[PATCH] ksmbd: add buffer validation in session setup

[Marios Makassikis <mmakassikis@xxxxxxxxxx>]

Make sure the security buffer's length/offset are valid with regards to
the packet length.

Signed-off-by: Marios Makassikis <mmakassikis@xxxxxxxxxx>
---
 fs/ksmbd/smb2pdu.c | 51 ++++++++++++++++++++++++++++------------------
 1 file changed, 31 insertions(+), 20 deletions(-)

diff --git a/fs/ksmbd/smb2pdu.c b/fs/ksmbd/smb2pdu.c
index 005aa93a49d6..5fc766439f0f 100644
--- a/fs/ksmbd/smb2pdu.c
+++ b/fs/ksmbd/smb2pdu.c
@@ -1274,19 +1274,13 @@ static int generate_preauth_hash(struct ksmbd_work *work)
 	return 0;
 }
 
-static int decode_negotiation_token(struct ksmbd_work *work,
-				    struct negotiate_message *negblob)
+static int decode_negotiation_token(struct ksmbd_conn *conn,
+				    struct negotiate_message *negblob,
+				    size_t sz)
 {
-	struct ksmbd_conn *conn = work->conn;
-	struct smb2_sess_setup_req *req;
-	int sz;
-
 	if (!conn->use_spnego)
 		return -EINVAL;
 
-	req = work->request_buf;
-	sz = le16_to_cpu(req->SecurityBufferLength);
-
 	if (ksmbd_decode_negTokenInit((char *)negblob, sz, conn)) {
 		if (ksmbd_decode_negTokenTarg((char *)negblob, sz, conn)) {
 			conn->auth_mechs |= KSMBD_AUTH_NTLMSSP;
@@ -1298,9 +1292,9 @@ static int decode_negotiation_token(struct ksmbd_work *work,
 }
 
 static int ntlm_negotiate(struct ksmbd_work *work,
-			  struct negotiate_message *negblob)
+			  struct negotiate_message *negblob,
+			  size_t negblob_len)
 {
-	struct smb2_sess_setup_req *req = work->request_buf;
 	struct smb2_sess_setup_rsp *rsp = work->response_buf;
 	struct challenge_message *chgblob;
 	unsigned char *spnego_blob = NULL;
@@ -1309,8 +1303,7 @@ static int ntlm_negotiate(struct ksmbd_work *work,
 	int sz, rc;
 
 	ksmbd_debug(SMB, "negotiate phase\n");
-	sz = le16_to_cpu(req->SecurityBufferLength);
-	rc = ksmbd_decode_ntlmssp_neg_blob(negblob, sz, work->sess);
+	rc = ksmbd_decode_ntlmssp_neg_blob(negblob, negblob_len, work->sess);
 	if (rc)
 		return rc;
 
@@ -1378,12 +1371,20 @@ static struct ksmbd_user *session_user(struct ksmbd_conn *conn,
 	struct authenticate_message *authblob;
 	struct ksmbd_user *user;
 	char *name;
-	int sz;
+	unsigned int name_off, name_len, pdu_len;
 
 	authblob = user_authblob(conn, req);
-	sz = le32_to_cpu(authblob->UserName.BufferOffset);
-	name = smb_strndup_from_utf16((const char *)authblob + sz,
-				      le16_to_cpu(authblob->UserName.Length),
+	pdu_len = get_rfc1002_len(req) + 4;
+	name_off = le32_to_cpu(authblob->UserName.BufferOffset);
+	name_len = le16_to_cpu(authblob->UserName.Length);
+
+	if (((char *)authblob + name_off > (char *)req + pdu_len) ||
+	    (sizeof(struct smb2_sess_setup_req) +
+	    sizeof(struct authenticate_message) + name_len > pdu_len))
+		return NULL;
+
+	name = smb_strndup_from_utf16((const char *)authblob + name_off,
+				      name_len,
 				      true,
 				      conn->local_nls);
 	if (IS_ERR(name)) {
@@ -1629,6 +1630,7 @@ int smb2_sess_setup(struct ksmbd_work *work)
 	struct smb2_sess_setup_rsp *rsp = work->response_buf;
 	struct ksmbd_session *sess;
 	struct negotiate_message *negblob;
+	unsigned int pdu_length, negblob_len, negblob_off;
 	int rc = 0;
 
 	ksmbd_debug(SMB, "Received request for session setup\n");
@@ -1709,10 +1711,19 @@ int smb2_sess_setup(struct ksmbd_work *work)
 	if (sess->state == SMB2_SESSION_EXPIRED)
 		sess->state = SMB2_SESSION_IN_PROGRESS;
 
+	pdu_length = get_rfc1002_len(req);
+	negblob_off = le16_to_cpu(req->SecurityBufferOffset);
+	negblob_len = le16_to_cpu(req->SecurityBufferLength);
+	if (negblob_off != (offsetof(struct smb2_sess_setup_req, Buffer) - 4))
+		return -EINVAL;
+
+	/* account for Buffer[1] and smb2_buf_length */
+	if (sizeof(struct smb2_sess_setup_req) + negblob_len - 1 > pdu_length + 4)
+		return -EINVAL;
 	negblob = (struct negotiate_message *)((char *)&req->hdr.ProtocolId +
-			le16_to_cpu(req->SecurityBufferOffset));
+			negblob_off);
 
-	if (decode_negotiation_token(work, negblob) == 0) {
+	if (decode_negotiation_token(conn, negblob, negblob_len) == 0) {
 		if (conn->mechToken)
 			negblob = (struct negotiate_message *)conn->mechToken;
 	}
@@ -1736,7 +1747,7 @@ int smb2_sess_setup(struct ksmbd_work *work)
 			sess->Preauth_HashValue = NULL;
 		} else if (conn->preferred_auth_mech == KSMBD_AUTH_NTLMSSP) {
 			if (negblob->MessageType == NtLmNegotiate) {
-				rc = ntlm_negotiate(work, negblob);
+				rc = ntlm_negotiate(work, negblob, negblob_len);
 				if (rc)
 					goto out_err;
 				rsp->hdr.Status =
-- 
2.25.1