ovl: Do not lose security.capability xattr over metadata file copy-up

If a file has been copied up metadata only, and later data is copied up,
upper loses any security.capability xattr it has (underlying filesystem
clears it as upon file write).

From a user's point of view, this is just a file copy-up and that should
not result in losing security.capability xattr.  Hence, before data copy
up, save security.capability xattr (if any) and restore it on upper after
data copy up is complete.

Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
Reviewed-by: Amir Goldstein <amir73il@gmail.com>
Fixes: 0c2888749363 ("ovl: A new xattr OVL_XATTR_METACOPY for file on upper")
Cc: <stable@vger.kernel.org> # v4.19+
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

1 files changed, 26 insertions, 2 deletions

diff --git a/fs/overlayfs/copy_up.c b/fs/overlayfs/copy_up.c
index 48119b23375b..68b3303e4b46 100644
--- a/fs/overlayfs/copy_up.c
+++ b/fs/overlayfs/copy_up.c
@@ -742,6 +742,8 @@ static int ovl_copy_up_meta_inode_data(struct ovl_copy_up_ctx *c)
 {
 	struct path upperpath, datapath;
 	int err;
+	char *capability = NULL;
+	ssize_t uninitialized_var(cap_size);
 
 	ovl_path_upper(c->dentry, &upperpath);
 	if (WARN_ON(upperpath.dentry == NULL))
@@ -751,15 +753,37 @@ static int ovl_copy_up_meta_inode_data(struct ovl_copy_up_ctx *c)
 	if (WARN_ON(datapath.dentry == NULL))
 		return -EIO;
 
+	if (c->stat.size) {
+		err = cap_size = ovl_getxattr(upperpath.dentry, XATTR_NAME_CAPS,
+					      &capability, 0);
+		if (err < 0 && err != -ENODATA)
+			goto out;
+	}
+
 	err = ovl_copy_up_data(&datapath, &upperpath, c->stat.size);
 	if (err)
-		return err;
+		goto out_free;
+
+	/*
+	 * Writing to upper file will clear security.capability xattr. We
+	 * don't want that to happen for normal copy-up operation.
+	 */
+	if (capability) {
+		err = ovl_do_setxattr(upperpath.dentry, XATTR_NAME_CAPS,
+				      capability, cap_size, 0);
+		if (err)
+			goto out_free;
+	}
+
 
 	err = vfs_removexattr(upperpath.dentry, OVL_XATTR_METACOPY);
 	if (err)
-		return err;
+		goto out_free;
 
 	ovl_set_upperdata(d_inode(c->dentry));
+out_free:
+	kfree(capability);
+out:
 	return err;
 }