cifs: dynamic allocation of ntlmssp blob

commit b8da344b upstream.

In sess_auth_rawntlmssp_authenticate(), the ntlmssp blob is allocated
statically and its size is an "empirical" 5*sizeof(struct
_AUTHENTICATE_MESSAGE) (320B on x86_64). I don't know where this value
comes from or if it was ever appropriate, but it is currently
insufficient: the user and domain name in UTF16 could take 1kB by
themselves. Because of that, build_ntlmssp_auth_blob() might corrupt
memory (out-of-bounds write). The size of ntlmssp_blob in
SMB2_sess_setup() is too small too (sizeof(struct _NEGOTIATE_MESSAGE)
+ 500).

This patch allocates the blob dynamically in
build_ntlmssp_auth_blob().
Signed-off-by: Jerome Marchand <jmarchan@redhat.com>
Signed-off-by: Steve French <smfrench@gmail.com>
[bwh: Backported to 3.2:
 - Adjust context, indentation
 - build_ntlmssp_auth_blob() is static
 - Drop changes to smb2pdu.c
 - Use cERROR() instead of cifs_dbg(VFS, ...)
 - Use MAX_USERNAME_SIZE instead of CIFS_MAX_USERNAME_LEN]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

fs/cifs/sess.c

@@ -444,19 +444,43 @@ static void build_ntlmssp_negotiate_blob(unsigned char *pbuffer,
 	sec_blob->DomainName.MaximumLength = 0;
 }
 
-/* We do not malloc the blob, it is passed in pbuffer, because its
-   maximum possible size is fixed and small, making this approach cleaner.
-   This function returns the length of the data in the blob */
-static int build_ntlmssp_auth_blob(unsigned char *pbuffer,
+static int size_of_ntlmssp_blob(struct cifs_ses *ses)
+{
+	int sz = sizeof(AUTHENTICATE_MESSAGE) + ses->auth_key.len
+		- CIFS_SESS_KEY_SIZE + CIFS_CPHTXT_SIZE + 2;
+
+	if (ses->domainName)
+		sz += 2 * strnlen(ses->domainName, CIFS_MAX_DOMAINNAME_LEN);
+	else
+		sz += 2;
+
+	if (ses->user_name)
+		sz += 2 * strnlen(ses->user_name, MAX_USERNAME_SIZE);
+	else
+		sz += 2;
+
+	return sz;
+}
+
+static int build_ntlmssp_auth_blob(unsigned char **pbuffer,
 					u16 *buflen,
 				   struct cifs_ses *ses,
 				   const struct nls_table *nls_cp)
 {
 	int rc;
-	AUTHENTICATE_MESSAGE *sec_blob = (AUTHENTICATE_MESSAGE *)pbuffer;
+	AUTHENTICATE_MESSAGE *sec_blob;
 	__u32 flags;
 	unsigned char *tmp;
 
+	rc = setup_ntlmv2_rsp(ses, nls_cp);
+	if (rc) {
+		cERROR(1, "Error %d during NTLMSSP authentication", rc);
+		*buflen = 0;
+		goto setup_ntlmv2_ret;
+	}
+	*pbuffer = kmalloc(size_of_ntlmssp_blob(ses), GFP_KERNEL);
+	sec_blob = (AUTHENTICATE_MESSAGE *)*pbuffer;
+
 	memcpy(sec_blob->Signature, NTLMSSP_SIGNATURE, 8);
 	sec_blob->MessageType = NtLmAuthenticate;
 
@@ -471,7 +495,7 @@ static int build_ntlmssp_auth_blob(unsigned char *pbuffer,
 			flags |= NTLMSSP_NEGOTIATE_KEY_XCH;
 	}
 
-	tmp = pbuffer + sizeof(AUTHENTICATE_MESSAGE);
+	tmp = *pbuffer + sizeof(AUTHENTICATE_MESSAGE);
 	sec_blob->NegotiateFlags = cpu_to_le32(flags);
 
 	sec_blob->LmChallengeResponse.BufferOffset =
@@ -479,13 +503,9 @@ static int build_ntlmssp_auth_blob(unsigned char *pbuffer,
 	sec_blob->LmChallengeResponse.Length = 0;
 	sec_blob->LmChallengeResponse.MaximumLength = 0;
 
-	sec_blob->NtChallengeResponse.BufferOffset = cpu_to_le32(tmp - pbuffer);
+	sec_blob->NtChallengeResponse.BufferOffset =
+				cpu_to_le32(tmp - *pbuffer);
 	if (ses->user_name != NULL) {
-		rc = setup_ntlmv2_rsp(ses, nls_cp);
-		if (rc) {
-			cERROR(1, "Error %d during NTLMSSP authentication", rc);
-			goto setup_ntlmv2_ret;
-		}
 		memcpy(tmp, ses->auth_key.response + CIFS_SESS_KEY_SIZE,
 				ses->auth_key.len - CIFS_SESS_KEY_SIZE);
 		tmp += ses->auth_key.len - CIFS_SESS_KEY_SIZE;
@@ -503,7 +523,7 @@ static int build_ntlmssp_auth_blob(unsigned char *pbuffer,
 	}
 
