[Samba] FreeBSD samba server returns nt_status_acces_denied when DosStream xattr larger than 64KB

[Andrew Walker]

I wrote a powershell script on a windows computer to write an ADS on a file
on a FreeBSD server with streams_xattr enabled. If it's smaller than 64KB,
it succeeds. If it's larger than 64KB, I get an "access denied message" and
powershell crashes. FreeBSD actually allows creation of large extended
attributes (at least on ZFS volumes). I've personally added ones of up to
3MB in size, but have never actually tested the limits.

For the fun of it I decided to run the following command from the CLI in
FreeBSD "cat <large file> | setextattr -i user
'DosStream.User.SecretStream:$DATA' test.txt" This had the effect of
creating something that samba should recognize as an ADS that is
arbitrarily large.

If I run the following powershell command from a Windows client "Get-Item
-Path .\test.txt -stream *", I do not see the ADS listed unless it is
smaller than 64KB. When it is larger than it, and I have logging ratcheted
up I get logs like below. Out of curiousity, does Samba not support large
ADS? Do you have any pointers on how to maybe coax Samba into letting me
abuse xattrs better?

[2017/08/02 10:55:51.475689, 10, pid=43437, effective(21112, 20513),
real(0, 0), class=vfs]
../source3/modules/vfs_streams_xattr.c:753(walk_xattr_streams)
  Could not get ea user.DosStream.User.SecretStream:$DATA for file
test2.txt: NT_STATUS_ACCESS_DENIED
[2017/08/02 10:55:51.475753, 10, pid=43437, effective(21112, 20513),
real(0, 0)] ../source3/smbd/trans2.c:4685(marshall_stream_info)
  refusing to overflow reply at stream 0
[2017/08/02 10:55:51.475771, 10, pid=43437, effective(21112, 20513),
real(0, 0)] ../source3/smbd/trans2.c:5358(smbd_do_qfilepathinfo)
  marshall_stream_info failed: STATUS_BUFFER_OVERFLOW
[2017/08/02 10:55:51.475789,  3, pid=43437, effective(21112, 20513),
real(0, 0)] ../source3/smbd/smb2_server.c:3097(smbd_smb2_request_error_ex)
  smbd_smb2_request_error_ex: smbd_smb2_request_error_ex: idx[5]
status[STATUS_BUFFER_OVERFLOW] || at ../source3/smbd/smb2_getinfo.c:154
[2017/08/02 10:55:51.475807, 10, pid=43437, effective(21112, 20513),
real(0, 0)] ../source3/smbd/smb2_server.c:2988(smbd_smb2_request_done_ex)
  smbd_smb2_request_done_ex: idx[5] status[STATUS_BUFFER_OVERFLOW] body[8]
dyn[yes:1] at ../source3/smbd/smb2_server.c:3145