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, 75 insertions, 10 deletions

diff --git a/fs/cifs/smb2pdu.c b/fs/cifs/smb2pdu.c
index 69a751b038ab..5c16591a128e 100644
--- a/fs/cifs/smb2pdu.c
+++ b/fs/cifs/smb2pdu.c
@@ -491,10 +491,25 @@ SMB2_negotiate(const unsigned int xid, struct cifs_ses *ses)
 
 	req->hdr.sync_hdr.SessionId = 0;
 
-	req->Dialects[0] = cpu_to_le16(ses->server->vals->protocol_id);
-
-	req->DialectCount = cpu_to_le16(1); /* One vers= at a time for now */
-	inc_rfc1001_len(req, 2);
+	if (strcmp(ses->server->vals->version_string,
+		   SMB3ANY_VERSION_STRING) == 0) {
+		req->Dialects[0] = cpu_to_le16(SMB30_PROT_ID);
+		req->Dialects[1] = cpu_to_le16(SMB302_PROT_ID);
+		req->DialectCount = cpu_to_le16(2);
+		inc_rfc1001_len(req, 4);
+	} else if (strcmp(ses->server->vals->version_string,
+		   SMBDEFAULT_VERSION_STRING) == 0) {
+		req->Dialects[0] = cpu_to_le16(SMB21_PROT_ID);
+		req->Dialects[1] = cpu_to_le16(SMB30_PROT_ID);
+		req->Dialects[2] = cpu_to_le16(SMB302_PROT_ID);
+		req->DialectCount = cpu_to_le16(3);
+		inc_rfc1001_len(req, 6);
+	} else {
+		/* otherwise send specific dialect */
+		req->Dialects[0] = cpu_to_le16(ses->server->vals->protocol_id);
+		req->DialectCount = cpu_to_le16(1);
+		inc_rfc1001_len(req, 2);
+	}
 
 	/* only one of SMB2 signing flags may be set in SMB2 request */
 	if (ses->sign)
@@ -528,16 +543,42 @@ SMB2_negotiate(const unsigned int xid, struct cifs_ses *ses)
 	 */
 	if (rc == -EOPNOTSUPP) {
 		cifs_dbg(VFS, "Dialect not supported by server. Consider "
-			"specifying vers=1.0 or vers=2.1 on mount for accessing"
+			"specifying vers=1.0 or vers=2.0 on mount for accessing"
 			" older servers\n");
 		goto neg_exit;
 	} else if (rc != 0)
 		goto neg_exit;
 
+	if (strcmp(ses->server->vals->version_string,
+		   SMB3ANY_VERSION_STRING) == 0) {
+		if (rsp->DialectRevision == cpu_to_le16(SMB20_PROT_ID)) {
+			cifs_dbg(VFS,
+				"SMB2 dialect returned but not requested\n");
+			return -EIO;
+		} else if (rsp->DialectRevision == cpu_to_le16(SMB21_PROT_ID)) {
+			cifs_dbg(VFS,
+				"SMB2.1 dialect returned but not requested\n");
+			return -EIO;
+		}
+	} else if (strcmp(ses->server->vals->version_string,
+		   SMBDEFAULT_VERSION_STRING) == 0) {
+		if (rsp->DialectRevision == cpu_to_le16(SMB20_PROT_ID)) {
+			cifs_dbg(VFS,
+				"SMB2 dialect returned but not requested\n");
+			return -EIO;
+		} else if (rsp->DialectRevision == cpu_to_le16(SMB21_PROT_ID)) {
+			/* ops set to 3.0 by default for default so update */
+			ses->server->ops = &smb21_operations;
+		}
+	} else if (rsp->DialectRevision != ses->server->vals->protocol_id) {
+		/* if requested single dialect ensure returned dialect matched */
+		cifs_dbg(VFS, "Illegal 0x%x dialect returned: not requested\n",
+			cpu_to_le16(rsp->DialectRevision));
+		return -EIO;
+	}
+
 	cifs_dbg(FYI, "mode 0x%x\n", rsp->SecurityMode);
 
-	/* BB we may eventually want to match the negotiated vs. requested
-	   dialect, even though we are only requesting one at a time */
 	if (rsp->DialectRevision == cpu_to_le16(SMB20_PROT_ID))
 		cifs_dbg(FYI, "negotiated smb2.0 dialect\n");
 	else if (rsp->DialectRevision == cpu_to_le16(SMB21_PROT_ID))
@@ -558,6 +599,8 @@ SMB2_negotiate(const unsigned int xid, struct cifs_ses *ses)
 	}
 	server->dialect = le16_to_cpu(rsp->DialectRevision);
 
+	/* BB: add check that dialect was valid given dialect(s) we asked for */
+
 	/* SMB2 only has an extended negflavor */
 	server->negflavor = CIFS_NEGFLAVOR_EXTENDED;
 	/* set it to the maximum buffer size value we can send with 1 credit */
@@ -606,6 +649,7 @@ int smb3_validate_negotiate(const unsigned int xid, struct cifs_tcon *tcon)
 	struct validate_negotiate_info_req vneg_inbuf;
 	struct validate_negotiate_info_rsp *pneg_rsp;
 	u32 rsplen;
+	u32 inbuflen; /* max of 4 dialects */
 
 	cifs_dbg(FYI, "validate negotiate\n");
 
@@ -634,9 +678,30 @@ int smb3_validate_negotiate(const unsigned int xid, struct cifs_tcon *tcon)
 	else
 		vneg_inbuf.SecurityMode = 0;
 
-	vneg_inbuf.DialectCount = cpu_to_le16(1);
-	vneg_inbuf.Dialects[0] =
-		cpu_to_le16(tcon->ses->server->vals->protocol_id);
+
+	if (strcmp(tcon->ses->server->vals->version_string,
+		SMB3ANY_VERSION_STRING) == 0) {
+		vneg_inbuf.Dialects[0] = cpu_to_le16(SMB30_PROT_ID);
+		vneg_inbuf.Dialects[1] = cpu_to_le16(SMB302_PROT_ID);
+		vneg_inbuf.DialectCount = cpu_to_le16(2);
+		/* structure is big enough for 3 dialects, sending only 2 */
+		inbuflen = sizeof(struct validate_negotiate_info_req) - 2;
+	} else if (strcmp(tcon->ses->server->vals->version_string,
+		SMBDEFAULT_VERSION_STRING) == 0) {
+		vneg_inbuf.Dialects[0] = cpu_to_le16(SMB21_PROT_ID);
+		vneg_inbuf.Dialects[1] = cpu_to_le16(SMB30_PROT_ID);
+		vneg_inbuf.Dialects[2] = cpu_to_le16(SMB302_PROT_ID);
+		vneg_inbuf.DialectCount = cpu_to_le16(3);
+		/* structure is big enough for 3 dialects */
+		inbuflen = sizeof(struct validate_negotiate_info_req);
+	} else {
+		/* otherwise specific dialect was requested */
+		vneg_inbuf.Dialects[0] =
+			cpu_to_le16(tcon->ses->server->vals->protocol_id);
+		vneg_inbuf.DialectCount = cpu_to_le16(1);
+		/* structure is big enough for 3 dialects, sending only 1 */
+		inbuflen = sizeof(struct validate_negotiate_info_req) - 4;
+	}
 
 	rc = SMB2_ioctl(xid, tcon, NO_FILE_ID, NO_FILE_ID,
 		FSCTL_VALIDATE_NEGOTIATE_INFO, true /* is_fsctl */,