Re: [PATCH][SMB3.1.1] add ability to send signing negotiate context

[Steve French <smfrench@gmail.com>]

It is a little tricky to figure out good wording here.

"enable_negotiate_signing" (eventually) could end up requesting all 3
... which means that the server could choose SHA256 over GMAC over
CMAC.  Maybe I should avoid all mention of GMAC.

My reason for noting "GMAC is experimental" is that if GMAC is
negotiated it is less tested than the other two (since fewer servers
currently support it compared to the other two which are broadly
supported and thus already tested with cifs.ko) - but the effect of
the patch is to let the server choose which algorithm it prefers ...
so perhaps I should avoid mentioning GMAC here.

On Thu, Jul 8, 2021 at 5:06 PM Pavel Shilovsky <piastryyy@gmail.com> wrote:
>
> @@ -104,6 +105,9 @@ MODULE_PARM_DESC(enable_gcm_256, "Enable
> requesting strongest (256 bit) GCM encr
>  module_param(require_gcm_256, bool, 0644);
>  MODULE_PARM_DESC(require_gcm_256, "Require strongest (256 bit) GCM
> encryption. Default: n/N/0");
>
> +module_param(enable_negotiate_signing, bool, 0644);
> +MODULE_PARM_DESC(enable_GMAC_signing, "Enable requesting faster
> (GMAC) packet signing. Default: n/N/0");
> +
>
> s/enable_GMAC_signing/enable_negotiate_signing/ ?
>
> Also the description here is misleading: this param enables sending
> the signing context not requesting GMAC which is not supported yet.
>
>
> +    if (enable_negotiate_signing) {
> +        pr_warn_once("requesting GMAC signing is experimental\n");
>
> Here as well - we are not requesting GMAC here, we are sending the
> signing context with CMAC. I don't think this should be marked as
> experimental.
>
> --
> Best regards,
> Pavel Shilovsky
>
> ср, 7 июл. 2021 г. в 21:52, ronnie sahlberg <ronniesahlberg@gmail.com>:
> >
> > lgtm
> >
> > On Thu, Jul 8, 2021 at 2:49 PM Steve French <smfrench@gmail.com> wrote:
> > >
> > > v4 of patch (includes minor change to set local variable "num_algs"
> > > once to number of algorithms and use that throughout
> > > build_signing_context to make code a little clearer)
> > >
> > >
> > > On Wed, Jul 7, 2021 at 11:27 PM Steve French <smfrench@gmail.com> wrote:
> > > >
> > > > v3 of patch.  Updated with additional feedback from Ronnie (to make it
> > > > more context len and datalength clearer)
> > > >
> > > >
> > > > On Wed, Jul 7, 2021 at 9:44 PM Steve French <smfrench@gmail.com> wrote:
> > > > >
> > > > > Support for faster packet signing (using GMAC instead of CMAC) can
> > > > > now be negotiated to some newer servers, including Windows.
> > > > > See MS-SMB2 section 2.2.3.17.
> > > > >
> > > > > This patch adds support for sending the new negotiate context
> > > > > with the first of three supported signing algorithms (AES-CMAC)
> > > > > and decoding the response.  A followon patch will add support
> > > > > for sending the other two (including AES-GMAC, which is fastest)
> > > > > and changing the signing algorithm used based on what was
> > > > > negotiated.
> > > > >
> > > > > To allow the client to request GMAC signing set module parameter
> > > > > "enable_negotiate_signing" to 1.
> > > > >
> > > > > Reviewed-by: Ronnie Sahlberg <lsahlber@redhat.com>
> > > > > Signed-off-by: Steve French <stfrench@microsoft.com>
> > > > > ---
> > > > >  fs/cifs/cifsfs.c   |  4 +++
> > > > >  fs/cifs/cifsglob.h |  3 ++
> > > > >  fs/cifs/smb2pdu.c  | 83 ++++++++++++++++++++++++++++++++++++++++------
> > > > >  fs/cifs/smb2pdu.h  |  5 ++-
