* [PATCH 1/2] ksmbd: sign with the negotiated SMB 3.1.1 signing algorithm
2026-11-03 11:14 [PATCH 0/2] ksmbd: AES-GMAC signing support Michail Andreas Michalopoulos
@ 2026-11-03 11:14 ` Michail Andreas Michalopoulos
2026-11-03 11:14 ` [PATCH 2/2] ksmbd: add AES-GMAC signing support Michail Andreas Michalopoulos
1 sibling, 0 replies; 4+ messages in thread
From: Michail Andreas Michalopoulos @ 2026-11-03 11:14 UTC (permalink / raw)
To: Namjae Jeon
Cc: Michail Andreas Michalopoulos, Sergey Senozhatsky, Tom Talpey,
ChenXiaoSong, Enzo Matsumiya, linux-cifs, linux-doc,
linux-kernel
decode_sign_cap_ctxt() stores the algorithm picked from the client's
SMB2_SIGNING_CAPABILITIES context in conn->signing_algorithm, but it
runs before init_smb3_11_server(), which then overwrites it with
AES-CMAC. As a result the negotiate response always selects AES-CMAC,
even for a client that only offered HMAC-SHA256, and every SMB 3.1.1
connection is signed with AES-CMAC.
Keep the negotiated algorithm and sign with HMAC-SHA256 when that is
what was negotiated.
Since connections of the same session can now use different
algorithms, each signing key also has to be used with the algorithm it
was created for. The session signing key belongs to the connection
that set up the session, and MS-SMB2 3.3.5.5 requires a binding
request on a new channel to be verified with it. Store that
connection's algorithm in the session and use it together with the
session key, while channel keys keep using their own connection's
algorithm.
An AI assistant was used to draft the patch and as an independent
reviewer. Testing is described in the cover letter.
Fixes: 378087cd17ee ("ksmbd: add support for negotiating signing algorithm")
Signed-off-by: Michail Andreas Michalopoulos <mike.michalo@gmail.com>
---
fs/smb/server/auth.c | 14 ++++++++++++--
fs/smb/server/auth.h | 4 ++--
fs/smb/server/mgmt/user_session.c | 1 +
fs/smb/server/mgmt/user_session.h | 2 ++
fs/smb/server/smb2ops.c | 4 +++-
fs/smb/server/smb2pdu.c | 18 ++++++++++++++++--
6 files changed, 36 insertions(+), 7 deletions(-)
diff --git a/fs/smb/server/auth.c b/fs/smb/server/auth.c
index 0c51ca0cb14..78e35f21746 100644
--- a/fs/smb/server/auth.c
+++ b/fs/smb/server/auth.c
@@ -504,19 +504,29 @@ void ksmbd_sign_smb2_pdu(struct ksmbd_conn *conn, char *key, struct kvec *iov,
/**
* ksmbd_sign_smb3_pdu() - function to generate packet signing
* @conn: connection
+ * @signing_algorithm: signing algorithm the key was generated for
* @key: signing key
* @iov: buffer iov array
* @n_vec: number of iovecs
* @sig: signature value generated for client request packet
*
*/
-void ksmbd_sign_smb3_pdu(struct ksmbd_conn *conn, char *key, struct kvec *iov,
- int n_vec, char *sig)
+void ksmbd_sign_smb3_pdu(struct ksmbd_conn *conn, __le16 signing_algorithm,
+ char *key, struct kvec *iov, int n_vec, char *sig)
{
struct aes_cmac_key cmac_key __cleanup(aes_cmac_zeroize_key);
struct aes_cmac_ctx cmac_ctx;
int i;
+ if (signing_algorithm == SIGNING_ALG_HMAC_SHA256_LE) {
+ u8 mac[SHA256_DIGEST_SIZE];
+
+ ksmbd_sign_smb2_pdu(conn, key, iov, n_vec, mac);
+ memcpy(sig, mac, SMB2_SIGNATURE_SIZE);
+ memzero_explicit(mac, sizeof(mac));
+ return;
+ }
+
/* This cannot fail, since we always pass a valid key length. */
