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

[Michail Andreas Michalopoulos <mike.michalo@gmail.com>]

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