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  • Public Facing Recursive DNS Servers - iptables rules

    - by David Schwartz
    We run public-facing recursive DNS servers on Linux machines. We've been used for DNS amplification attacks. Are there any recommended iptables rules that would help mitigate these attacks? The obvious solution is just to limit outbound DNS packets to a certain traffic level. But I was hoping to find something a little bit more clever so that an attack just blocks off traffic to the victim IP address. I've searched for advice and suggestions, but they all seem to be "don't run public-facing recursive name servers". Unfortunately, we are backed into a situation where things that are not easy to change will break if we don't do so, and this is due to decisions made more than a decade ago before these attacks were an issue.

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  • MS SQL server and Trees

    - by Julian
    Im looking for some way of extrating data form a tree table as defined below. Table Tree Defined as :- TreeID uniqueidentifier TreeParent uniqueidentifier TreeCode varchar(50) TreeDesc varchar(100) Data some (23k rows), Parent Refs back into ID in table The following SQL renders the whole tree (takes arround 2 mins 30) I need to do the following. 1) Render each Tree Node with its LVL 1 parent 2) Render all nodes that have a Description that matches a TreeDesc like 'SomeText%' 3) Render all parent nodes that are for a single tree id. Items 2 and 3 take 2mins30 so this needs to be a lot faster! Item 1, just cant work out how to do it with out killing SQL or taking forever any sugestions would be helpfull Thanks Julian WITH TreeCTE(TreeCode, TreeDesc, depth, TreeParent, TreeID) AS ( -- anchor member SELECT cast('' as varchar(50)) as TreeCode , cast('Trees' as varchar(100)) as TreeDesc, cast('0' as Integer) as depth, cast('00000000-0000-0000-0000-000000000000' as uniqueidentifier) as TreeParent, cast('00000000-0000-0000-0000-000000000000' as uniqueidentifier) as TreeID UNION ALL -- recursive member SELECT s.TreeCode, s.TreeDesc, cte.depth+1, isnull(s.TreeParent, cast('00000000-0000-0000-0000-000000000000' as uniqueidentifier)), isnull(s.TreeID, cast('00000000-0000-0000-0000-000000000000' as uniqueidentifier)) FROM pdTrees AS S JOIN TreeCTE AS cte ON isnull(s.TreeParent, cast('00000000-0000-0000-0000-000000000000' as uniqueidentifier)) = isnull( cte.TreeID , cast('00000000-0000-0000-0000-000000000000' as uniqueidentifier)) ) -- outer query SELECT s.TreeID, s.TreeCode, s.TreeDesc, s.depth, s.TreeParent FROM TreeCTE s

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  • CTE and last known date processing

    - by stackoverflowuser
    Input @StartDate = '01/25/2010' @EndDate = '02/06/2010' I have 2 CTEs in a stored procedure as follows: with CTE_A as ( [gives output A..Shown below] ), with CTE_B as ( Here, I want to check if @StartDate is NOT in output A then replace it with the last known date. In this case, since @startdate is less than any date in output A hence @StartDate will become 02/01/2010. Also to check if @EndDate is NOT in output A then replace it with the last known date. In this case, since @enddate is 02/06/2010 hence it will be replace with 02/05/2010. // Here there is a query using @startDate and @EndDate. ) output A Name Date A 02/01/2010 B 02/01/2010 C 02/05/2010 D 02/10/2010

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  • Need help with a SQL CTE Query

    - by Chuck
    I have a table that I need to get some specific data from for a view. Here's the base table structure with some sample data: | UserID | ReportsToUserID | Org ID | ------------------------------------- | 1 | NULL | 1 | ------------------------------------- | 2 | 1 | 1 | ------------------------------------- | 3 | 2 | 1 | ------------------------------------- | 4 | 3 | 1 | ------------------------------------- The users will be entering reports and users can see the reports of users who report to them and any users who report to those users. Users who report to no one can see everything in their organization Given my sample data above, user 1 can see the reports of 2, 3, & 4; user 2 can see the reports of 3 & 4; and user 3 can see the reports of 4. For the view, I'd like to have the data returned as follows: | UserID | CanSeeUserID | OrgID | -------------------------------------------- | 1 | 2 | 1 | -------------------------------------------- | 1 | 3 | 1 | -------------------------------------------- | 1 | 4 | 1 | -------------------------------------------- | 2 | 3 | 1 | -------------------------------------------- etc... Below is my current code, any help is greatly appreciated. WITH CTEUsers (UserID, CanSeeUserID, OrgID) AS ( SELECT e.ID, e.ReportsToUserID, e.OrgID FROM Users e WITH(NOLOCK) WHERE COALESCE(ReportsToUserID,0) = 0 --ReportsToUserID can be NULL or 0 UNION ALL SELECT e.ReportsToUserID, e.ID,e.OrgID FROM Users e WITH(NOLOCK) JOIN CTEUsers c ON e.ID = c.UserID ) SELECT * FROM CTEUsers

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  • Can a destructor be recursive?