> > > > >  4 files changed, 84 insertions(+), 11 deletions(-)
> > > > >
> > > > > diff --git a/fs/cifs/cifsfs.c b/fs/cifs/cifsfs.c
> > > > > index 9fb874dd8d24..476b07213fcd 100644
> > > > > --- a/fs/cifs/cifsfs.c
> > > > > +++ b/fs/cifs/cifsfs.c
> > > > > @@ -65,6 +65,7 @@ bool lookupCacheEnabled = true;
> > > > >  bool disable_legacy_dialects; /* false by default */
> > > > >  bool enable_gcm_256 = true;
> > > > >  bool require_gcm_256; /* false by default */
> > > > > +bool enable_negotiate_signing; /* false by default */
> > > > >  unsigned int global_secflags = CIFSSEC_DEF;
> > > > >  /* unsigned int ntlmv2_support = 0; */
> > > > >  unsigned int sign_CIFS_PDUs = 1;
> > > > > @@ -104,6 +105,9 @@ MODULE_PARM_DESC(enable_gcm_256, "Enable
> > > > > requesting strongest (256 bit) GCM encr
> > > > >  module_param(require_gcm_256, bool, 0644);
> > > > >  MODULE_PARM_DESC(require_gcm_256, "Require strongest (256 bit) GCM
> > > > > encryption. Default: n/N/0");
> > > > >
> > > > > +module_param(enable_negotiate_signing, bool, 0644);
> > > > > +MODULE_PARM_DESC(enable_GMAC_signing, "Enable requesting faster
> > > > > (GMAC) packet signing. Default: n/N/0");
> > > > > +
> > > > >  module_param(disable_legacy_dialects, bool, 0644);
> > > > >  MODULE_PARM_DESC(disable_legacy_dialects, "To improve security it may be "
> > > > >     "helpful to restrict the ability to "
> > > > > diff --git a/fs/cifs/cifsglob.h b/fs/cifs/cifsglob.h
> > > > > index 921680fb7931..3c2e117bb926 100644
> > > > > --- a/fs/cifs/cifsglob.h
> > > > > +++ b/fs/cifs/cifsglob.h
> > > > > @@ -667,9 +667,11 @@ struct TCP_Server_Info {
> > > > >   unsigned int max_write;
> > > > >   unsigned int min_offload;
> > > > >   __le16 compress_algorithm;
> > > > > + __u16 signing_algorithm;
> > > > >   __le16 cipher_type;
> > > > >   /* save initital negprot hash */
> > > > >   __u8 preauth_sha_hash[SMB2_PREAUTH_HASH_SIZE];
> > > > > + bool signing_negotiated; /* true if valid signing context rcvd from server */
> > > > >   bool posix_ext_supported;
> > > > >   struct delayed_work reconnect; /* reconnect workqueue job */
> > > > >   struct mutex reconnect_mutex; /* prevent simultaneous reconnects */
> > > > > @@ -1869,6 +1871,7 @@ extern unsigned int global_secflags; /* if on,
> > > > > session setup sent
> > > > >  extern unsigned int sign_CIFS_PDUs;  /* enable smb packet signing */
> > > > >  extern bool enable_gcm_256; /* allow optional negotiate of strongest
> > > > > signing (aes-gcm-256) */
> > > > >  extern bool require_gcm_256; /* require use of strongest signing
> > > > > (aes-gcm-256) */
> > > > > +extern bool enable_negotiate_signing; /* request use of faster (GMAC)
> > > > > signing if available */
> > > > >  extern bool linuxExtEnabled;/*enable Linux/Unix CIFS extensions*/
> > > > >  extern unsigned int CIFSMaxBufSize;  /* max size not including hdr */
> > > > >  extern unsigned int cifs_min_rcv;    /* min size of big ntwrk buf pool */
> > > > > diff --git a/fs/cifs/smb2pdu.c b/fs/cifs/smb2pdu.c
> > > > > index 962826dc3316..757f145e70e5 100644
> > > > > --- a/fs/cifs/smb2pdu.c
> > > > > +++ b/fs/cifs/smb2pdu.c
> > > > > @@ -433,6 +433,23 @@ build_compression_ctxt(struct
> > > > > smb2_compression_capabilities_context *pneg_ctxt)
> > > > >   pneg_ctxt->CompressionAlgorithms[2] = SMB3_COMPRESS_LZNT1;
> > > > >  }
> > > > >
> > > > > +static void
> > > > > +build_signing_ctxt(struct smb2_signing_capabilities *pneg_ctxt)
> > > > > +{