static_assert(SMB2_CMACAES_SIZE == AES_KEYSIZE_128);
aes_cmac_preparekey(&cmac_key, key, SMB2_CMACAES_SIZE);
diff --git a/fs/smb/server/auth.h b/fs/smb/server/auth.h
index 7ce9c42d58f..5a10482678e 100644
--- a/fs/smb/server/auth.h
+++ b/fs/smb/server/auth.h
@@ -59,8 +59,8 @@ int ksmbd_krb5_authenticate(struct ksmbd_session *sess, char *in_blob,
char *sess_key);
void ksmbd_sign_smb2_pdu(struct ksmbd_conn *conn, char *key, struct kvec *iov,
int n_vec, char *sig);
-void ksmbd_sign_smb3_pdu(struct ksmbd_conn *conn, char *key, struct kvec *iov,
- int n_vec, char *sig);
+void ksmbd_sign_smb3_pdu(struct ksmbd_conn *conn, __le16 signing_algorithm,
+ char *key, struct kvec *iov, int n_vec, char *sig);
int ksmbd_gen_smb30_signingkey(struct ksmbd_session *sess,
struct ksmbd_conn *conn);
int ksmbd_gen_smb311_signingkey(struct ksmbd_session *sess,
diff --git a/fs/smb/server/mgmt/user_session.c b/fs/smb/server/mgmt/user_session.c
index 3f75049be87..42419bc0cea 100644
--- a/fs/smb/server/mgmt/user_session.c
+++ b/fs/smb/server/mgmt/user_session.c
@@ -553,6 +553,7 @@ int ksmbd_session_register(struct ksmbd_conn *conn,
int ret;
sess->dialect = conn->dialect;
+ sess->signing_algorithm = conn->signing_algorithm;
memcpy(sess->ClientGUID, conn->ClientGUID, SMB2_CLIENT_GUID_SIZE);
ret = xa_err(xa_store(&conn->sessions, sess->id, sess,
KSMBD_DEFAULT_GFP));
diff --git a/fs/smb/server/mgmt/user_session.h b/fs/smb/server/mgmt/user_session.h
index 5f0f6276e31..931ca102b83 100644
--- a/fs/smb/server/mgmt/user_session.h
+++ b/fs/smb/server/mgmt/user_session.h
@@ -48,6 +48,8 @@ struct ksmbd_session {
u64 id;
__u16 dialect;
+ /* Signing algorithm of the connection that created the session */
+ __le16 signing_algorithm;
char ClientGUID[SMB2_CLIENT_GUID_SIZE];
struct ksmbd_user *user;
diff --git a/fs/smb/server/smb2ops.c b/fs/smb/server/smb2ops.c
index 747276b171b..c5b3cf34494 100644
--- a/fs/smb/server/smb2ops.c
+++ b/fs/smb/server/smb2ops.c
@@ -320,7 +320,9 @@ int init_smb3_11_server(struct ksmbd_conn *conn)
conn->ops = &smb3_11_server_ops;
conn->cmds = smb2_0_server_cmds;
conn->max_cmds = ARRAY_SIZE(smb2_0_server_cmds);
- conn->signing_algorithm = SIGNING_ALG_AES_CMAC_LE;
+ /* Keep the algorithm chosen from the client's signing capabilities */
+ if (!conn->signing_negotiated)
+ conn->signing_algorithm = SIGNING_ALG_AES_CMAC_LE;
if (server_conf.flags & KSMBD_GLOBAL_FLAG_SMB2_LEASES)
conn->vals->req_capabilities |= SMB2_GLOBAL_CAP_LEASING |
diff --git a/fs/smb/server/smb2pdu.c b/fs/smb/server/smb2pdu.c
index 2e955d272f4..11994e6b92e 100644
--- a/fs/smb/server/smb2pdu.c
+++ b/fs/smb/server/smb2pdu.c
@@ -12919,6 +12919,7 @@ int smb3_check_sign_req(struct ksmbd_work *work)
{
struct ksmbd_conn *conn = work->conn;
char *signing_key;
+ __le16 signing_algorithm;
struct smb2_hdr *hdr;
struct channel *chann;
char signature_req[SMB2_SIGNATURE_SIZE];
@@ -12938,8 +12939,14 @@ int smb3_check_sign_req(struct ksmbd_work *work)
len = get_rfc1002_len(work->request_buf) -
work->next_smb2_rcv_hdr_off;
+ /*
+ * A key must be used with the algorithm it was generated for: the
+ * session key with the one of the connection that created the
+ * session, which can differ from this connection's when binding.