 	if (ses->domainName == NULL) {
-		sec_blob->DomainName.BufferOffset = cpu_to_le32(tmp - pbuffer);
+		sec_blob->DomainName.BufferOffset = cpu_to_le32(tmp - *pbuffer);
 		sec_blob->DomainName.Length = 0;
 		sec_blob->DomainName.MaximumLength = 0;
 		tmp += 2;
@@ -512,14 +532,14 @@ static int build_ntlmssp_auth_blob(unsigned char *pbuffer,
 		len = cifs_strtoUCS((__le16 *)tmp, ses->domainName,
 				    MAX_USERNAME_SIZE, nls_cp);
 		len *= 2; /* unicode is 2 bytes each */
-		sec_blob->DomainName.BufferOffset = cpu_to_le32(tmp - pbuffer);
+		sec_blob->DomainName.BufferOffset = cpu_to_le32(tmp - *pbuffer);
 		sec_blob->DomainName.Length = cpu_to_le16(len);
 		sec_blob->DomainName.MaximumLength = cpu_to_le16(len);
 		tmp += len;
 	}
 
 	if (ses->user_name == NULL) {
-		sec_blob->UserName.BufferOffset = cpu_to_le32(tmp - pbuffer);
+		sec_blob->UserName.BufferOffset = cpu_to_le32(tmp - *pbuffer);
 		sec_blob->UserName.Length = 0;
 		sec_blob->UserName.MaximumLength = 0;
 		tmp += 2;
@@ -528,13 +548,13 @@ static int build_ntlmssp_auth_blob(unsigned char *pbuffer,
 		len = cifs_strtoUCS((__le16 *)tmp, ses->user_name,
 				    MAX_USERNAME_SIZE, nls_cp);
 		len *= 2; /* unicode is 2 bytes each */
-		sec_blob->UserName.BufferOffset = cpu_to_le32(tmp - pbuffer);
+		sec_blob->UserName.BufferOffset = cpu_to_le32(tmp - *pbuffer);
 		sec_blob->UserName.Length = cpu_to_le16(len);
 		sec_blob->UserName.MaximumLength = cpu_to_le16(len);
 		tmp += len;
 	}
 
-	sec_blob->WorkstationName.BufferOffset = cpu_to_le32(tmp - pbuffer);
+	sec_blob->WorkstationName.BufferOffset = cpu_to_le32(tmp - *pbuffer);
 	sec_blob->WorkstationName.Length = 0;
 	sec_blob->WorkstationName.MaximumLength = 0;
 	tmp += 2;
@@ -543,19 +563,19 @@ static int build_ntlmssp_auth_blob(unsigned char *pbuffer,
 		(ses->ntlmssp->server_flags & NTLMSSP_NEGOTIATE_EXTENDED_SEC))
 			&& !calc_seckey(ses)) {
 		memcpy(tmp, ses->ntlmssp->ciphertext, CIFS_CPHTXT_SIZE);
-		sec_blob->SessionKey.BufferOffset = cpu_to_le32(tmp - pbuffer);
+		sec_blob->SessionKey.BufferOffset = cpu_to_le32(tmp - *pbuffer);
 		sec_blob->SessionKey.Length = cpu_to_le16(CIFS_CPHTXT_SIZE);
 		sec_blob->SessionKey.MaximumLength =
 				cpu_to_le16(CIFS_CPHTXT_SIZE);
 		tmp += CIFS_CPHTXT_SIZE;
 	} else {
-		sec_blob->SessionKey.BufferOffset = cpu_to_le32(tmp - pbuffer);
+		sec_blob->SessionKey.BufferOffset = cpu_to_le32(tmp - *pbuffer);
 		sec_blob->SessionKey.Length = 0;
 		sec_blob->SessionKey.MaximumLength = 0;
 	}
 
+	*buflen = tmp - *pbuffer;
 setup_ntlmv2_ret:
-	*buflen = tmp - pbuffer;
 	return rc;
 }
 
@@ -578,7 +598,7 @@ CIFS_SessSetup(unsigned int xid, struct cifs_ses *ses,
 	struct key *spnego_key = NULL;
 	__le32 phase = NtLmNegotiate; /* NTLMSSP, if needed, is multistage */
 	u16 blob_len;
-	char *ntlmsspblob = NULL;
+	unsigned char *ntlmsspblob = NULL;
 
 	if (ses == NULL)
 		return -EINVAL;
@@ -832,21 +852,7 @@ CIFS_SessSetup(unsigned int xid, struct cifs_ses *ses,
 				cpu_to_le16(sizeof(NEGOTIATE_MESSAGE));
 			break;
 		case NtLmAuthenticate:
-			/*
-			 * 5 is an empirical value, large enough to hold
-			 * authenticate message plus max 10 of av paris,
-			 * domain, user, workstation names, flags, etc.
-			 */
-			ntlmsspblob = kzalloc(
-				5*sizeof(struct _AUTHENTICATE_MESSAGE),
-				GFP_KERNEL);
-			if (!ntlmsspblob) {
-				cERROR(1, "Can't allocate NTLMSSP blob");
-				rc = -ENOMEM;
-				goto ssetup_exit;
-			}
-
-			rc = build_ntlmssp_auth_blob(ntlmsspblob,
+			rc = build_ntlmssp_auth_blob(&ntlmsspblob,
 						&blob_len, ses, nls_cp);
 			if (rc)
 				goto ssetup_exit;