Commit d9544c1b authored by Amir Goldstein's avatar Amir Goldstein
Browse files

ovl: store persistent uuid/fsid with uuid=on 



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: default avatarAmir Goldstein <amir73il@gmail.com>
parent b0504bfe

Documentation/filesystems/overlayfs.rst

+3 −0
Original line number Diff line number Diff line
@@ -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

fs/overlayfs/overlayfs.h

+3 −0
Original line number Diff line number Diff line
@@ -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)

fs/overlayfs/params.c

+5 −0
Original line number Diff line number Diff line
@@ -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 */

fs/overlayfs/super.c

+7 −3
Original line number Diff line number Diff line
@@ -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) {

fs/overlayfs/util.c

+39 −0
Original line number Diff line number Diff line
@@ -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),

};