From 9610adf7abf9bfb31c69b093e72321c54af35629 Mon Sep 17 00:00:00 2001
From: Akihiko Odaki <odaki@rsg.ci.i.u-tokyo.ac.jp>
Date: Wed, 29 May 2024 16:24:21 +0900
Subject: [PATCH] main: Do not set -1 for owner overriding xattrs

ovl_setattr () used to pass -1 as uid or gid when either of them
is not changed for do_fchown () / do_chown (), but if these functions
use overriding xattrs instead of real fchown () or chown (), it causes
-1 to be written in owner overriding xattrs and break them.

Replace -1 with the current uid or gid before calling do_fchown () /
do_chown ().

Signed-off-by: Akihiko Odaki <odaki@rsg.ci.i.u-tokyo.ac.jp>
---
 main.c          | 18 ++++++++++++++++++
 tests/unpriv.sh | 18 ++++++++++++++++++
 2 files changed, 36 insertions(+)

diff --git a/main.c b/main.c
index fc5cc79..5bd1993 100644
--- a/main.c
+++ b/main.c
@@ -4158,6 +4158,24 @@ ovl_setattr (fuse_req_t req, fuse_ino_t ino, struct stat *attr, int to_set, stru
 
   if (uid != -1 || gid != -1)
     {
+      struct stat st;
+
+      if (do_stat (node, fd, NULL, &st) < 0)
+        {
+          fuse_reply_err (req, errno);
+          return;
+        }
+
+      if (uid == -1)
+        {
+          uid = st.st_uid;
+        }
+
+      if (gid == -1)
+        {
+          gid = st.st_gid;
+        }
+
       if (fd >= 0)
         ret = do_fchown (lo, fd, uid, gid, node->ino->mode);
       else
diff --git a/tests/unpriv.sh b/tests/unpriv.sh
index 7bb19ed..3ce252e 100755
--- a/tests/unpriv.sh
+++ b/tests/unpriv.sh
@@ -29,3 +29,21 @@ else
 fi
 
 fusermount -u merged || [ $? -eq "${EXPECT_UMOUNT_STATUS:-0}" ]
+
+# xattr_permissions=2
+rm -rf lower upper workdir merged
+mkdir lower upper workdir merged
+
+touch upper/file
+
+fuse-overlayfs -o lowerdir=lower,upperdir=upper,workdir=workdir,xattr_permissions=2 merged
+
+# Ensure UID is preserved with chgrp.
+podman unshare chgrp 1 merged/file
+test $(podman unshare stat -c %u:%g merged/file) = 0:1
+
+# Ensure UID and GID are preserved with chmod.
+chmod 600 merged/file
+test $(podman unshare stat -c %u:%g merged/file) = 0:1
+
+fusermount -u merged || [ $? -eq "${EXPECT_UMOUNT_STATUS:-0}" ]