On Wed, Jun 21, 2023 at 2:18 PM Alexander Larsson <alexl@xxxxxxxxxx> wrote:
>
> Historically overlay.metacopy was a zero-size xattr, and it's
> existence marked a metacopy file. This change adds a versioned header
> with a flag field, a length and a digest. The initial use-case of this
> will be for validating a fs-verity digest, but the flags field could
> also be used later for other new features.
>
> ovl_check_metacopy_xattr() now returns the size of the xattr,
> emulating a size of OVL_METACOPY_MIN_SIZE for empty xattrs to
> distinguish it from the no-xattr case.
>
> Signed-off-by: Alexander Larsson <alexl@xxxxxxxxxx>
Looks good.
Reviewed-by: Amir Goldstein <amir73il@xxxxxxxxx>
> ---
> fs/overlayfs/namei.c | 10 +++++-----
> fs/overlayfs/overlayfs.h | 24 +++++++++++++++++++++++-
> fs/overlayfs/util.c | 37 +++++++++++++++++++++++++++++++++----
> 3 files changed, 61 insertions(+), 10 deletions(-)
>
> diff --git a/fs/overlayfs/namei.c b/fs/overlayfs/namei.c
> index 57adf911735f..3dd480253710 100644
> --- a/fs/overlayfs/namei.c
> +++ b/fs/overlayfs/namei.c
> @@ -25,7 +25,7 @@ struct ovl_lookup_data {
> bool stop;
> bool last;
> char *redirect;
> - bool metacopy;
> + int metacopy;
> /* Referring to last redirect xattr */
> bool absolute_redirect;
> };
> @@ -270,7 +270,7 @@ static int ovl_lookup_single(struct dentry *base, struct ovl_lookup_data *d,
> d->stop = true;
> goto put_and_out;
> }
> - err = ovl_check_metacopy_xattr(OVL_FS(d->sb), &path);
> + err = ovl_check_metacopy_xattr(OVL_FS(d->sb), &path, NULL);
> if (err < 0)
> goto out_err;
>
> @@ -963,7 +963,7 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
> .stop = false,
> .last = ovl_redirect_follow(ofs) ? false : !ovl_numlower(poe),
> .redirect = NULL,
> - .metacopy = false,
> + .metacopy = 0,
> };
>
> if (dentry->d_name.len > ofs->namelen)
> @@ -1120,7 +1120,7 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
>
> /* Defer lookup of lowerdata in data-only layers to first access */
> if (d.metacopy && ctr && ofs->numdatalayer && d.absolute_redirect) {
> - d.metacopy = false;
> + d.metacopy = 0;
> ctr++;
> }
>
> @@ -1211,7 +1211,7 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
> upperredirect = NULL;
> goto out_free_oe;
> }
> - err = ovl_check_metacopy_xattr(ofs, &upperpath);
> + err = ovl_check_metacopy_xattr(ofs, &upperpath, NULL);
> if (err < 0)
> goto out_free_oe;
> uppermetacopy = err;
> diff --git a/fs/overlayfs/overlayfs.h b/fs/overlayfs/overlayfs.h
> index cf92a9aaf934..6d4e08df0dfe 100644
> --- a/fs/overlayfs/overlayfs.h
> +++ b/fs/overlayfs/overlayfs.h
> @@ -7,6 +7,7 @@
> #include <linux/kernel.h>
> #include <linux/uuid.h>
> #include <linux/fs.h>
> +#include <linux/fsverity.h>
> #include <linux/namei.h>
> #include <linux/posix_acl.h>
> #include <linux/posix_acl_xattr.h>
> @@ -140,6 +141,26 @@ struct ovl_fh {
> #define OVL_FH_FID_OFFSET (OVL_FH_WIRE_OFFSET + \
> offsetof(struct ovl_fb, fid))
>
> +/* On-disk format for "metacopy" xattr (if non-zero size) */
> +struct ovl_metacopy {
> + u8 version; /* 0 */
> + u8 len; /* size of this header + used digest bytes */
> + u8 flags;
> + u8 digest_algo; /* FS_VERITY_HASH_ALG_* constant, 0 for no digest */
> + u8 digest[FS_VERITY_MAX_DIGEST_SIZE]; /* Only the used part on disk */