+ */
if (le16_to_cpu(hdr->Command) == SMB2_SESSION_SETUP_HE) {
signing_key = work->sess->smb3signingkey;
+ signing_algorithm = work->sess->signing_algorithm;
} else {
chann = lookup_chann_list(work->sess, conn);
if (!chann) {
@@ -12947,8 +12954,10 @@ int smb3_check_sign_req(struct ksmbd_work *work)
!(hdr->Flags & SMB2_FLAGS_SIGNED))
return 0;
signing_key = work->sess->smb3signingkey;
+ signing_algorithm = work->sess->signing_algorithm;
} else {
signing_key = chann->smb3signingkey;
+ signing_algorithm = conn->signing_algorithm;
}
}
@@ -12962,7 +12971,8 @@ int smb3_check_sign_req(struct ksmbd_work *work)
iov[0].iov_base = (char *)&hdr->ProtocolId;
iov[0].iov_len = len;
- ksmbd_sign_smb3_pdu(conn, signing_key, iov, 1, signature);
+ ksmbd_sign_smb3_pdu(conn, signing_algorithm, signing_key, iov, 1,
+ signature);
if (crypto_memneq(signature, signature_req, SMB2_SIGNATURE_SIZE)) {
pr_err("bad smb2 signature\n");
@@ -12987,6 +12997,7 @@ void smb3_set_sign_rsp(struct ksmbd_work *work)
u16 command;
int n_vec;
char *signing_key;
+ __le16 signing_algorithm;
hdr = ksmbd_resp_buf_curr(work);
command = le16_to_cpu(hdr->Command);
@@ -12994,12 +13005,14 @@ void smb3_set_sign_rsp(struct ksmbd_work *work)
if (command == SMB2_SESSION_SETUP_HE &&
(!work->session_setup_binding || hdr->Status != STATUS_SUCCESS)) {
signing_key = work->sess->smb3signingkey;
+ signing_algorithm = work->sess->signing_algorithm;
} else {
chann = lookup_chann_list(work->sess, work->conn);
if (!chann) {
return;
}
signing_key = chann->smb3signingkey;
+ signing_algorithm = conn->signing_algorithm;
}
if (!signing_key)
@@ -13010,7 +13023,8 @@ void smb3_set_sign_rsp(struct ksmbd_work *work)
iov = smb2_get_sign_rsp_iov(work, hdr, &n_vec);
- ksmbd_sign_smb3_pdu(conn, signing_key, iov, n_vec, signature);
+ ksmbd_sign_smb3_pdu(conn, signing_algorithm, signing_key, iov, n_vec,
+ signature);
memcpy(hdr->Signature, signature, SMB2_SIGNATURE_SIZE);
}
--
2.43.0
^ permalink raw reply [flat|nested] 4+ messages in thread* [PATCH 2/2] ksmbd: add AES-GMAC signing support
2026-11-03 11:14 [PATCH 0/2] ksmbd: AES-GMAC signing support Michail Andreas Michalopoulos
2026-11-03 11:14 ` [PATCH 1/2] ksmbd: sign with the negotiated SMB 3.1.1 signing algorithm Michail Andreas Michalopoulos
@ 2026-11-03 11:14 ` Michail Andreas Michalopoulos
2026-11-03 17:17 ` Ian Bridges
1 sibling, 1 reply; 4+ messages in thread
From: Michail Andreas Michalopoulos @ 2026-11-03 11:14 UTC (permalink / raw)
To: Namjae Jeon
Cc: Michail Andreas Michalopoulos, Sergey Senozhatsky, Tom Talpey,
ChenXiaoSong, Enzo Matsumiya, linux-cifs, linux-doc,
linux-kernel
SMB 3.1.1 adds AES-GMAC as a signing algorithm that clients can
negotiate in the SMB2_SIGNING_CAPABILITIES context (MS-SMB2 3.1.4.1).
