Re: [PATCH] cifs: implementation id context as negotiate context

Shyam Prasad N
2026-03-04T12:34:21Z

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On Wed, Mar 4, 2026 at 5:59 PM <nspmangalore@gmail.com> wrote:
>
> From: Shyam Prasad N <sprasad@microsoft.com>
>
> MS-SMB2 does not allow any fields for the client to communicate
> the client version details to the server. This change is a
> proof-of-concept to add client details in a new negotiate context.
>
> Signed-off-by: Shyam Prasad N <sprasad@microsoft.com>
> ---
> fs/smb/client/smb2pdu.c | 78 +++++++++++++++++++++++++++++++++++++++++
> fs/smb/common/smb2pdu.h | 32 +++++++++++++++++
> 2 files changed, 110 insertions(+)
>
> diff --git a/fs/smb/client/smb2pdu.c b/fs/smb/client/smb2pdu.c
> index ef655acf673df..9c89f6b4a6709 100644
> --- a/fs/smb/client/smb2pdu.c
> +++ b/fs/smb/client/smb2pdu.c
> @@ -24,6 +24,7 @@
> #include <linux/pagemap.h>
> #include <linux/xattr.h>
> #include <linux/netfs.h>
> +#include <linux/utsname.h>
> #include <trace/events/netfs.h>
> #include "cifsglob.h"
> #include "cifsproto.h"
> @@ -45,6 +46,7 @@
> #include "cached_dir.h"
> #include "compress.h"
> #include "fs_context.h"
> +#include "cifsfs.h"
>
> /*
> * The following table defines the expected "StructureSize" of SMB2 requests
> @@ -724,6 +726,75 @@ build_posix_ctxt(struct smb2_posix_neg_context *pneg_ctxt)
> pneg_ctxt->Name[15] = 0x7C;
> }
>
> +static unsigned int
> +build_implementation_id_ctxt(struct smb2_implementation_id_context *pneg_ctxt)
> +{
> + struct nls_table *cp = load_nls_default();
> + struct new_utsname *uts = utsname();
> + const char *impl_domain = "kernel.org";
> + const char *impl_name = "fs/smb/client";
> + const char *os_name = "Linux";
> + unsigned int data_len = 0;
> + __u8 *data_ptr;
> + int len;
> +
> + pneg_ctxt->ContextType = SMB2_IMPLEMENTATION_ID_CONTEXT_ID;
> + data_ptr = pneg_ctxt->Data;
> +
> + /* ImplDomain */
> + len = cifs_strtoUTF16((__le16 *)data_ptr, impl_domain,
> + SMB2_IMPL_ID_MAX_DOMAIN_LEN, cp);
> + pneg_ctxt->ImplDomainLength = cpu_to_le16(len * 2);
> + data_ptr += len * 2;
> + data_len += len * 2;
> +
> + /* ImplName */
> + len = cifs_strtoUTF16((__le16 *)data_ptr, impl_name,
> + SMB2_IMPL_ID_MAX_NAME_LEN, cp);
> + pneg_ctxt->ImplNameLength = cpu_to_le16(len * 2);
> + data_ptr += len * 2;
> + data_len += len * 2;
> +
> + /* ImplVersion - CIFS_VERSION from cifsfs.h */
> + len = cifs_strtoUTF16((__le16 *)data_ptr, CIFS_VERSION,
> + SMB2_IMPL_ID_MAX_VERSION_LEN, cp);
> + pneg_ctxt->ImplVersionLength = cpu_to_le16(len * 2);
> + data_ptr += len * 2;
> + data_len += len * 2;
> +
> + /* HostName - from utsname()->nodename */
> + len = cifs_strtoUTF16((__le16 *)data_ptr, uts->nodename,
> + SMB2_IMPL_ID_MAX_HOSTNAME_LEN, cp);
> + pneg_ctxt->HostNameLength = cpu_to_le16(len * 2);
> + data_ptr += len * 2;
> + data_len += len * 2;
> +
> + /* OSName */
> + len = cifs_strtoUTF16((__le16 *)data_ptr, os_name,
> + SMB2_IMPL_ID_MAX_OS_NAME_LEN, cp);
> + pneg_ctxt->OSNameLength = cpu_to_le16(len * 2);
> + data_ptr += len * 2;
> + data_len += len * 2;
> +
> + /* OSVersion - from utsname()->release */