> > > > > + pneg_ctxt->ContextType = SMB2_SIGNING_CAPABILITIES;
> > > > > + /*
> > > > > + * Data length must be increased here if more than 3 signing algorithms
> > > > > + * sent but currently only 3 are defined. And context Data length must
> > > > > + * be rounded to multiple of 8 for some servers.
> > > > > + */
> > > > > + pneg_ctxt->DataLength =
> > > > > + cpu_to_le16(DIV_ROUND_UP(sizeof(struct smb2_signing_capabilities) -
> > > > > + sizeof(struct smb2_neg_context), 8) * 8);
> > > > > + pneg_ctxt->SigningAlgorithmCount = cpu_to_le16(1);
> > > > > + pneg_ctxt->SigningAlgorithms[0] = cpu_to_le16(SIGNING_ALG_AES_CMAC);
> > > > > + /* TBD add SIGNING_ALG_AES_GMAC and/or SIGNING_ALG_HMAC_SHA256 */
> > > > > +}
> > > > > +
> > > > >  static void
> > > > >  build_encrypt_ctxt(struct smb2_encryption_neg_context *pneg_ctxt)
> > > > >  {
> > > > > @@ -498,7 +515,7 @@ assemble_neg_contexts(struct smb2_negotiate_req *req,
> > > > >         struct TCP_Server_Info *server, unsigned int *total_len)
> > > > >  {
> > > > >   char *pneg_ctxt;
> > > > > - unsigned int ctxt_len;
> > > > > + unsigned int ctxt_len, neg_context_count;
> > > > >
> > > > >   if (*total_len > 200) {
> > > > >   /* In case length corrupted don't want to overrun smb buffer */
> > > > > @@ -525,6 +542,17 @@ assemble_neg_contexts(struct smb2_negotiate_req *req,
> > > > >   *total_len += ctxt_len;
> > > > >   pneg_ctxt += ctxt_len;
> > > > >
> > > > > + ctxt_len = build_netname_ctxt((struct smb2_netname_neg_context *)pneg_ctxt,
> > > > > + server->hostname);
> > > > > + *total_len += ctxt_len;
> > > > > + pneg_ctxt += ctxt_len;
> > > > > +
> > > > > + build_posix_ctxt((struct smb2_posix_neg_context *)pneg_ctxt);
> > > > > + *total_len += sizeof(struct smb2_posix_neg_context);
> > > > > + pneg_ctxt += sizeof(struct smb2_posix_neg_context);
> > > > > +
> > > > > + neg_context_count = 4;
> > > > > +
> > > > >   if (server->compress_algorithm) {
> > > > >   build_compression_ctxt((struct smb2_compression_capabilities_context *)
> > > > >   pneg_ctxt);
> > > > > @@ -533,17 +561,24 @@ assemble_neg_contexts(struct smb2_negotiate_req *req,
> > > > >   8) * 8;
> > > > >   *total_len += ctxt_len;
> > > > >   pneg_ctxt += ctxt_len;
> > > > > - req->NegotiateContextCount = cpu_to_le16(5);
> > > > > - } else
> > > > > - req->NegotiateContextCount = cpu_to_le16(4);
> > > > > + neg_context_count++;
> > > > > + }
> > > > >
> > > > > - ctxt_len = build_netname_ctxt((struct smb2_netname_neg_context *)pneg_ctxt,
> > > > > - server->hostname);
> > > > > - *total_len += ctxt_len;
> > > > > - pneg_ctxt += ctxt_len;
> > > > > + if (enable_negotiate_signing) {
> > > > > + pr_warn_once("requesting GMAC signing is experimental\n");
> > > > > + build_signing_ctxt((struct smb2_signing_capabilities *)
> > > > > + pneg_ctxt);
> > > > > + ctxt_len = DIV_ROUND_UP(
> > > > > + sizeof(struct smb2_signing_capabilities),
> > > > > + 8) * 8;
> > > > > + *total_len += ctxt_len;
> > > > > + pneg_ctxt += ctxt_len;
> > > > > + neg_context_count++;
> > > > > + }
> > > > > +
> > > > > + /* check for and add transport_capabilities and signing capabilities */
> > > > > + req->NegotiateContextCount = cpu_to_le16(neg_context_count);
> > > > >
> > > > > - build_posix_ctxt((struct smb2_posix_neg_context *)pneg_ctxt);
> > > > > - *total_len += sizeof(struct smb2_posix_neg_context);
> > > > >  }
> > > > >
> > > > >  static void decode_preauth_context(struct smb2_preauth_neg_context *ctxt)
