With uuid=on, store a persistent uuid in xattr on the upper dir to
give the overlayfs instance a persistent identifier.
This also makes f_fsid persistent and more reliable for reporting
fid info in fanotify events.
uuid=on is not supported on non-upper overlayfs or with upper fs
that does not support xattrs.
Signed-off-by: Amir Goldstein <amir73il@xxxxxxxxx>
---
Documentation/filesystems/overlayfs.rst | 3 ++
fs/overlayfs/overlayfs.h | 3 ++
fs/overlayfs/params.c | 5 ++++
fs/overlayfs/super.c | 10 +++++--
fs/overlayfs/util.c | 39 +++++++++++++++++++++++++
5 files changed, 57 insertions(+), 3 deletions(-)
diff --git a/Documentation/filesystems/overlayfs.rst b/Documentation/filesystems/overlayfs.rst
index d55381d3fa0f..8275ed735f77 100644
--- a/Documentation/filesystems/overlayfs.rst
+++ b/Documentation/filesystems/overlayfs.rst
@@ -671,6 +671,9 @@ controlled by the "uuid" mount option, which supports these values:
UUID of underlying layers is ignored.
- "on":
UUID of overlayfs is generated and used to report a unique fsid.
+ UUID is stored in xattr "trusted.overlay.uuid", making overlayfs fsid
+ unique and persistent. This option requires an overlayfs with upper
+ filesystem that supports xattrs.
Volatile mount
diff --git a/fs/overlayfs/overlayfs.h b/fs/overlayfs/overlayfs.h
index 000dd89fe319..8b026d758eaf 100644
--- a/fs/overlayfs/overlayfs.h
+++ b/fs/overlayfs/overlayfs.h
@@ -37,6 +37,7 @@ enum ovl_xattr {
OVL_XATTR_IMPURE,
OVL_XATTR_NLINK,
OVL_XATTR_UPPER,
+ OVL_XATTR_UUID,
OVL_XATTR_METACOPY,
OVL_XATTR_PROTATTR,
};
@@ -465,6 +466,8 @@ bool ovl_already_copied_up(struct dentry *dentry, int flags);
bool ovl_path_check_dir_xattr(struct ovl_fs *ofs, const struct path *path,
enum ovl_xattr ox);
bool ovl_path_check_origin_xattr(struct ovl_fs *ofs, const struct path *path);
+bool ovl_init_uuid_xattr(struct super_block *sb, struct ovl_fs *ofs,
+ const struct path *upperpath);
static inline bool ovl_check_origin_xattr(struct ovl_fs *ofs,
struct dentry *upperdentry)
diff --git a/fs/overlayfs/params.c b/fs/overlayfs/params.c
index 1ff93467e793..5a59c87c1dfe 100644
--- a/fs/overlayfs/params.c
+++ b/fs/overlayfs/params.c
@@ -801,6 +801,11 @@ int ovl_fs_params_verify(const struct ovl_fs_context *ctx,
config->ovl_volatile = false;
}
+ if (!config->upperdir && config->uuid == OVL_UUID_ON) {
+ pr_info("option \"uuid=on\" requires an upper fs, falling back to uuid=null.\n");
+ config->uuid = OVL_UUID_NULL;
+ }
+
/* Resolve verity -> metacopy dependency */
if (config->verity_mode && !config->metacopy) {
/* Don't allow explicit specified conflicting combinations */
diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
index 9c937bc85194..6cb8a8180702 100644
--- a/fs/overlayfs/super.c
+++ b/fs/overlayfs/super.c
@@ -777,6 +777,10 @@ static int ovl_make_workdir(struct super_block *sb, struct ovl_fs *ofs,
ofs->config.index = false;
pr_warn("...falling back to index=off.\n");
}
+ if (ovl_has_fsid(ofs)) {
+ ofs->config.uuid = OVL_UUID_NULL;
+ pr_warn("...falling back to uuid=null.\n");
+ }
/*
* xattr support is required for persistent st_ino.
