,3 +50,25 @@ config OVERLAY_FS_INDEX
Note, that the inodes index feature is not backward compatible.
That is, mounting an overlay which has an inodes index on a kernel
that doesn't support this feature will have unexpected results.
+
+config OVERLAY_FS_NFS_EXPORT
+ bool "Overlayfs: turn on NFS export feature by default"
+ depends on OVERLAY_FS
+ depends on OVERLAY_FS_INDEX
+ help
+ If this config option is enabled then overlay filesystems will use
+ the inodes index dir to decode overlay NFS file handles by default.
+ In this case, it is still possible to turn off NFS export support
+ globally with the "nfs_export=off" module option or on a filesystem
+ instance basis with the "nfs_export=off" mount option.
+
+ The NFS export feature creates an index on copy up of every file and
+ directory. This full index is used to detect overlay filesystems
+ inconsistencies on lookup, like redirect from multiple upper dirs to
+ the same lower dir. The full index may incur some overhead on mount
+ time, especially when verifying that directory file handles are not
+ stale.
+
+ Note, that the NFS export feature is not backward compatible.
+ That is, mounting an overlay which has a full index on a kernel
+ that doesn't support this feature will have unexpected results.
diff --git a/fs/overlayfs/overlayfs.h b/fs/overlayfs/overlayfs.h
index 1d62b1e6111a5441f4023e90efbf48a75712944e..db75955f96775951e5911699d62d02613a634806 100644
--- a/fs/overlayfs/overlayfs.h
+++ b/fs/overlayfs/overlayfs.h
@@ -194,6 +194,8 @@ const struct cred *ovl_override_creds(struct super_block *sb);
struct super_block *ovl_same_sb(struct super_block *sb);
bool ovl_can_decode_fh(struct super_block *sb);
struct dentry *ovl_indexdir(struct super_block *sb);
+bool ovl_index_all(struct super_block *sb);
+bool ovl_verify_lower(struct super_block *sb);
struct ovl_entry *ovl_alloc_entry(unsigned int numlower);
bool ovl_dentry_remote(struct dentry *dentry);
bool ovl_dentry_weird(struct dentry *dentry);
diff --git a/fs/overlayfs/ovl_entry.h b/fs/overlayfs/ovl_entry.h
index 608e487550708cec32e7a8ea4fe9b743351ab50c..6dd60fcf8cb71d677625c4c3bb9d8bc3224ceeeb 100644
--- a/fs/overlayfs/ovl_entry.h
+++ b/fs/overlayfs/ovl_entry.h
@@ -17,6 +17,7 @@ struct ovl_config {
bool redirect_follow;
const char *redirect_mode;
bool index;
+ bool nfs_export;
};
struct ovl_layer {
diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
index 4ebbb368fce8b87373527307583e2f3d36308068..1d538be87fa05861f828e22a58a51bbcba5eb914 100644
--- a/fs/overlayfs/super.c
+++ b/fs/overlayfs/super.c
@@ -45,6 +45,11 @@ module_param_named(index, ovl_index_def, bool, 0644);
MODULE_PARM_DESC(ovl_index_def,
"Default to on or off for the inodes index feature");
+static bool ovl_nfs_export_def = IS_ENABLED(CONFIG_OVERLAY_FS_NFS_EXPORT);
+module_param_named(nfs_export, ovl_nfs_export_def, bool, 0644);
+MODULE_PARM_DESC(ovl_nfs_export_def,
+ "Default to on or off for the NFS export feature");
+
static void ovl_entry_stack_free(struct ovl_entry *oe)
{
unsigned int i;
@@ -342,6 +347,9 @@ static int ovl_show_options(struct seq_file *m, struct dentry *dentry)
seq_printf(m, ",redirect_dir=%s", ofs->config.redirect_mode);
if (ofs->config.index != ovl_index_def)
seq_printf(m, ",index=%s", ofs->config.index ? "on" : "off");
+ if (ofs->config.nfs_export != ovl_nfs_export_def)
+ seq_printf(m, ",nfs_export=%s", ofs->config.nfs_export ?
