[PATCH 6/6] ovl: Handle verity during copy-up

[Alexander Larsson <alexl@xxxxxxxxxx>]

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   | 27 +++++++++++++++++++++++++++
 fs/overlayfs/overlayfs.h |  2 ++
 fs/overlayfs/util.c      | 36 ++++++++++++++++++++++++++++++++++++
 3 files changed, 65 insertions(+)

diff --git a/fs/overlayfs/copy_up.c b/fs/overlayfs/copy_up.c
index eb266fb68730..a5c3862911d1 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)
@@ -644,6 +645,18 @@ 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;
 	}
@@ -919,6 +932,15 @@ 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.verity_require) {
+		struct dentry *lowerdata = ovl_dentry_lowerdata(dentry);
+
+		if (WARN_ON_ONCE(lowerdata == NULL) ||
+		    !fsverity_get_info(d_inode(lowerdata)))
+			return false;
+	}
+
 	return true;
 }
 
@@ -985,6 +1007,11 @@ 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)
+		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 b1d639ccd5ac..710dd816518f 100644
--- a/fs/overlayfs/overlayfs.h
+++ b/fs/overlayfs/overlayfs.h
@@ -473,6 +473,8 @@ int ovl_get_verity_xattr(struct ovl_fs *ofs, const struct path *path,
 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 55e90aa0978a..2bd9c9e68bf4 100644
--- a/fs/overlayfs/util.c
+++ b/fs/overlayfs/util.c
@@ -1285,6 +1285,42 @@ 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[FS_VERITY_MAX_DIGEST_SIZE];
+	enum hash_algo verity_algo;
+
+	if (!ofs->config.verity_generate || !S_ISREG(d_inode(dst)->i_mode))
+		return 0;
+
+	err = -EIO;
+	if (src) {
+		err = ovl_ensure_verity_loaded(ofs, 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, &verity_algo);
+	}
+	if (err == -ENODATA) {
+		if (ofs->config.verity_require) {
+			pr_warn_ratelimited("lower file '%pd' has no fs-verity digest\n",
+					    src->dentry);
+			return -EIO;
+		}
+		return 0;
+	}
+	if (err < 0)
+		return err;
+
+	return ovl_check_setxattr(ofs, dst, OVL_XATTR_VERITY,
+				  src_digest, hash_digest_size[verity_algo], -EOPNOTSUPP);
+}
+
 /*
  * ovl_sync_status() - Check fs sync status for volatile mounts
  *
-- 
2.39.2