[PATCH 0/2] ksmbd: AES-GMAC signing support

[PATCH 0/2] ksmbd: AES-GMAC signing support

[Michail Andreas Michalopoulos]

SMB 3.1.1 clients choose the signing algorithm in the
SMB2_SIGNING_CAPABILITIES negotiate context. ksmbd parses the client's
list, but init_smb3_11_server() then overwrites the choice with
AES-CMAC, so a client that does not offer AES-CMAC cannot connect.
Patch 1 fixes that and keeps each signing key paired with the
algorithm it was created for. Patch 2 adds AES-GMAC, which Windows and
macOS offer first, using the lib/crypto AES-GCM API.

Discussion:
https://lore.kernel.org/linux-cifs/D0F05F9A-5097-4A2D-9235-AE395961F456@gmail.com/

Testing:
- smbtorture 4.19 with each algorithm forced
  (clientsmb3signingalgorithms): without the series an HMAC-SHA256
  only client fails smb2.connect with NT_STATUS_INVALID_NETWORK_RESPONSE
  and an AES-GMAC only client cannot negotiate. With it, all three
  connect and sign with the forced algorithm; smb2.connect then stops
  at its tree disconnect check (STATUS_ACCESS_DENIED instead of
  STATUS_NETWORK_NAME_DELETED), as it does for AES-CMAC without the
  series.
- smb2.session (smbtorture 4.19, multichannel off): 21 tests pass
  instead of 12. signing-hmac-sha-256, signing-aes-128-cmac,
  signing-aes-128-gmac, encryption-aes-{128,256}-{ccm,gcm} and
  bind_negative_smb3signGtoH2X{d,s} need signing negotiation and now
  run and pass instead of being skipped. 26 other
  bind_negative_smb3sign*/smb3sne* tests now run too and fail with
  STATUS_USER_SESSION_DELETED, because binding needs multichannel;
  see the next item for them with multichannel enabled. No test that
  passed before fails.
- smb2.bench.echo and smb2.bench.read with each algorithm forced,
  smbtorture 4.19 (x86) and 4.23 (arm64).
- smb2.session.bind_negative* with multichannel enabled (smbtorture
  4.19): all tests involving AES-GMAC pass. Without the series most
  smb3sign* tests were skipped, as ksmbd could not negotiate anything
  but AES-CMAC. The four AES-CMAC <-> HMAC-SHA256 tests now run and
  fail on existing binding behaviour that this series does not touch:
  the *d variants because ksmbd rejects binding from a different
  ClientGUID (Windows accepts it), the *s variants because a session
  setup without the binding flag on an already bound connection
  succeeds instead of failing with STATUS_ACCESS_DENIED.
- Windows Server 2025: offered AES-GMAC, AES-CMAC, HMAC-SHA256 and
  ksmbd answered AES-GMAC (checked in a packet capture). A 1 GiB copy
  to and from the share came back identical (SHA256), with signing
  required and encryption off.
- macOS 26: negotiated AES-GMAC, 256 MiB copy identical.
- No "bad smb2 signature" messages in any of these runs.

End to end, smbtorture smb2.bench.read with 1 MiB reads, MB/s:

                               HMAC-SHA256   AES-CMAC   AES-GMAC
  arm64, Apple M4 VM, loopback        1354        924        797
  x86, AMD EPYC VMs, 3.56 Gbit/s       449        341        469

On arm64 AES-GMAC is currently the slowest because the arm64 GHASH
library code does not use PMULL for bulk data; I'll send a separate
lib/crypto series for that, as discussed in the thread above.

Not tested: multichannel with Windows or macOS clients (binding was
only tested with smbtorture), and SMB over RDMA.

An AI assistant was used to draft the patches and as an independent
reviewer. I ran the Windows, macOS and benchmark tests; the smbtorture
runs were done by the assistant under UML.

Michail Andreas Michalopoulos (2):
  ksmbd: sign with the negotiated SMB 3.1.1 signing algorithm
  ksmbd: add AES-GMAC signing support

 Documentation/filesystems/smb/ksmbd.rst |  2 +-
 fs/smb/server/Kconfig                   |  1 +
 fs/smb/server/auth.c                    | 60 ++++++++++++++++++++++++-
 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                 | 53 +++++++++++++++++++---
 8 files changed, 116 insertions(+), 11 deletions(-)


base-commit: af8c72f6550744fe948ef2dbc7ab8739c149aab2
-- 
2.43.0

[PATCH 1/2] ksmbd: sign with the negotiated SMB 3.1.1 signing algorithm

[Michail Andreas Michalopoulos]

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

[PATCH 2/2] ksmbd: add AES-GMAC signing support

[Michail Andreas Michalopoulos]

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

Re: [PATCH 2/2] ksmbd: add AES-GMAC signing support

[Ian Bridges]

Hi Michail,

With patch 2, an existing gap in SMB3 binding request verification
leads to AES-GMAC nonce reuse. It needs
"server multi channel support = yes", which is disabled by default.

In the multichannel branch of smb2_sess_setup(), ksmbd checks that
SMB2_FLAGS_SIGNED is present but does not verify the request with the
existing Session.SigningKey, as MS-SMB2 3.3.5.2.4 requires. The request
can then reach authentication processing, and a non-success
SESSION_SETUP response is signed with that session key.

I reproduced this with multichannel enabled and AES-GMAC negotiated.
Three new connections sent binding SESSION_SETUP requests for an
existing session, each with MessageId 1 and a random signature. All
three returned STATUS_MORE_PROCESSING_REQUIRED. Each response was
signed with the existing session's key and used the nonce
010000000000000001000000.

The responses contained different NTLM challenges, so distinct
messages were authenticated with the same AES-GMAC key and nonce.

This violates GMAC's nonce-uniqueness requirement (NIST SP 800-38D).
The same test with AES-CMAC confirms the pre-existing signing oracle,
but does not create the GMAC nonce-reuse problem.

The probe also recovers the GHASH key from four of these responses,
two pairs of different lengths, without the signing key. With the
GHASH key and one more response, it computes a tag for a different
message at MessageId 7 that verifies under the session's signing key.
A single connection reaches other MessageIds by stepping through the
credits the server grants, 64 per response.

Could the binding request be verified with Session.SigningKey before
it is processed or any response is signed with that key?

Thanks,
Ian

Re: [PATCH 2/2] ksmbd: add AES-GMAC signing support

[mixalhs]

Hi Ian,
Thank you for the careful analysis and the reproducer. 

You’re right: in the multichannel branch of smb2_sess_setup() the binding 
request is never verified with Session.SigningKey, and with AES-GMAC t
hat turns the existing signing oracle into nonce reuse.
Namjae, please don’t apply this version. I was unaware of this.
I’ll send a v2 that first verifies binding requests with the session signing 
key before they are processed or any response is signed with it, and 
check whether legitimate binding can also reuse a nonce under 
the session key.
Thanks,

Michalis