linux-kernel - [PATCH 4.14 60/63] cifs: allow disabling insecure dialects in the config

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Date:   Thu, 24 Jan 2019 20:20:49 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Steve French <stfrench@...rosoft.com>,
        Aurelien Aptel <aaptel@...e.com>,
        Jeremy Allison <jra@...ba.org>,
        Alakesh Haloi <alakeshh@...zon.com>
Subject: [PATCH 4.14 60/63] cifs: allow disabling insecure dialects in the config

4.14-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Steve French <stfrench@...rosoft.com>

commit 7420451f6a109f7f8f1bf283f34d08eba3259fb3 upstream.

allow disabling cifs (SMB1 ie vers=1.0) and vers=2.0 in the
config for the build of cifs.ko if want to always prevent mounting
with these less secure dialects.

Signed-off-by: Steve French <stfrench@...rosoft.com>
Reviewed-by: Aurelien Aptel <aaptel@...e.com>
Reviewed-by: Jeremy Allison <jra@...ba.org>
Cc: Alakesh Haloi <alakeshh@...zon.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 fs/cifs/Kconfig   |   17 ++++++++++++++++-
 fs/cifs/connect.c |    9 +++++++++
 2 files changed, 25 insertions(+), 1 deletion(-)

--- a/fs/cifs/Kconfig
+++ b/fs/cifs/Kconfig
@@ -66,9 +66,24 @@ config CIFS_STATS2
 	  Unless you are a developer or are doing network performance analysis
 	  or tuning, say N.
 
+config CIFS_ALLOW_INSECURE_LEGACY
+	bool "Support legacy servers which use less secure dialects"
+	depends on CIFS
+	default y
+	help
+	  Modern dialects, SMB2.1 and later (including SMB3 and 3.1.1), have
+	  additional security features, including protection against
+	  man-in-the-middle attacks and stronger crypto hashes, so the use
+	  of legacy dialects (SMB1/CIFS and SMB2.0) is discouraged.
+
+	  Disabling this option prevents users from using vers=1.0 or vers=2.0
+	  on mounts with cifs.ko
+
+	  If unsure, say Y.
+
 config CIFS_WEAK_PW_HASH
 	bool "Support legacy servers which use weaker LANMAN security"
-	depends on CIFS
+	depends on CIFS && CIFS_ALLOW_INSECURE_LEGACY
 	help
 	  Modern CIFS servers including Samba and most Windows versions
 	  (since 1997) support stronger NTLM (and even NTLMv2 and Kerberos)
--- a/fs/cifs/connect.c
+++ b/fs/cifs/connect.c
@@ -1130,6 +1130,7 @@ cifs_parse_smb_version(char *value, stru
 	substring_t args[MAX_OPT_ARGS];
 
 	switch (match_token(value, cifs_smb_version_tokens, args)) {
+#ifdef CONFIG_CIFS_ALLOW_INSECURE_LEGACY
 	case Smb_1:
 		vol->ops = &smb1_operations;
 		vol->vals = &smb1_values;
@@ -1138,6 +1139,14 @@ cifs_parse_smb_version(char *value, stru
 		vol->ops = &smb20_operations;
 		vol->vals = &smb20_values;
 		break;
+#else
+	case Smb_1:
+		cifs_dbg(VFS, "vers=1.0 (cifs) mount not permitted when legacy dialects disabled\n");
+		return 1;
+	case Smb_20:
+		cifs_dbg(VFS, "vers=2.0 mount not permitted when legacy dialects disabled\n");
+		return 1;
+#endif /* CIFS_ALLOW_INSECURE_LEGACY */
 	case Smb_21:
 		vol->ops = &smb21_operations;
 		vol->vals = &smb21_values;