From 5100d8a3fe034845926266a4e7f5bdcbb859088b Mon Sep 17 00:00:00 2001
From: Steve French <smfrench@gmail.com>
Date: Mon, 9 Apr 2018 10:47:14 -0500
Subject: [PATCH] SMB311: Improve checking of negotiate security contexts
Git-commit: 5100d8a3fe034845926266a4e7f5bdcbb859088b
Patch-mainline: v4.17-rc1
References: bsc#1051510, bsc#1144333

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>
Acked-by: Paulo Alcantara <palcantara@suse.de>
---
 fs/cifs/cifsglob.h |   1 +
 fs/cifs/smb2pdu.c  | 102 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 fs/cifs/smb2pdu.h  |   3 ++
 3 files changed, 106 insertions(+)

diff --git a/fs/cifs/cifsglob.h b/fs/cifs/cifsglob.h
index 2282562e78a1..56fee0330afc 100644
--- a/fs/cifs/cifsglob.h
+++ b/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 */
diff --git a/fs/cifs/smb2pdu.c b/fs/cifs/smb2pdu.c
index 6c2910e6c984..e01be06d588e 100644
--- a/fs/cifs/smb2pdu.c
+++ b/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;
diff --git a/fs/cifs/smb2pdu.h b/fs/cifs/smb2pdu.h
index 0e0a0af89e4d..6093e5142b2b 100644
--- a/fs/cifs/smb2pdu.h
+++ b/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;
-- 
2.16.4