cifs: Use data structures to compute NTLMv2 response offsets

A bit of cleanup plus some gratuitous variable renaming. I think using
structures instead of numeric offsets makes this code much more
understandable.

Also added a comment about current time range expected by
the server.
Acked-by: Jeff Layton <jlayton@redhat.com>
Reviewed-by: Shirish Pargaonkar <spargaonkar@suse.com>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>
Signed-off-by: Steve French <smfrench@gmail.com>

fs/cifs/cifsencrypt.c

@@ -548,7 +548,13 @@ static int
 CalcNTLMv2_response(const struct cifs_ses *ses, char *ntlmv2_hash)
 {
 	int rc;
-	unsigned int offset = CIFS_SESS_KEY_SIZE + 8;
+	struct ntlmv2_resp *ntlmv2 = (struct ntlmv2_resp *)
+	    (ses->auth_key.response + CIFS_SESS_KEY_SIZE);
+	unsigned int hash_len;
+
+	/* The MD5 hash starts at challenge_key.key */
+	hash_len = ses->auth_key.len - (CIFS_SESS_KEY_SIZE +
+		offsetof(struct ntlmv2_resp, challenge.key[0]));
 
 	if (!ses->server->secmech.sdeschmacmd5) {
 		cifs_dbg(VFS, "%s: can't generate ntlmv2 hash\n", __func__);
@@ -570,20 +576,21 @@ CalcNTLMv2_response(const struct cifs_ses *ses, char *ntlmv2_hash)
 	}
 
 	if (ses->server->negflavor == CIFS_NEGFLAVOR_EXTENDED)
-		memcpy(ses->auth_key.response + offset,
+		memcpy(ntlmv2->challenge.key,
 		       ses->ntlmssp->cryptkey, CIFS_SERVER_CHALLENGE_SIZE);
 	else
-		memcpy(ses->auth_key.response + offset,
+		memcpy(ntlmv2->challenge.key,
 		       ses->server->cryptkey, CIFS_SERVER_CHALLENGE_SIZE);
 	rc = crypto_shash_update(&ses->server->secmech.sdeschmacmd5->shash,
-		ses->auth_key.response + offset, ses->auth_key.len - offset);
+				 ntlmv2->challenge.key, hash_len);
 	if (rc) {
 		cifs_dbg(VFS, "%s: Could not update with response\n", __func__);
 		return rc;
 	}
 
+	/* Note that the MD5 digest over writes anon.challenge_key.key */
 	rc = crypto_shash_final(&ses->server->secmech.sdeschmacmd5->shash,
-		ses->auth_key.response + CIFS_SESS_KEY_SIZE);
+				ntlmv2->ntlmv2_hash);
 	if (rc)
 		cifs_dbg(VFS, "%s: Could not generate md5 hash\n", __func__);
 
@@ -627,7 +634,7 @@ setup_ntlmv2_rsp(struct cifs_ses *ses, const struct nls_table *nls_cp)
 	int rc;
 	int baselen;
 	unsigned int tilen;
-	struct ntlmv2_resp *buf;
+	struct ntlmv2_resp *ntlmv2;
 	char ntlmv2_hash[16];
 	unsigned char *tiblob = NULL; /* target info blob */
 
@@ -660,13 +667,14 @@ setup_ntlmv2_rsp(struct cifs_ses *ses, const struct nls_table *nls_cp)
 	}
 	ses->auth_key.len += baselen;
 
-	buf = (struct ntlmv2_resp *)
+	ntlmv2 = (struct ntlmv2_resp *)
 			(ses->auth_key.response + CIFS_SESS_KEY_SIZE);
-	buf->blob_signature = cpu_to_le32(0x00000101);
-	buf->reserved = 0;
-	buf->time = cpu_to_le64(cifs_UnixTimeToNT(CURRENT_TIME));
-	get_random_bytes(&buf->client_chal, sizeof(buf->client_chal));
-	buf->reserved2 = 0;
+	ntlmv2->blob_signature = cpu_to_le32(0x00000101);
+	ntlmv2->reserved = 0;
+	/* Must be within 5 minutes of the server */
+	ntlmv2->time = cpu_to_le64(cifs_UnixTimeToNT(CURRENT_TIME));
+	get_random_bytes(&ntlmv2->client_chal, sizeof(ntlmv2->client_chal));
+	ntlmv2->reserved2 = 0;
 
 	memcpy(ses->auth_key.response + baselen, tiblob, tilen);
 
@@ -706,7 +714,7 @@ setup_ntlmv2_rsp(struct cifs_ses *ses, const struct nls_table *nls_cp)
 	}
 
 	rc = crypto_shash_update(&ses->server->secmech.sdeschmacmd5->shash,
-		ses->auth_key.response + CIFS_SESS_KEY_SIZE,
+		ntlmv2->ntlmv2_hash,
 		CIFS_HMAC_MD5_HASH_SIZE);
 	if (rc) {
 		cifs_dbg(VFS, "%s: Could not update with response\n", __func__);

fs/cifs/cifspdu.h

@@ -697,7 +697,13 @@ struct ntlmssp2_name {
 } __attribute__((packed));
 
 struct ntlmv2_resp {
+	union {
 	    char ntlmv2_hash[CIFS_ENCPWD_SIZE];
+	    struct {
+		__u8 reserved[8];
+		__u8 key[CIFS_SERVER_CHALLENGE_SIZE];
+	    } __attribute__((packed)) challenge;
+	} __attribute__((packed));
 	__le32 blob_signature;
 	__u32  reserved;
 	__le64  time;