Windows and Samba support it.
Implement it with the AES-GCM library: the message, with its Signature
field zeroed, is authenticated as associated data with nothing
encrypted, and the 16-byte tag is the signature. The 12-byte nonce is
the MessageId followed by a 32-bit value with bit 0 set for messages
from the server and bit 1 set for SMB2 CANCEL.
Also accept AES-GMAC from the client's list of algorithms, and refuse
to bind a channel to a session if only one of them uses AES-GMAC, with
the same status codes as Windows (checked by smbtorture's
smb2.session.bind_negative_smb3sign* tests): STATUS_REQUEST_OUT_OF_SEQUENCE
for an AES-GMAC session and STATUS_NOT_SUPPORTED for an AES-GMAC
channel. These responses keep the SMB2_FLAGS_SIGNED flag like the other
binding errors, as clients reject unsigned responses to signed requests.
Mark the feature as supported in the ksmbd feature status table.
The nonce format follows Enzo Matsumiya's AES-GMAC series for the SMB
client and Samba's implementation.
An AI assistant was used to draft the patch and as an independent
reviewer. Testing is described in the cover letter.
Signed-off-by: Michail Andreas Michalopoulos <mike.michalo@gmail.com>
---
Documentation/filesystems/smb/ksmbd.rst | 2 +-
fs/smb/server/Kconfig | 1 +
fs/smb/server/auth.c | 46 +++++++++++++++++++++++++
fs/smb/server/smb2pdu.c | 35 +++++++++++++++++--
4 files changed, 80 insertions(+), 4 deletions(-)
diff --git a/Documentation/filesystems/smb/ksmbd.rst b/Documentation/filesystems/smb/ksmbd.rst
index 728cfca1320..59c98c53d78 100644
--- a/Documentation/filesystems/smb/ksmbd.rst
+++ b/Documentation/filesystems/smb/ksmbd.rst
@@ -118,7 +118,7 @@ SMB3.1.1 Compression Supported.
SMB3.1.1 over QUIC Planned for future.
Signing over RDMA Under development.
Encryption over RDMA Supported.
-SMB3.1.1 GMAC signing support Planned for future.
+SMB3.1.1 GMAC signing support Supported.
============================== =================================================
diff --git a/fs/smb/server/Kconfig b/fs/smb/server/Kconfig
index f8b03605db5..30523ca165e 100644
--- a/fs/smb/server/Kconfig
+++ b/fs/smb/server/Kconfig
@@ -8,6 +8,7 @@ config SMB_SERVER
select NLS_UCS2_UTILS
select CRYPTO
select CRYPTO_LIB_AES_CBC_MACS
+ select CRYPTO_LIB_AES_GCM
select CRYPTO_LIB_ARC4
select CRYPTO_LIB_MD5
select CRYPTO_LIB_SHA256
diff --git a/fs/smb/server/auth.c b/fs/smb/server/auth.c
index 78e35f21746..f650bdd0beb 100644
--- a/fs/smb/server/auth.c
+++ b/fs/smb/server/auth.c
@@ -13,6 +13,7 @@
#include <linux/xattr.h>
#include <crypto/aead.h>
#include <crypto/aes-cbc-macs.h>
+#include <crypto/aes-gcm.h>
#include <crypto/md5.h>
#include <crypto/sha2.h>
#include <crypto/utils.h>
@@ -501,6 +502,46 @@ void ksmbd_sign_smb2_pdu(struct ksmbd_conn *conn, char *key, struct kvec *iov,
hmac_sha256_final(&ctx, sig);
}
+/*
+ * AES-GMAC signing (SMB 3.1.1, MS-SMB2 3.1.4.1): AES-128-GCM with the
+ * whole message as associated data and nothing encrypted. The nonce is
+ * the MessageId followed by a 32-bit word whose bit 0 is set for messages
+ * from the server and bit 1 for SMB2 CANCEL.
