[CIFS] Maximum username length check in session setup does not match

Fix length check reported by D. Binderman (see below)

d binderman <dcb314@hotmail.com> wrote:
>
> I just ran the sourceforge tool cppcheck over the source code of the
> new Linux kernel 2.6.33-rc6
>
> It said
>
> [./cifs/sess.c:250]: (error) Buffer access out-of-bounds

May turn out to be harmless, but best to be safe. Note max
username length is defined to 32 due to Linux (Windows
maximum is 20).
Signed-off-by: Steve French <sfrench@us.ibm.com>

fs/cifs/sess.c

@@ -223,9 +223,9 @@ static void unicode_ssetup_strings(char **pbcc_area, struct cifsSesInfo *ses,
 		/* null user mount */
 		*bcc_ptr = 0;
 		*(bcc_ptr+1) = 0;
-	} else { /* 300 should be long enough for any conceivable user name */
+	} else {
 		bytes_ret = cifs_strtoUCS((__le16 *) bcc_ptr, ses->userName,
-					  300, nls_cp);
+					  MAX_USERNAME_SIZE, nls_cp);
 	}
 	bcc_ptr += 2 * bytes_ret;
 	bcc_ptr += 2; /* account for null termination */
@@ -246,11 +246,10 @@ static void ascii_ssetup_strings(char **pbcc_area, struct cifsSesInfo *ses,
 	/* copy user */
 	if (ses->userName == NULL) {
 		/* BB what about null user mounts - check that we do this BB */
-	} else { /* 300 should be long enough for any conceivable user name */
-		strncpy(bcc_ptr, ses->userName, 300);
+	} else {
+		strncpy(bcc_ptr, ses->userName, MAX_USERNAME_SIZE);
 	}
-	/* BB improve check for overflow */
-	bcc_ptr += strnlen(ses->userName, 300);
+	bcc_ptr += strnlen(ses->userName, MAX_USERNAME_SIZE);
 	*bcc_ptr = 0;
 	bcc_ptr++; /* account for null termination */