From 6f2af48a03fb29ac6cb35cfee2c370f7ce8645ce Mon Sep 17 00:00:00 2001
From: Giuseppe Scrivano <gscrivan@redhat.com>
Date: Mon, 25 Jan 2021 19:00:08 +0100
Subject: [PATCH] main: check if whiteout device already exists

on newer kernels unprivileged users can create whiteout devices.  If
the whiteout device creation failed with EEXIST, check whether the
existing file is already a whiteout.

Closes: https://github.com/containers/fuse-overlayfs/issues/271

Signed-off-by: Giuseppe Scrivano <gscrivan@redhat.com>
---
 main.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/main.c b/main.c
index 3898e52..50afdf8 100644
--- a/main.c
+++ b/main.c
@@ -733,6 +733,21 @@ create_whiteout (struct ovl_data *lo, struct ovl_node *parent, const char *name,
       if (ret == 0)
         return 0;
 
+      if (errno == EEXIST)
+        {
+          int saved_errno = errno;
+          struct stat st;
+
+          /* Check whether it is already a whiteout.  */
+          if (TEMP_FAILURE_RETRY (fstatat (get_upper_layer (lo)->fd, whiteout_path, &st, AT_SYMLINK_NOFOLLOW)) == 0
+              && (st.st_mode & S_IFMT) == S_IFCHR
+              && major (st.st_rdev) == 0
+              && minor (st.st_rdev) == 0)
+            return 0;
+
+          errno = saved_errno;
+        }
+
       if (errno != EPERM && errno != ENOTSUP)
         return -1;