On Mon, Jun 12, 2023 at 1:29 PM Alexander Larsson <alexl@xxxxxxxxxx> wrote:
>
> During regular metacopy, if lowerdata file has fs-verity enabled,
> set the new overlay.verity xattr (if enabled).
>
> During real data copy up, remove any old overlay.verity xattr.
>
> If verity is required, and lowerdata does not have fs-verity enabled,
> fall back to full copy-up (or the generated metacopy would not validate).
>
> Signed-off-by: Alexander Larsson <alexl@xxxxxxxxxx>
> ---
> fs/overlayfs/copy_up.c | 31 +++++++++++++++++++++++++++++++
> fs/overlayfs/overlayfs.h | 3 +++
> fs/overlayfs/util.c | 39 ++++++++++++++++++++++++++++++++++++++-
> 3 files changed, 72 insertions(+), 1 deletion(-)
>
> diff --git a/fs/overlayfs/copy_up.c b/fs/overlayfs/copy_up.c
> index 68f01fd7f211..67c4f14c694c 100644
> --- a/fs/overlayfs/copy_up.c
> +++ b/fs/overlayfs/copy_up.c
> @@ -19,6 +19,7 @@
> #include <linux/fdtable.h>
> #include <linux/ratelimit.h>
> #include <linux/exportfs.h>
> +#include <linux/fsverity.h>
> #include "overlayfs.h"
>
> #define OVL_COPY_UP_CHUNK_SIZE (1 << 20)
> @@ -643,6 +644,18 @@ static int ovl_copy_up_metadata(struct ovl_copy_up_ctx *c, struct dentry *temp)
> if (c->metacopy) {
> err = ovl_check_setxattr(ofs, temp, OVL_XATTR_METACOPY,
> NULL, 0, -EOPNOTSUPP);
> +
> + /* Copy the verity digest if any so we can validate the copy-up later */
> + if (!err) {
> + struct path lowerdatapath;
> +
> + ovl_path_lowerdata(c->dentry, &lowerdatapath);
> + if (WARN_ON_ONCE(lowerdatapath.dentry == NULL))
> + err = -EIO;
> + else
> + err = ovl_set_verity_xattr_from(ofs, temp, &lowerdatapath);
> + }
> +
> if (err)
> return err;
> }
> @@ -918,6 +931,19 @@ static bool ovl_need_meta_copy_up(struct dentry *dentry, umode_t mode,
> if (flags && ((OPEN_FMODE(flags) & FMODE_WRITE) || (flags & O_TRUNC)))
> return false;
>
> + /* Fall back to full copy if no fsverity on source data and we require verity */
> + if (ofs->config.require_verity) {
> + struct path lowerdata;
> +
> + ovl_path_lowerdata(dentry, &lowerdata);
> +
> + if (WARN_ON_ONCE(lowerdata.dentry == NULL) ||
> + ovl_ensure_verity_loaded(&lowerdata) ||
> + !fsverity_get_info(d_inode(lowerdata.dentry))) {
> + return false;
> + }
> + }
> +
> return true;
> }
>
> @@ -984,6 +1010,11 @@ static int ovl_copy_up_meta_inode_data(struct ovl_copy_up_ctx *c)
> if (err)
> goto out_free;
>
> + err = ovl_removexattr(ofs, upperpath.dentry, OVL_XATTR_VERITY);
> + if (err && err != -ENODATA)
-EOPNOTSUPP is also not a failure, although you could do:
if (!ofs->noxattr) ...
to avoid this error
> + goto out_free;
> +
> + err = 0;
> ovl_set_upperdata(d_inode(c->dentry));
> out_free:
> kfree(capability);
> diff --git a/fs/overlayfs/overlayfs.h b/fs/overlayfs/overlayfs.h
> index 66e3f79ed6d0..472bef93cb0b 100644
> --- a/fs/overlayfs/overlayfs.h
> +++ b/fs/overlayfs/overlayfs.h
> @@ -462,11 +462,14 @@ int ovl_lock_rename_workdir(struct dentry *workdir, struct dentry *upperdir);
> int ovl_check_metacopy_xattr(struct ovl_fs *ofs, const struct path *path);
> 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_ensure_verity_loaded(struct path *path);
> int ovl_get_verity_xattr(struct ovl_fs *ofs, const struct path *path,
> u8 *digest_buf, int *buf_length);
> int ovl_validate_verity(struct ovl_fs *ofs,
> struct path *metapath,
> struct path *datapath);
> +int ovl_set_verity_xattr_from(struct ovl_fs *ofs, struct dentry *dst,
> + struct path *src);
> int ovl_sync_status(struct ovl_fs *ofs);
>
> static inline void ovl_set_flag(unsigned long flag, struct inode *inode)
> diff --git a/fs/overlayfs/util.c b/fs/overlayfs/util.c
> index a4666ba3d5a3..cef907ff66bc 100644
> --- a/fs/overlayfs/util.c
> +++ b/fs/overlayfs/util.c
> @@ -1174,7 +1174,7 @@ int ovl_get_verity_xattr(struct ovl_fs *ofs, const struct path *path,
> }
>
> /* Call with mounter creds as it may open the file */
> -static int ovl_ensure_verity_loaded(struct path *datapath)
> +int ovl_ensure_verity_loaded(struct path *datapath)
> {
> struct inode *inode = d_inode(datapath->dentry);
> const struct fsverity_info *vi;
> @@ -1248,6 +1248,43 @@ int ovl_validate_verity(struct ovl_fs *ofs,
> return 0;
> }
>
> +int ovl_set_verity_xattr_from(struct ovl_fs *ofs, struct dentry *dst,
> + struct path *src)
> +{
> + int err;
> + u8 src_digest[1+FS_VERITY_MAX_DIGEST_SIZE];
> + enum hash_algo verity_algo;
> +
> + if (!ofs->config.verity || !S_ISREG(d_inode(dst)->i_mode))
> + return 0;
> +
> + err = -EIO;
> + if (src) {
> + err = ovl_ensure_verity_loaded(src);
> + if (err < 0) {
> + pr_warn_ratelimited("lower file '%pd' failed to load fs-verity info\n",
> + src->dentry);
> + return -EIO;
> + }
> +
> + err = fsverity_get_digest(d_inode(src->dentry), src_digest + 1, &verity_algo);
> + }
> + if (err == -ENODATA) {
> + if (ofs->config.require_verity) {
> + pr_warn_ratelimited("lower file '%pd' has no fs-verity digest\n",
> + src->dentry);
> + return -EIO;
> + }
> + return 0;
> + }
> + if (err < 0)
> + return err;
> +
> + src_digest[0] = (u8)verity_algo;
> + return ovl_check_setxattr(ofs, dst, OVL_XATTR_VERITY,
> + src_digest, 1 + hash_digest_size[verity_algo], -EOPNOTSUPP);
> +}
> +
> /*
> * ovl_sync_status() - Check fs sync status for volatile mounts
> *
> --
> 2.40.1
>