+ */
+static void ksmbd_sign_smb3_pdu_gmac(char *key, struct kvec *iov, int n_vec,
+ char *sig)
+{
+ struct smb2_hdr *hdr = iov[0].iov_base;
+ struct aes_gcm_key gcm_key;
+ struct aes_gcm_ctx gcm_ctx;
+ struct {
+ __le64 mid;
+ __le32 flags;
+ } __packed nonce;
+ int i;
+
+ static_assert(sizeof(nonce) == GCM_AES_IV_SIZE);
+ nonce.mid = hdr->MessageId;
+ nonce.flags = 0;
+ if (hdr->Flags & SMB2_FLAGS_SERVER_TO_REDIR)
+ nonce.flags |= cpu_to_le32(BIT(0));
+ if (hdr->Command == SMB2_CANCEL)
+ nonce.flags |= cpu_to_le32(BIT(1));
+
+ /* This cannot fail, since we always pass valid lengths. */
+ if (WARN_ON_ONCE(aes_gcm_preparekey(&gcm_key, key, SMB3_SIGN_KEY_SIZE,
+ SMB2_SIGNATURE_SIZE))) {
+ memset(sig, 0, SMB2_SIGNATURE_SIZE);
+ return;
+ }
+
+ aes_gcm_init(&gcm_ctx, (const u8 *)&nonce, &gcm_key);
+ for (i = 0; i < n_vec; i++)
+ aes_gcm_auth_update(&gcm_ctx, iov[i].iov_base, iov[i].iov_len);
+ aes_gcm_encrypt_final(&gcm_ctx, sig);
+ memzero_explicit(&gcm_key, sizeof(gcm_key));
+}
+
/**
* ksmbd_sign_smb3_pdu() - function to generate packet signing
* @conn: connection
@@ -518,6 +559,11 @@ void ksmbd_sign_smb3_pdu(struct ksmbd_conn *conn, __le16 signing_algorithm,
struct aes_cmac_ctx cmac_ctx;
int i;
+ if (signing_algorithm == SIGNING_ALG_AES_GMAC_LE) {
+ ksmbd_sign_smb3_pdu_gmac(key, iov, n_vec, sig);
+ return;
+ }
+
if (signing_algorithm == SIGNING_ALG_HMAC_SHA256_LE) {
u8 mac[SHA256_DIGEST_SIZE];
diff --git a/fs/smb/server/smb2pdu.c b/fs/smb/server/smb2pdu.c
index 11994e6b92e..1f977741f30 100644
--- a/fs/smb/server/smb2pdu.c
+++ b/fs/smb/server/smb2pdu.c
@@ -1793,7 +1793,8 @@ static void decode_sign_cap_ctxt(struct ksmbd_conn *conn,
for (i = 0; i < sign_algo_cnt; i++) {
if (pneg_ctxt->SigningAlgorithms[i] == SIGNING_ALG_HMAC_SHA256_LE ||
- pneg_ctxt->SigningAlgorithms[i] == SIGNING_ALG_AES_CMAC_LE) {
+ pneg_ctxt->SigningAlgorithms[i] == SIGNING_ALG_AES_CMAC_LE ||
+ pneg_ctxt->SigningAlgorithms[i] == SIGNING_ALG_AES_GMAC_LE) {
ksmbd_debug(SMB, "Signing Algorithm ID = 0x%x\n",
pneg_ctxt->SigningAlgorithms[i]);
conn->signing_negotiated = true;
@@ -2558,6 +2559,23 @@ static int krb5_authenticate(struct ksmbd_work *work,
}
#endif
+/*
+ * A channel can only be bound to a session signed with AES-GMAC if it
+ * negotiated AES-GMAC too, and the other way round. The status codes are
+ * the ones Windows returns, as checked by smbtorture.
