From bf07089081a0ea18da4a103b9d813ffae3c2f6d8 Mon Sep 17 00:00:00 2001 From: Alexander Larsson Date: Wed, 21 Jun 2023 10:32:31 +0200 Subject: ovl: Add versioned header for overlay.metacopy xattr 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 Reviewed-by: Amir Goldstein Signed-off-by: Amir Goldstein --- fs/overlayfs/namei.c | 10 +++++----- fs/overlayfs/overlayfs.h | 24 +++++++++++++++++++++++- fs/overlayfs/util.c | 37 +++++++++++++++++++++++++++++++++---- 3 files changed, 61 insertions(+), 10 deletions(-) (limited to 'fs') 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 34cc72f8fb6a..2e659b355f61 100644 --- a/fs/overlayfs/overlayfs.h +++ b/fs/overlayfs/overlayfs.h @@ -7,6 +7,7 @@ #include #include #include +#include #include #include #include @@ -132,6 +133,26 @@ 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) { @@ -458,7 +479,8 @@ 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 @@ err: 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; -- cgit v1.2.3