* Without persistent st_ino, xino=auto falls back to xino=off.
@@ -1427,9 +1431,9 @@ int ovl_fill_super(struct super_block *sb, struct fs_context *fc)
if (!ovl_origin_uuid(ofs) && ofs->numfs > 1) {
pr_warn("The uuid=off requires a single fs for lower and upper, falling back to uuid=null.\n");
ofs->config.uuid = OVL_UUID_NULL;
- } else if (ovl_has_fsid(ofs)) {
- /* Use per instance uuid/fsid */
- uuid_gen(&sb->s_uuid);
+ } else if (ovl_has_fsid(ofs) && ovl_upper_mnt(ofs)) {
+ /* Use per instance persistent uuid/fsid */
+ ovl_init_uuid_xattr(sb, ofs, &ctx->upper);
}
if (!ovl_force_readonly(ofs) && ofs->config.index) {
diff --git a/fs/overlayfs/util.c b/fs/overlayfs/util.c
index 500133f196d7..8602982ae579 100644
--- a/fs/overlayfs/util.c
+++ b/fs/overlayfs/util.c
@@ -676,6 +676,43 @@ bool ovl_path_check_origin_xattr(struct ovl_fs *ofs, const struct path *path)
return false;
}
+/*
+ * Load persistent uuid from xattr into s_uuid if found, or store a new
+ * random generated value in s_uuid and in xattr.
+ */
+bool ovl_init_uuid_xattr(struct super_block *sb, struct ovl_fs *ofs,
+ const struct path *upperpath)
+{
+ bool set = false;
+ int res;
+
+ /* Try to load existing persistent uuid */
+ res = ovl_path_getxattr(ofs, upperpath, OVL_XATTR_UUID, sb->s_uuid.b,
+ UUID_SIZE);
+ if (res == UUID_SIZE)
+ return true;
+
+ if (res != -ENODATA)
+ goto fail;
+
+ /* Generate overlay instance uuid */
+ uuid_gen(&sb->s_uuid);
+
+ /* Try to store persistent uuid */
+ set = true;
+ res = ovl_setxattr(ofs, upperpath->dentry, OVL_XATTR_UUID, sb->s_uuid.b,
+ UUID_SIZE);
+ if (res == 0)
+ return true;
+
+fail:
+ memset(sb->s_uuid.b, 0, UUID_SIZE);
+ ofs->config.uuid = OVL_UUID_NULL;
+ pr_warn("failed to %s uuid (%pd2, err=%i); falling back to uuid=null.\n",
+ set ? "set" : "get", upperpath->dentry, res);
+ return false;
+}
+
bool ovl_path_check_dir_xattr(struct ovl_fs *ofs, const struct path *path,
enum ovl_xattr ox)
{
@@ -698,6 +735,7 @@ bool ovl_path_check_dir_xattr(struct ovl_fs *ofs, const struct path *path,
#define OVL_XATTR_IMPURE_POSTFIX "impure"
#define OVL_XATTR_NLINK_POSTFIX "nlink"
#define OVL_XATTR_UPPER_POSTFIX "upper"
+#define OVL_XATTR_UUID_POSTFIX "uuid"
#define OVL_XATTR_METACOPY_POSTFIX "metacopy"
#define OVL_XATTR_PROTATTR_POSTFIX "protattr"
@@ -712,6 +750,7 @@ const char *const ovl_xattr_table[][2] = {
OVL_XATTR_TAB_ENTRY(OVL_XATTR_IMPURE),
OVL_XATTR_TAB_ENTRY(OVL_XATTR_NLINK),
OVL_XATTR_TAB_ENTRY(OVL_XATTR_UPPER),
+ OVL_XATTR_TAB_ENTRY(OVL_XATTR_UUID),
OVL_XATTR_TAB_ENTRY(OVL_XATTR_METACOPY),
OVL_XATTR_TAB_ENTRY(OVL_XATTR_PROTATTR),
};
--
2.34.1
