SMB311: Improve checking of negotiate security contexts

SMB3.11 crypto and hash contexts were not being checked strictly enough.
Add parsing and validity checking for the security contexts in the SMB3.11
negotiate response.
Signed-off-by: Steve French <smfrench@gmail.com>
CC: Stable <stable@vger.kernel.org>
Reviewed-by: Pavel Shilovsky <pshilov@microsoft.com>

fs/cifs/cifsglob.h

@@ -676,6 +676,7 @@ struct TCP_Server_Info {
 	unsigned int	max_read;
 	unsigned int	max_write;
 #ifdef CONFIG_CIFS_SMB311
+	__le16	cipher_type;
 	 /* save initital negprot hash */
 	__u8	preauth_sha_hash[SMB2_PREAUTH_HASH_SIZE];
 #endif /* 3.1.1 */

fs/cifs/smb2pdu.c

@@ -406,6 +406,99 @@ assemble_neg_contexts(struct smb2_negotiate_req *req,
 	*total_len += 4 + sizeof(struct smb2_preauth_neg_context)
 		+ sizeof(struct smb2_encryption_neg_context);
 }
+
+static void decode_preauth_context(struct smb2_preauth_neg_context *ctxt)
+{
+	unsigned int len = le16_to_cpu(ctxt->DataLength);
+
+	/* If invalid preauth context warn but use what we requested, SHA-512 */
+	if (len < MIN_PREAUTH_CTXT_DATA_LEN) {
+		printk_once(KERN_WARNING "server sent bad preauth context\n");
+		return;
+	}
+	if (le16_to_cpu(ctxt->HashAlgorithmCount) != 1)
+		printk_once(KERN_WARNING "illegal SMB3 hash algorithm count\n");
+	if (ctxt->HashAlgorithms != SMB2_PREAUTH_INTEGRITY_SHA512)
+		printk_once(KERN_WARNING "unknown SMB3 hash algorithm\n");
+}
+
+static int decode_encrypt_ctx(struct TCP_Server_Info *server,
+			      struct smb2_encryption_neg_context *ctxt)
+{
+	unsigned int len = le16_to_cpu(ctxt->DataLength);
+
+	cifs_dbg(FYI, "decode SMB3.11 encryption neg context of len %d\n", len);
+	if (len < MIN_ENCRYPT_CTXT_DATA_LEN) {
+		printk_once(KERN_WARNING "server sent bad crypto ctxt len\n");
+		return -EINVAL;
+	}
+
+	if (le16_to_cpu(ctxt->CipherCount) != 1) {
+		printk_once(KERN_WARNING "illegal SMB3.11 cipher count\n");
+		return -EINVAL;
+	}
+	cifs_dbg(FYI, "SMB311 cipher type:%d\n", le16_to_cpu(ctxt->Ciphers[0]));
+	if ((ctxt->Ciphers[0] != SMB2_ENCRYPTION_AES128_CCM) &&
+	    (ctxt->Ciphers[0] != SMB2_ENCRYPTION_AES128_GCM)) {
+		printk_once(KERN_WARNING "invalid SMB3.11 cipher returned\n");
+		return -EINVAL;
+	}
+	server->cipher_type = ctxt->Ciphers[0];
+	return 0;
+}
+
+static int smb311_decode_neg_context(struct smb2_negotiate_rsp *rsp,
+				     struct TCP_Server_Info *server)
+{
+	struct smb2_neg_context *pctx;
+	unsigned int offset = le32_to_cpu(rsp->NegotiateContextOffset);
+	unsigned int ctxt_cnt = le16_to_cpu(rsp->NegotiateContextCount);
+	unsigned int len_of_smb = be32_to_cpu(rsp->hdr.smb2_buf_length);
+	unsigned int len_of_ctxts, i;
+	int rc = 0;
+
+	cifs_dbg(FYI, "decoding %d negotiate contexts\n", ctxt_cnt);
+	if (len_of_smb <= offset) {
+		cifs_dbg(VFS, "Invalid response: negotiate context offset\n");
+		return -EINVAL;
+	}
+
+	len_of_ctxts = len_of_smb - offset;
+
+	for (i = 0; i < ctxt_cnt; i++) {
+		int clen;
+		/* check that offset is not beyond end of SMB */
+		if (len_of_ctxts == 0)
+			break;
+
+		if (len_of_ctxts < sizeof(struct smb2_neg_context))
+			break;
+
+		pctx = (struct smb2_neg_context *)(offset + 4 + (char *)rsp);
+		clen = le16_to_cpu(pctx->DataLength);
+		if (clen > len_of_ctxts)
+			break;
+
+		if (pctx->ContextType == SMB2_PREAUTH_INTEGRITY_CAPABILITIES)
+			decode_preauth_context(
+				(struct smb2_preauth_neg_context *)pctx);
+		else if (pctx->ContextType == SMB2_ENCRYPTION_CAPABILITIES)
+			rc = decode_encrypt_ctx(server,
+				(struct smb2_encryption_neg_context *)pctx);
+		else
+			cifs_dbg(VFS, "unknown negcontext of type %d ignored\n",
+				le16_to_cpu(pctx->ContextType));
+
+		if (rc)
+			break;
+		/* offsets must be 8 byte aligned */
+		clen = (clen + 7) & ~0x7;
+		offset += clen + sizeof(struct smb2_neg_context);
+		len_of_ctxts -= clen;
+	}
+	return rc;
+}
+
 #else
 static void assemble_neg_contexts(struct smb2_negotiate_req *req,
 				  unsigned int *total_len)
@@ -619,6 +712,15 @@ SMB2_negotiate(const unsigned int xid, struct cifs_ses *ses)
 		else if (rc == 0)
 			rc = -EIO;
 	}
+
+#ifdef CONFIG_CIFS_SMB311
+	if (rsp->DialectRevision == cpu_to_le16(SMB311_PROT_ID)) {
+		if (rsp->NegotiateContextCount)
+			rc = smb311_decode_neg_context(rsp, server);
+		else
+			cifs_dbg(VFS, "Missing expected negotiate contexts\n");
+	}
+#endif /* CONFIG_CIFS_SMB311 */
 neg_exit:
 	free_rsp_buf(resp_buftype, rsp);
 	return rc;

fs/cifs/smb2pdu.h

@@ -275,6 +275,7 @@ struct smb2_neg_context {
 #define SMB2_PREAUTH_INTEGRITY_SHA512	cpu_to_le16(0x0001)
 #define SMB2_PREAUTH_HASH_SIZE 64
 
+#define MIN_PREAUTH_CTXT_DATA_LEN	(SMB311_SALT_SIZE + 6)
 struct smb2_preauth_neg_context {
 	__le16	ContextType; /* 1 */
 	__le16	DataLength;
@@ -289,6 +290,8 @@ struct smb2_preauth_neg_context {
 #define SMB2_ENCRYPTION_AES128_CCM	cpu_to_le16(0x0001)
 #define SMB2_ENCRYPTION_AES128_GCM	cpu_to_le16(0x0002)
 
+/* Min encrypt context data is one cipher so 2 bytes + 2 byte count field */
+#define MIN_ENCRYPT_CTXT_DATA_LEN	4
 struct smb2_encryption_neg_context {
 	__le16	ContextType; /* 2 */
 	__le16	DataLength;