s3/smbd: let non_widelink_open() chdir() to directories directly

If the caller passes O_DIRECTORY we just try to chdir() to smb_fname
directly, not to the parent directory.

The security check in check_reduced_name() will continue to work, but
this fixes the case of an open() for a previous version of a
subdirectory that contains snapshopt.

Eg:

[share]
    path = /shares/test
    vfs objects = shadow_copy2
    shadow:snapdir = .snapshots
    shadow:snapdirseverywhere = yes

Directory tree with fake snapshots:

$ tree -a /shares/test/
/shares/test/
├── dir
│   ├── file
│   └── .snapshots
│       └── @GMT-2017.07.04-04.30.12
│           └── file
├── dir2
│   └── file
├── file
├── .snapshots
│   └── @GMT-2001.01.01-00.00.00
│       ├── dir2
│       │   └── file
│       └── file
└── testfsctl.dat

./bin/smbclient -U slow%x //localhost/share -c 'ls @GMT-2017.07.04-04.30.12/dir/*'
NT_STATUS_OBJECT_NAME_NOT_FOUND listing \@GMT-2017.07.04-04.30.12\dir\*

Bug: https://bugzilla.samba.org/show_bug.cgi?id=12885

Signed-off-by: Ralph Boehme <slow@samba.org>
Reviewed-by: Jeremy Allison <jra@samba.org>
(cherry picked from commit b886a9443d49f6e27fa3863d87c9e24d12e62874)

Autobuild-User(v4-4-test): Karolin Seeger <kseeger@samba.org>
Autobuild-Date(v4-4-test): Mon Jul 24 04:25:45 CEST 2017 on sn-devel-144

1 files changed, 25 insertions, 5 deletions

diff --git a/source3/smbd/open.c b/source3/smbd/open.c
index f19af87103b..5efb6f56eb1 100644
--- a/source3/smbd/open.c
+++ b/source3/smbd/open.c
@@ -527,12 +527,32 @@ static int non_widelink_open(struct connection_struct *conn,
 	char *oldwd = NULL;
 	char *parent_dir = NULL;
 	const char *final_component = NULL;
+	bool is_directory = false;
+	bool ok;
 
-	if (!parent_dirname(talloc_tos(),
-			smb_fname->base_name,
-			&parent_dir,
-			&final_component)) {
-		goto out;
+#ifdef O_DIRECTORY
+	if (flags & O_DIRECTORY) {
+		is_directory = true;
+	}
+#endif
+
+	if (is_directory) {
+		parent_dir = talloc_strdup(talloc_tos(), smb_fname->base_name);
+		if (parent_dir == NULL) {
+			saved_errno = errno;
+			goto out;
+		}
+
+		final_component = ".";
+	} else {
+		ok = parent_dirname(talloc_tos(),
+				    smb_fname->base_name,
+				    &parent_dir,
+				    &final_component);
+		if (!ok) {
+			saved_errno = errno;
+			goto out;
+		}
 	}
 
 	oldwd = vfs_GetWd(talloc_tos(), conn);