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, 35 insertions, 20 deletions

diff --git a/fs/overlayfs/util.c b/fs/overlayfs/util.c
index 7c01327b1852..4035e640f402 100644
--- a/fs/overlayfs/util.c
+++ b/fs/overlayfs/util.c
@@ -863,28 +863,49 @@ bool ovl_is_metacopy_dentry(struct dentry *dentry)
 	return (oe->numlower > 1);
 }
 
-char *ovl_get_redirect_xattr(struct dentry *dentry, int padding)
+ssize_t ovl_getxattr(struct dentry *dentry, char *name, char **value,
+		     size_t padding)
 {
-	int res;
-	char *s, *next, *buf = NULL;
+	ssize_t res;
+	char *buf = NULL;
 
-	res = vfs_getxattr(dentry, OVL_XATTR_REDIRECT, NULL, 0);
+	res = vfs_getxattr(dentry, name, NULL, 0);
 	if (res < 0) {
 		if (res == -ENODATA || res == -EOPNOTSUPP)
-			return NULL;
+			return -ENODATA;
 		goto fail;
 	}
 
-	buf = kzalloc(res + padding + 1, GFP_KERNEL);
-	if (!buf)
-		return ERR_PTR(-ENOMEM);
+	if (res != 0) {
+		buf = kzalloc(res + padding, GFP_KERNEL);
+		if (!buf)
+			return -ENOMEM;
 
-	if (res == 0)
-		goto invalid;
+		res = vfs_getxattr(dentry, name, buf, res);
+		if (res < 0)
+			goto fail;
+	}
+	*value = buf;
+
+	return res;
+
+fail:
+	pr_warn_ratelimited("overlayfs: failed to get xattr %s: err=%zi)\n",
+			    name, res);
+	kfree(buf);
+	return res;
+}
 
-	res = vfs_getxattr(dentry, OVL_XATTR_REDIRECT, buf, res);
+char *ovl_get_redirect_xattr(struct dentry *dentry, int padding)
+{
+	int res;
+	char *s, *next, *buf = NULL;
+
+	res = ovl_getxattr(dentry, OVL_XATTR_REDIRECT, &buf, padding + 1);
+	if (res == -ENODATA)
+		return NULL;
 	if (res < 0)
-		goto fail;
+		return ERR_PTR(res);
 	if (res == 0)
 		goto invalid;
 
@@ -900,15 +921,9 @@ char *ovl_get_redirect_xattr(struct dentry *dentry, int padding)
 	}
 
 	return buf;
-
-err_free:
-	kfree(buf);
-	return ERR_PTR(res);
-fail:
-	pr_warn_ratelimited("overlayfs: failed to get redirect (%i)\n", res);
-	goto err_free;
 invalid:
 	pr_warn_ratelimited("overlayfs: invalid redirect (%s)\n", buf);
 	res = -EINVAL;
-	goto err_free;
+	kfree(buf);
+	return ERR_PTR(res);
 }