> +} __packed;
> +
> +#define OVL_METACOPY_MAX_SIZE (sizeof(struct ovl_metacopy))
> +#define OVL_METACOPY_MIN_SIZE (OVL_METACOPY_MAX_SIZE - FS_VERITY_MAX_DIGEST_SIZE)
> +#define OVL_METACOPY_INIT { 0, OVL_METACOPY_MIN_SIZE }
> +
> +static inline int ovl_metadata_digest_size(const struct ovl_metacopy *metacopy)
> +{
> + if (metacopy->len < OVL_METACOPY_MIN_SIZE)
> + return 0;
> + return (int)metacopy->len - OVL_METACOPY_MIN_SIZE;
> +}
> +
> extern const char *const ovl_xattr_table[][2];
> static inline const char *ovl_xattr(struct ovl_fs *ofs, enum ovl_xattr ox)
> {
> @@ -490,7 +511,8 @@ bool ovl_need_index(struct dentry *dentry);
> int ovl_nlink_start(struct dentry *dentry);
> void ovl_nlink_end(struct dentry *dentry);
> int ovl_lock_rename_workdir(struct dentry *workdir, struct dentry *upperdir);
> -int ovl_check_metacopy_xattr(struct ovl_fs *ofs, const struct path *path);
> +int ovl_check_metacopy_xattr(struct ovl_fs *ofs, const struct path *path,
> + struct ovl_metacopy *data);
> bool ovl_is_metacopy_dentry(struct dentry *dentry);
> char *ovl_get_redirect_xattr(struct ovl_fs *ofs, const struct path *path, int padding);
> int ovl_sync_status(struct ovl_fs *ofs);
> diff --git a/fs/overlayfs/util.c b/fs/overlayfs/util.c
> index 7ef9e13c404a..921747223991 100644
> --- a/fs/overlayfs/util.c
> +++ b/fs/overlayfs/util.c
> @@ -1054,8 +1054,12 @@ int ovl_lock_rename_workdir(struct dentry *workdir, struct dentry *upperdir)
> return -EIO;
> }
>
> -/* err < 0, 0 if no metacopy xattr, 1 if metacopy xattr found */
> -int ovl_check_metacopy_xattr(struct ovl_fs *ofs, const struct path *path)
> +/*
> + * err < 0, 0 if no metacopy xattr, metacopy data size if xattr found.
> + * an empty xattr returns OVL_METACOPY_MIN_SIZE to distinguish from no xattr value.
> + */
> +int ovl_check_metacopy_xattr(struct ovl_fs *ofs, const struct path *path,
> + struct ovl_metacopy *data)
> {
> int res;
>
> @@ -1063,7 +1067,8 @@ int ovl_check_metacopy_xattr(struct ovl_fs *ofs, const struct path *path)
> if (!S_ISREG(d_inode(path->dentry)->i_mode))
> return 0;
>
> - res = ovl_path_getxattr(ofs, path, OVL_XATTR_METACOPY, NULL, 0);
> + res = ovl_path_getxattr(ofs, path, OVL_XATTR_METACOPY,
> + data, data ? OVL_METACOPY_MAX_SIZE : 0);
> if (res < 0) {
> if (res == -ENODATA || res == -EOPNOTSUPP)
> return 0;
> @@ -1077,7 +1082,31 @@ int ovl_check_metacopy_xattr(struct ovl_fs *ofs, const struct path *path)
> goto out;
> }
>
> - return 1;
> + if (res == 0) {
> + /* Emulate empty data for zero size metacopy xattr */
> + res = OVL_METACOPY_MIN_SIZE;
> + if (data) {
> + memset(data, 0, res);
> + data->len = res;
> + }
> + } else if (res < OVL_METACOPY_MIN_SIZE) {
> + pr_warn_ratelimited("metacopy file '%pd' has too small xattr\n",
> + path->dentry);
> + return -EIO;
> + } else if (data) {
> + if (data->version != 0) {
> + pr_warn_ratelimited("metacopy file '%pd' has unsupported version\n",
> + path->dentry);
> + return -EIO;
> + }
> + if (res != data->len) {
> + pr_warn_ratelimited("metacopy file '%pd' has invalid xattr size\n",
> + path->dentry);
> + return -EIO;
> + }
> + }
> +
> + return res;
> out:
> pr_warn_ratelimited("failed to get metacopy (%i)\n", res);
> return res;
> --
> 2.40.1
>
