From: Stefan Metzmacher <metze@samba.org>
Date: Wed, 7 Aug 2024 15:01:53 +0000 (+0200)
Subject: s3:smbd: let mkdir_internal() try VFS_RENAME_HOW_NO_REPLACE first
X-Git-Tag: tdb-1.4.13~1310
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=1bacaae5261b157f0dc4efb68fdc82d4cf387eb9;p=thirdparty%2Fsamba.git

s3:smbd: let mkdir_internal() try VFS_RENAME_HOW_NO_REPLACE first

With renameat2(RENAME_NOREPLACE) being available
it's even better, as we don't even have the short
window where the incomplete directory is visible
to others.

The flow will be this:

tmp_name = ".::TMPNAME:D:$PID:client_name"
mkdirat(tmp_name, mode=client_mode);
prepare_acls(tmp_name);
renameat2(tmp_name, client_name, NOREPLACE);
if (EEXIST) {
   unlinkat(tmp_name);
   return EEXIST;
}
if (EINVAL) {
   /* fallback if NOREPLACE is not supported */
   mkdirat(client_name, mode=0);
   if (EEXIST) {
      unlinkat(tmp_name);
      return EEXIST;
   }
   renameat(tmp_name, client_name);
}

BUG: https://bugzilla.samba.org/show_bug.cgi?id=15693

Signed-off-by: Stefan Metzmacher <metze@samba.org>
Reviewed-by: Ralph Boehme <slow@samba.org>
---

diff --git a/source3/smbd/open.c b/source3/smbd/open.c
index cba43d1a1cd..a1c1c259e5c 100644
--- a/source3/smbd/open.c
+++ b/source3/smbd/open.c
@@ -4681,7 +4681,7 @@ static NTSTATUS mkdir_internal(connection_struct *conn,
 	struct server_id_buf idbuf;
 	char *idstr = server_id_str_buf_unique_ex(id, '%', &idbuf);
 	struct vfs_open_how how = { .flags = O_RDONLY|O_DIRECTORY, };
-	struct vfs_rename_how rhow = { .flags = 0, };
+	struct vfs_rename_how rhow = { .flags = VFS_RENAME_HOW_NO_REPLACE, };
 	int ret;
 
 	if (!CAN_WRITE(conn) || (access_mask & ~(conn->share_access))) {
@@ -4896,7 +4896,27 @@ mkdir_first:
 	 */
 	tmp_atname->st = smb_dname->st;
 
-	{
+	/*
+	 * We first try VFS_RENAME_HOW_NO_REPLACE,
+	 * if it's implemented in the kernel,
+	 * we'll always get EEXIST if the target
+	 * exist, as it's handled at the linux vfs
+	 * layer. But if it doesn't exist we
+	 * can still get EINVAL if the actual
+	 * filesystem doesn't support RENAME_NOREPLACE.
+	 *
+	 * If the kernel doesn't support rename2()
+	 * we get EINVAL instead of ENOSYS (this
+	 * is mapped in the libreplace replacement
+	 * (as well as the glibc replacement).
+	 */
+	ret = SMB_VFS_RENAMEAT(conn,
+			       parent_dir_fname->fsp,
+			       tmp_atname,
+			       parent_dir_fname->fsp,
+			       smb_fname_atname,
+			       &rhow);
+	if (ret == -1 && errno == EINVAL) {
 		/*
 		 * This is the strategie we use without having
 		 * renameat2(RENAME_NOREPLACE):
@@ -4916,6 +4936,8 @@ mkdir_first:
 		 * the incomplete directory, which has a mode of 0.
 		 */
 
+		rhow.flags &= ~VFS_RENAME_HOW_NO_REPLACE;
+
 		DBG_DEBUG("MKDIRAT/RENAMEAT '%s' -> '%s'\n",
 			  tmp_dname, orig_dname);