+ "on" : "off");
return 0;
}
@@ -374,6 +382,8 @@ enum {
OPT_REDIRECT_DIR,
OPT_INDEX_ON,
OPT_INDEX_OFF,
+ OPT_NFS_EXPORT_ON,
+ OPT_NFS_EXPORT_OFF,
OPT_ERR,
};
@@ -385,6 +395,8 @@ static const match_table_t ovl_tokens = {
{OPT_REDIRECT_DIR, "redirect_dir=%s"},
{OPT_INDEX_ON, "index=on"},
{OPT_INDEX_OFF, "index=off"},
+ {OPT_NFS_EXPORT_ON, "nfs_export=on"},
+ {OPT_NFS_EXPORT_OFF, "nfs_export=off"},
{OPT_ERR, NULL}
};
@@ -491,6 +503,14 @@ static int ovl_parse_opt(char *opt, struct ovl_config *config)
config->index = false;
break;
+ case OPT_NFS_EXPORT_ON:
+ config->nfs_export = true;
+ break;
+
+ case OPT_NFS_EXPORT_OFF:
+ config->nfs_export = false;
+ break;
+
default:
pr_err("overlayfs: unrecognized mount option \"%s\" or missing value\n", p);
return -EINVAL;
@@ -696,13 +716,16 @@ static int ovl_lower_dir(const char *name, struct path *path,
*remote = true;
/*
- * The inodes index feature needs to encode and decode file
- * handles, so it requires that all layers support them.
+ * The inodes index feature and NFS export need to encode and decode
+ * file handles, so they require that all layers support them.
*/
- if (ofs->config.index && ofs->config.upperdir &&
+ if ((ofs->config.nfs_export ||
+ (ofs->config.index && ofs->config.upperdir)) &&
!ovl_can_decode_fh(path->dentry->d_sb)) {
ofs->config.index = false;
- pr_warn("overlayfs: fs on '%s' does not support file handles, falling back to index=off.\n", name);
+ ofs->config.nfs_export = false;
+ pr_warn("overlayfs: fs on '%s' does not support file handles, falling back to index=off,nfs_export=off.\n",
+ name);
}
return 0;
@@ -983,6 +1006,12 @@ static int ovl_make_workdir(struct ovl_fs *ofs, struct path *workpath)
pr_warn("overlayfs: upper fs does not support file handles, falling back to index=off.\n");
}
+ /* NFS export of r/w mount depends on index */
+ if (ofs->config.nfs_export && !ofs->config.index) {
+ pr_warn("overlayfs: NFS export requires \"index=on\", falling back to nfs_export=off.\n");
+ ofs->config.nfs_export = false;
+ }
+
out:
mnt_drop_write(mnt);
return err;
@@ -1141,6 +1170,10 @@ static struct ovl_entry *ovl_get_lowerstack(struct super_block *sb,
} else if (!ofs->config.upperdir && stacklen == 1) {
pr_err("overlayfs: at least 2 lowerdir are needed while upperdir nonexistent\n");
goto out_err;
+ } else if (!ofs->config.upperdir && ofs->config.nfs_export &&
+ ofs->config.redirect_follow) {
+ pr_warn("overlayfs: NFS export requires \"redirect_dir=nofollow\" on non-upper mount, falling back to nfs_export=off.\n");
+ ofs->config.nfs_export = false;
}
err = -ENOMEM;
@@ -1217,6 +1250,7 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent)
goto out_err;
ofs->config.index = ovl_index_def;
+ ofs->config.nfs_export = ovl_nfs_export_def;
err = ovl_parse_opt((char *) data, &ofs->config);
if (err)
goto out_err;
@@ -1277,8 +1311,13 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent)
}
/* Show index=off in /proc/mounts for forced r/o mount */
- if (!ofs->indexdir)
+ if (!ofs->indexdir) {
ofs->config.index = false;
+ if (ofs->upper_mnt && ofs->config.nfs_export) {
+ pr_warn("overlayfs: NFS export requires an index dir, falling back to nfs_export=off.\n");
+ ofs->config.nfs_export = false;
+ }
+ }
/* Never override disk quota limits or use reserved space */
cap_lower(cred->cap_effective, CAP_SYS_RESOURCE);
diff --git a/fs/overlayfs/util.c b/fs/overlayfs/util.c
index 06119f34a69da74c24a1e36b839032bd81ceda45..ae81d878248e69eab7228e0d8a931e895f4b3981 100644
--- a/fs/overlayfs/util.c
+++ b/fs/overlayfs/util.c
@@ -63,6 +63,22 @@ struct dentry *ovl_indexdir(struct super_block *sb)
return ofs->indexdir;
}
+/* Index all files on copy up. For now only enabled for NFS export */
+bool ovl_index_all(struct super_block *sb)
+{
+ struct ovl_fs *ofs = sb->s_fs_info;
+
+ return ofs->config.nfs_export && ofs->config.index;
+}
+
+/* Verify lower origin on lookup. For now only enabled for NFS export */
+bool ovl_verify_lower(struct super_block *sb)
+{
+ struct ovl_fs *ofs = sb->s_fs_info;
+
+ return ofs->config.nfs_export && ofs->config.index;
+}
+
struct ovl_entry *ovl_alloc_entry(unsigned int numlower)
{
size_t size = offsetof(struct ovl_entry, lowerstack[numlower]);