SMB3: Add support for multidialect negotiate (SMB2.1 and later)

With the need to discourage use of less secure dialect, SMB1 (CIFS),
we temporarily upgraded the dialect to SMB3 in 4.13, but since there
are various servers which only support SMB2.1 (2.1 is more secure
than CIFS/SMB1) but not optimal for a default dialect - add support
for multidialect negotiation.  cifs.ko will now request SMB2.1
or later (ie SMB2.1 or SMB3.0, SMB3.02) and the server will
pick the latest most secure one it can support.

In addition since we are sending multidialect negotiate, add
support for secure negotiate to validate that a man in the
middle didn't downgrade us.

Signed-off-by: Steve French <smfrench@gmail.com>
Reviewed-by: Pavel Shilovsky <pshilov@microsoft.com>
CC: Stable <stable@vger.kernel.org> # 4.13+

1 files changed, 17 insertions, 7 deletions

diff --git a/fs/cifs/connect.c b/fs/cifs/connect.c
index 5aa2d278ca84..8d38b22afb2b 100644
--- a/fs/cifs/connect.c
+++ b/fs/cifs/connect.c
@@ -301,6 +301,8 @@ static const match_table_t cifs_smb_version_tokens = {
 	{ Smb_311, SMB311_VERSION_STRING },
 	{ Smb_311, ALT_SMB311_VERSION_STRING },
 #endif /* SMB311 */
+	{ Smb_3any, SMB3ANY_VERSION_STRING },
+	{ Smb_default, SMBDEFAULT_VERSION_STRING },
 	{ Smb_version_err, NULL }
 };
 
@@ -1148,6 +1150,14 @@ cifs_parse_smb_version(char *value, struct smb_vol *vol)
 		vol->vals = &smb311_values;
 		break;
 #endif /* SMB311 */
+	case Smb_3any:
+		vol->ops = &smb30_operations; /* currently identical with 3.0 */
+		vol->vals = &smb3any_values;
+		break;
+	case Smb_default:
+		vol->ops = &smb30_operations; /* currently identical with 3.0 */
+		vol->vals = &smbdefault_values;
+		break;
 	default:
 		cifs_dbg(VFS, "Unknown vers= option specified: %s\n", value);
 		return 1;
@@ -1274,9 +1284,9 @@ cifs_parse_mount_options(const char *mountdata, const char *devname,
 
 	vol->actimeo = CIFS_DEF_ACTIMEO;
 
-	/* FIXME: add autonegotiation for SMB3 or later rather than just SMB3 */
-	vol->ops = &smb30_operations; /* both secure and accepted widely */
-	vol->vals = &smb30_values;
+	/* offer SMB2.1 and later (SMB3 etc). Secure and widely accepted */
+	vol->ops = &smb30_operations;
+	vol->vals = &smbdefault_values;
 
 	vol->echo_interval = SMB_ECHO_INTERVAL_DEFAULT;
 
@@ -1988,11 +1998,10 @@ cifs_parse_mount_options(const char *mountdata, const char *devname,
 
 	if (got_version == false)
 		pr_warn("No dialect specified on mount. Default has changed to "
-			"a more secure dialect, SMB3 (vers=3.0), from CIFS "
+			"a more secure dialect, SMB2.1 or later (e.g. SMB3), from CIFS "
 			"(SMB1). To use the less secure SMB1 dialect to access "
-			"old servers which do not support SMB3 specify vers=1.0"
-			" on mount. For somewhat newer servers such as Windows "
-			"7 try vers=2.1.\n");
+			"old servers which do not support SMB3 (or SMB2.1) specify vers=1.0"
+			" on mount.\n");
 
 	kfree(mountdata_copy);
 	return 0;
@@ -2133,6 +2142,7 @@ static int match_server(struct TCP_Server_Info *server, struct smb_vol *vol)
 	if (vol->nosharesock)
 		return 0;
 
+	/* BB update this for smb3any and default case */
 	if ((server->vals != vol->vals) || (server->ops != vol->ops))
 		return 0;