[PATCH] Small enhancement to vfs_fruit

[Ralph Böhme]

Hi!

Attached is a small improvement for vfs_fruit that helps users that appyl 
additional patches on-top of Samba. The commit messages has the nasty 
details. :)

Please review & push if happy. Thanks!

-slow

-- 
Ralph Boehme, Samba Team                https://samba.org/
Samba Developer, SerNet GmbH   https://sernet.de/en/samba/
GPG-Fingerprint   FAE2C6088A24252051C559E4AA1E9B7126399E46
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From 37b714865657c791416f992a6c0e6d9926601630 Mon Sep 17 00:00:00 2001
From: Ralph Boehme <slow at samba.org>
Date: Fri, 30 Nov 2018 10:27:19 +0100
Subject: [PATCH] vfs_fruit: avoid dereferencing fsp->base_fsp in
 fruit_fstat_meta_stream()

This helps avoiding a NULL dereference on systems where additional
patches modify the following condition in open_file()

  if ((open_access_mask & (FILE_READ_DATA|FILE_WRITE_DATA|FILE_APPEND_DATA|FILE_EXECUTE)) ||
      (!file_existed && (local_flags & O_CREAT)) ||
      ((local_flags & O_TRUNC) == O_TRUNC) ) {

to

  if ((open_access_mask & (FILE_READ_DATA|FILE_WRITE_DATA|FILE_APPEND_DATA|FILE_EXECUTE|DELETE_ACCESS)) ||
      (!file_existed && (local_flags & O_CREAT)) ||
      ((local_flags & O_TRUNC) == O_TRUNC) ) {

Ie addtionally check open_access_mask against DELETE_ACCESS. As a result
opens with DELETE_ACCESS go through the code that does an fd_open() plus
a subsequent fstat().

That will trigger a crash in fruit_fstat_meta_stream() when a client
wants to delete a file for deletion. When we open base file for delete,
we call open_streams_for_delete() which internally calls create-file
with NTCREATEX_OPTIONS_PRIVATE_STREAM_DELETE which prevents opening of
the base_fsp. Voila, combined with the change described above you get a
NULL deref.

Signed-off-by: Ralph Boehme <slow at samba.org>
---
 source3/modules/vfs_fruit.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/source3/modules/vfs_fruit.c b/source3/modules/vfs_fruit.c
index 50b6fac8b95..19101efba74 100644
--- a/source3/modules/vfs_fruit.c
+++ b/source3/modules/vfs_fruit.c
@@ -5204,6 +5204,7 @@ static int fruit_fstat_meta_stream(vfs_handle_struct *handle,
 				   SMB_STRUCT_STAT *sbuf)
 {
 	struct fio *fio = (struct fio *)VFS_FETCH_FSP_EXTENSION(handle, fsp);
+	struct smb_filename smb_fname;
 	ino_t ino;
 	int ret;
 
@@ -5223,11 +5224,15 @@ static int fruit_fstat_meta_stream(vfs_handle_struct *handle,
 		return 0;
 	}
 
-	ret = fruit_stat_base(handle, fsp->base_fsp->fsp_name, false);
+	smb_fname = (struct smb_filename) {
+		.base_name = fsp->fsp_name->base_name,
+	};
+
+	ret = fruit_stat_base(handle, &smb_fname, false);
 	if (ret != 0) {
 		return -1;
 	}
-	*sbuf = fsp->base_fsp->fsp_name->st;
+	*sbuf = smb_fname.st;
 
 	ino = fruit_inode(sbuf, fsp->fsp_name->stream_name);
 
-- 
2.17.2