Messages in this thread | | | Date | Wed, 16 Nov 2022 09:36:04 +0100 | Subject | Re: [PATCH] cifs: Fix problem with encrypted RDMA data read | From | Stefan Metzmacher <> |
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Am 16.11.22 um 06:19 schrieb Namjae Jeon: > 2022-11-16 9:57 GMT+09:00, Stefan Metzmacher <metze@samba.org>: >> Hi David, >> >> see below... >> >>> When the cifs client is talking to the ksmbd server by RDMA and the ksmbd >>> server has "smb3 encryption = yes" in its config file, the normal PDU >>> stream is encrypted, but the directly-delivered data isn't in the stream >>> (and isn't encrypted), but is rather delivered by DDP/RDMA packets (at >>> least with IWarp). >>> >>> Currently, the direct delivery fails with: >>> >>> buf can not contain only a part of read data >>> WARNING: CPU: 0 PID: 4619 at fs/cifs/smb2ops.c:4731 >>> handle_read_data+0x393/0x405 >>> ... >>> RIP: 0010:handle_read_data+0x393/0x405 >>> ... >>> smb3_handle_read_data+0x30/0x37 >>> receive_encrypted_standard+0x141/0x224 >>> cifs_demultiplex_thread+0x21a/0x63b >>> kthread+0xe7/0xef >>> ret_from_fork+0x22/0x30 >>> >>> The problem apparently stemming from the fact that it's trying to manage >>> the decryption, but the data isn't in the smallbuf, the bigbuf or the >>> page >>> array). >>> >>> This can be fixed simply by inserting an extra case into >>> handle_read_data() >>> that checks to see if use_rdma_mr is true, and if it is, just setting >>> rdata->got_bytes to the length of data delivered and allowing normal >>> continuation. >>> >>> This can be seen in an IWarp packet trace. With the upstream code, it >>> does >>> a DDP/RDMA packet, which produces the warning above and then retries, >>> retrieving the data inline, spread across several SMBDirect messages that >>> get glued together into a single PDU. With the patch applied, only the >>> DDP/RDMA packet is seen. >>> >>> Note that this doesn't happen if the server isn't told to encrypt stuff >>> and >>> it does also happen with softRoCE. >>> >>> Signed-off-by: David Howells <dhowells@redhat.com> >>> cc: Steve French <smfrench@gmail.com> >>> cc: Tom Talpey <tom@talpey.com> >>> cc: Long Li <longli@microsoft.com> >>> cc: Namjae Jeon <linkinjeon@kernel.org> >>> cc: Stefan Metzmacher <metze@samba.org> >>> cc: linux-cifs@vger.kernel.org >>> --- >>> >>> fs/cifs/smb2ops.c | 3 +++ >>> 1 file changed, 3 insertions(+) >>> >>> diff --git a/fs/cifs/smb2ops.c b/fs/cifs/smb2ops.c >>> index 880cd494afea..8d459f60f27b 100644 >>> --- a/fs/cifs/smb2ops.c >>> +++ b/fs/cifs/smb2ops.c >>> @@ -4726,6 +4726,9 @@ handle_read_data(struct TCP_Server_Info *server, >>> struct mid_q_entry *mid, >>> iov.iov_base = buf + data_offset; >>> iov.iov_len = data_len; >>> iov_iter_kvec(&iter, WRITE, &iov, 1, data_len); >>> + } else if (use_rdma_mr) { >>> + /* The data was delivered directly by RDMA. */ >>> + rdata->got_bytes = data_len; >>> } else { >>> /* read response payload cannot be in both buf and pages */ >>> WARN_ONCE(1, "buf can not contain only a part of read data"); >> >> I'm not sure I understand why this would fix anything when encryption is >> enabled. >> >> Is the payload still be offloaded as plaintext? Otherwise we wouldn't have >> use_rdma_mr... >> So this rather looks like a fix for the non encrypted case. > ksmbd doesn't encrypt RDMA payload on read/write operation, Currently > only smb2 response is encrypted for this. And as you pointed out, We > need to implement SMB2 RDMA Transform to encrypt it.
I haven't tested against a windows server yet, but my hope would be that and encrypted request with SMB2_CHANNEL_RDMA_V1* receive NT_STATUS_ACCESS_DENIED or something similar...
Is someone able to check that against Windows?
But the core of it is a client security problem, shown in David's capture in frame 100.
metze
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