> > > > > @@ -632,6 +667,31 @@ static int decode_encrypt_ctx(struct
> > > > > TCP_Server_Info *server,
> > > > >   return 0;
> > > > >  }
> > > > >
> > > > > +static void decode_signing_ctx(struct TCP_Server_Info *server,
> > > > > +        struct smb2_signing_capabilities *pctxt)
> > > > > +{
> > > > > + unsigned int len = le16_to_cpu(pctxt->DataLength);
> > > > > +
> > > > > + if ((len < 4) || (len > 16)) {
> > > > > + pr_warn_once("server sent bad signing negcontext\n");
> > > > > + return;
> > > > > + }
> > > > > + if (le16_to_cpu(pctxt->SigningAlgorithmCount) != 1) {
> > > > > + pr_warn_once("Invalid signing algorithm count\n");
> > > > > + return;
> > > > > + }
> > > > > + if (le16_to_cpu(pctxt->SigningAlgorithms[0]) > 2) {
> > > > > + pr_warn_once("unknown signing algorithm\n");
> > > > > + return;
> > > > > + }
> > > > > +
> > > > > + server->signing_negotiated = true;
> > > > > + server->signing_algorithm = le16_to_cpu(pctxt->SigningAlgorithms[0]);
> > > > > + cifs_dbg(FYI, "signing algorithm %d chosen\n",
> > > > > +      server->signing_algorithm);
> > > > > +}
> > > > > +
> > > > > +
> > > > >  static int smb311_decode_neg_context(struct smb2_negotiate_rsp *rsp,
> > > > >        struct TCP_Server_Info *server,
> > > > >        unsigned int len_of_smb)
> > > > > @@ -675,6 +735,9 @@ static int smb311_decode_neg_context(struct
> > > > > smb2_negotiate_rsp *rsp,
> > > > >   (struct smb2_compression_capabilities_context *)pctx);
> > > > >   else if (pctx->ContextType == SMB2_POSIX_EXTENSIONS_AVAILABLE)
> > > > >   server->posix_ext_supported = true;
> > > > > + else if (pctx->ContextType == SMB2_SIGNING_CAPABILITIES)
> > > > > + decode_signing_ctx(server,
> > > > > + (struct smb2_signing_capabilities *)pctx);
> > > > >   else
> > > > >   cifs_server_dbg(VFS, "unknown negcontext of type %d ignored\n",
> > > > >   le16_to_cpu(pctx->ContextType));
> > > > > diff --git a/fs/cifs/smb2pdu.h b/fs/cifs/smb2pdu.h
> > > > > index ba75e65924ac..4b27cb9105fd 100644
> > > > > --- a/fs/cifs/smb2pdu.h
> > > > > +++ b/fs/cifs/smb2pdu.h
> > > > > @@ -329,7 +329,7 @@ struct smb2_neg_context {
> > > > >   __le16 ContextType;
> > > > >   __le16 DataLength;
> > > > >   __le32 Reserved;
> > > > > - /* Followed by array of data */
> > > > > + /* Followed by array of data. NOTE: some servers require padding to
> > > > > 8 byte boundary */
> > > > >  } __packed;
> > > > >
> > > > >  #define SMB311_LINUX_CLIENT_SALT_SIZE 32
> > > > > @@ -394,6 +394,7 @@ struct smb2_compression_capabilities_context {
> > > > >   __u16 Padding;
> > > > >   __u32 Flags;
> > > > >   __le16 CompressionAlgorithms[3];
> > > > > + /* Check if pad needed */
> > > > >  } __packed;
> > > > >
> > > > >  /*
> > > > > @@ -420,6 +421,7 @@ struct smb2_transport_capabilities_context {
> > > > >   __le16  DataLength;
> > > > >   __u32 Reserved;
> > > > >   __le32 Flags;
> > > > > + __u32 Pad;
> > > > >  } __packed;
> > > > >
> > > > >  /*
> > > > > @@ -458,6 +460,7 @@ struct smb2_signing_capabilities {
> > > > >   __u32 Reserved;
> > > > >   __le16 SigningAlgorithmCount;
> > > > >   __le16 SigningAlgorithms[];
> > > > > + /*  Followed by padding to 8 byte boundary (required by some servers) */
> > > > >  } __packed;
> > > > >
> > > > >  #define POSIX_CTXT_DATA_LEN 16
> > > > >
> > > > > --
> > > > > Thanks,
> > > > >
> > > > > Steve
> > > >
> > > >
> > > >
> > > > --
> > > > Thanks,
> > > >
> > > > Steve
> > >
> > >
> > >
> > > --
> > > Thanks,
> > >
> > > Steve



-- 
Thanks,

Steve