+ */
+static int smb2_check_binding_signing_algorithm(struct ksmbd_conn *conn,
+ struct ksmbd_session *sess)
+{
+ if (sess->signing_algorithm == conn->signing_algorithm)
+ return 0;
+ if (sess->signing_algorithm == SIGNING_ALG_AES_GMAC_LE)
+ return -EPROTO;
+ if (conn->signing_algorithm == SIGNING_ALG_AES_GMAC_LE)
+ return -EOPNOTSUPP;
+ return 0;
+}
+
int smb2_sess_setup(struct ksmbd_work *work)
{
struct ksmbd_conn *conn = work->conn;
@@ -2615,6 +2633,10 @@ int smb2_sess_setup(struct ksmbd_work *work)
goto out_err;
}
+ rc = smb2_check_binding_signing_algorithm(conn, sess);
+ if (rc)
+ goto out_err;
+
if (conn->dialect != sess->dialect) {
rc = -EINVAL;
goto out_err;
@@ -2677,10 +2699,12 @@ int smb2_sess_setup(struct ksmbd_work *work)
} else if ((conn->dialect < SMB30_PROT_ID ||
server_conf.flags & KSMBD_GLOBAL_FLAG_SMB3_MULTICHANNEL) &&
(req->Flags & SMB2_SESSION_REQ_FLAG_BINDING)) {
+ rc = 0;
sess = ksmbd_session_lookup_slowpath(le64_to_cpu(req->hdr.SessionId));
if (sess) {
int sign_ret;
+ rc = smb2_check_binding_signing_algorithm(conn, sess);
work->sess = sess;
installed = true;
if (sess->dialect >= SMB30_PROT_ID)
@@ -2695,7 +2719,8 @@ int smb2_sess_setup(struct ksmbd_work *work)
sess = NULL;
}
}
- rc = -EACCES;
+ if (!rc)
+ rc = -EACCES;
goto out_err;
} else {
sess = ksmbd_session_lookup(conn,
@@ -2823,12 +2848,16 @@ int smb2_sess_setup(struct ksmbd_work *work)
rsp->hdr.Status = STATUS_INSUFFICIENT_RESOURCES;
else if (rc == -EOPNOTSUPP)
rsp->hdr.Status = STATUS_NOT_SUPPORTED;
+ else if (rc == -EPROTO)
+ rsp->hdr.Status = STATUS_REQUEST_OUT_OF_SEQUENCE;
else if (rc == -EKEYREJECTED)
rsp->hdr.Status = STATUS_ACCESS_DENIED;
else if (rc)
rsp->hdr.Status = STATUS_LOGON_FAILURE;
if ((rsp->hdr.Status == STATUS_USER_SESSION_DELETED ||
- (rsp->hdr.Status == STATUS_INVALID_PARAMETER &&
+ ((rsp->hdr.Status == STATUS_INVALID_PARAMETER ||
+ rsp->hdr.Status == STATUS_NOT_SUPPORTED ||
+ rsp->hdr.Status == STATUS_REQUEST_OUT_OF_SEQUENCE) &&
(req->Flags & SMB2_SESSION_REQ_FLAG_BINDING))) &&
(req->hdr.Flags & SMB2_FLAGS_SIGNED))
rsp->hdr.Flags |= SMB2_FLAGS_SIGNED;
--
2.43.0
^ permalink raw reply [flat|nested] 4+ messages in thread