> + len = cifs_strtoUTF16((__le16 *)data_ptr, uts->release,
> + SMB2_IMPL_ID_MAX_OS_VERSION_LEN, cp);
> + pneg_ctxt->OSVersionLength = cpu_to_le16(len * 2);
> + data_ptr += len * 2;
> + data_len += len * 2;
> +
> + /* Arch - from utsname()->machine */
> + len = cifs_strtoUTF16((__le16 *)data_ptr, uts->machine,
> + SMB2_IMPL_ID_MAX_ARCH_LEN, cp);
> + pneg_ctxt->ArchLength = cpu_to_le16(len * 2);
> + data_len += len * 2;
> +
> + pneg_ctxt->Reserved2 = 0;
> + pneg_ctxt->DataLength = cpu_to_le16(data_len + 14); /* 14 = 7 length fields * 2 bytes */
> + /* Context size is DataLength + minimal smb2_neg_context, aligned to 8 */
> + return ALIGN(le16_to_cpu(pneg_ctxt->DataLength) + sizeof(struct smb2_neg_context), 8);
> +}
> +
> static void
> assemble_neg_contexts(struct smb2_negotiate_req *req,
> struct TCP_Server_Info *server, unsigned int *total_len)
> @@ -797,6 +868,13 @@ assemble_neg_contexts(struct smb2_negotiate_req *req,
> neg_context_count++;
> }
>
> + /* Add implementation ID context */
> + ctxt_len = build_implementation_id_ctxt((struct smb2_implementation_id_context *)
> + pneg_ctxt);
> + *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);
>
> diff --git a/fs/smb/common/smb2pdu.h b/fs/smb/common/smb2pdu.h
> index e482c86ceb00d..1ad7b57ce2952 100644
> --- a/fs/smb/common/smb2pdu.h
> +++ b/fs/smb/common/smb2pdu.h
> @@ -457,6 +457,7 @@ struct smb2_tree_disconnect_rsp {
> #define SMB2_TRANSPORT_CAPABILITIES cpu_to_le16(6)
> #define SMB2_RDMA_TRANSFORM_CAPABILITIES cpu_to_le16(7)
> #define SMB2_SIGNING_CAPABILITIES cpu_to_le16(8)
> +#define SMB2_IMPLEMENTATION_ID_CONTEXT_ID cpu_to_le16(0xF100)
> #define SMB2_POSIX_EXTENSIONS_AVAILABLE cpu_to_le16(0x100)
>
> struct smb2_neg_context {
> @@ -596,6 +597,37 @@ struct smb2_signing_capabilities {
> /* Followed by padding to 8 byte boundary (required by some servers) */
> } __packed;
>
> +/*
> + * For implementation ID context see MS-SMB2 2.2.3.1.8
> + * Maximum string lengths per specification
> + */
> +#define SMB2_IMPL_ID_MAX_DOMAIN_LEN 128
> +#define SMB2_IMPL_ID_MAX_NAME_LEN 260
> +#define SMB2_IMPL_ID_MAX_VERSION_LEN 260
> +#define SMB2_IMPL_ID_MAX_HOSTNAME_LEN 64
> +#define SMB2_IMPL_ID_MAX_OS_NAME_LEN 64
> +#define SMB2_IMPL_ID_MAX_OS_VERSION_LEN 64
> +#define SMB2_IMPL_ID_MAX_ARCH_LEN 64
> +
> +struct smb2_implementation_id_context {
> + __le16 ContextType; /* 9 */
> + __le16 DataLength;
> + __le32 Reserved;
> + __le16 ImplDomainLength;
> + __le16 ImplNameLength;
> + __le16 ImplVersionLength;
> + __le16 HostNameLength;
> + __le16 OSNameLength;
> + __le16 OSVersionLength;
> + __le16 ArchLength;
> + __le16 Reserved2;
> + /* Followed by variable length UTF-16 strings:
> + * ImplDomain, ImplName, ImplVersion, HostName,
> + * OSName, OSVersion, Arch
> + */
> + __u8 Data[];
> +} __packed;
> +
> #define POSIX_CTXT_DATA_LEN 16
> struct smb2_posix_neg_context {
> __le16 ContextType; /* 0x100 */
> --
> 2.43.0
>

A proof-of-concept based on this draft from Bharath.
Looking for comments on how to improve.

--
Regards,
Shyam

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