    - by Cubbi
    Is this program well-defined, and if not, why exactly? #include <iostream> #include <new> struct X { int cnt; X (int i) : cnt(i) {} ~X() { std::cout << "destructor called, cnt=" << cnt << std::endl; if ( cnt-- > 0 ) this->X::~X(); // explicit recursive call to dtor } }; int main() { char* buf = new char[sizeof(X)]; X* p = new(buf) X(7); p->X::~X(); // explicit call to dtor delete[] buf; } My reasoning: although invoking a destructor twice is undefined behavior, per 12.4/14, what it says exactly is this: the behavior is undefined if the destructor is invoked for an object whose lifetime has ended Which does not seem to prohibit recursive calls. While the destructor for an object is executing, the object's lifetime has not yet ended, thus it's not UB to invoke the destructor again. On the other hand, 12.4/6 says: After executing the body [...] a destructor for class X calls the destructors for X's direct members, the destructors for X's direct base classes [...] which means that after the return from a recursive invocation of a destructor, all member and base class destructors will have been called, and calling them again when returning to the previous level of recursion would be UB. Therefore, a class with no base and only POD members can have a recursive destructor without UB. Am I right?

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  • Java iterative vs recursive

    - by user1389813
    Can anyone explain why the following recursive method is faster than the iterative one (Both are doing it string concatenation) ? Isn't the iterative approach suppose to beat up the recursive one ? plus each recursive call adds a new layer on top of the stack which can be very space inefficient. private static void string_concat(StringBuilder sb, int count){ if(count >= 9999) return; string_concat(sb.append(count), count+1); } public static void main(String [] arg){ long s = System.currentTimeMillis(); StringBuilder sb = new StringBuilder(); for(int i = 0; i < 9999; i++){ sb.append(i); } System.out.println(System.currentTimeMillis()-s); s = System.currentTimeMillis(); string_concat(new StringBuilder(),0); System.out.println(System.currentTimeMillis()-s); } I ran the program multiple time, and the recursive one always ends up 3-4 times faster than the iterative one. What could be the main reason there that is causing the iterative one slower ?

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  • What does this code do? Recursive Iterator in php?

    - by Ali
    I'm working on a zend framework based email project and I'm following some code samples online.. I can't understand this line of code which apparently loops through different 'parts' of an email message. I have no idea how it works btw and suspect that theres some error taking place which my parser isn't showing right. foreach (new RecursiveIteratorIterator($mail->getMessage($i)) as $ii=>$part) what does the above foreach loop mean?

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  • Recursive Syntax in Oslo

    - by Kevin Lawrence
    I'm writing my first DSL with Oslo and I am having a problem with a recursive syntax definition. The input has sections which can contain questions or other sections recursively (composite pattern) like this: Section: A Question: 1 Question: 2 Section: B Question: 1 End End My definition for a Section looks like this syntax Section = "Section:" id:Text body:(SectionBody)* "End Section"; Which works (but doesn't handle recursive sections) if I define SectionBody like this syntax SectionBody = (Question); but doesn't work with a recursive definition like this syntax SectionBody = (Question | Section); What am I missing?

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  • wget recursive limited within subdomain

    - by Paul Seangwongree
    I want to download the following subdomain with the recursive option using wget: www.example.com/A/B So if that URL has links to www.example.com/A/B/C and www.example.com/A/B/D, these two should also be downloaded. But I don't want anything outside the www.example.com/A/B subdomain to be downloaded. For example, if www.example.com/A/B/C has a link back to www.example.com, the page www.example.com should not be downloaded. What wget command should I use?

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  • Correct way to model recursive relationship in Django

    - by Yuval A
    My application has two node types: a parent node which can hold recursive child nodes. Think of it like the post-comment system in SO, but comments can be recursive: parent_1 child_11 child_12 child_121 child_3 parent_2 child_21 child_211 child_2111 Important to note that the parent nodes have different attributes and behavior than the child nodes. What is the correct (and presumably most efficient) way of modeling this relationship in Django?

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  • Recognizing Tail-recursive functions with Flex+Bison and convert code to an Iterative form

    - by Viet
    I'm writing a calculator with an ability to accept new function definitions. Being aware of the need of newbies to try recursive functions such as Fibonacci, I would like my calculator to be able to recognize Tail-recursive functions with Flex + Bison and convert code to an Iterative form. I'm using Flex & Bison to do the job. If you have any hints or ideas, I welcome them warmly. Thanks!

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  • How to work with CTE. There is some error related to anchor.

    - by Shantanu Gupta
    I am creating a hierarchy representaion of a column. But an error occurs Details are Msg 240, Level 16, State 1, Line 1 Types don't match between the anchor and the recursive part in column "DISPLAY" of recursive query "CTE". I know there is some typecasting error. But I dont know how to remove error. Please just dont only sort out my error. I need explanation why this error is coming. When this error occurs. I am trying to sort table on the basis of sort col that i m introducing. I want to add '-' at every level and want to sort accordingly. Please help WITH CTE (PK_CATEGORY_ID, [DESCRIPTION], FK_CATEGORY_ID, DISPLAY, SORT, DEPTH) AS ( SELECT PK_CATEGORY_ID, [DESCRIPTION], FK_CATEGORY_ID, '-' AS DISPLAY, '--' AS SORT, 0 AS DEPTH FROM dbo.L_CATEGORY_TYPE WHERE FK_CATEGORY_ID IS NULL UNION ALL SELECT T.PK_CATEGORY_ID, T.[DESCRIPTION], T.FK_CATEGORY_ID, CAST(DISPLAY+T.[DESCRIPTION] AS VARCHAR(1000)), '--' AS SORT, C.DEPTH +1 FROM dbo.L_CATEGORY_TYPE T JOIN CTE C ON C.PK_CATEGORY_ID = T.FK_CATEGORY_ID --SELECT T.PK_CATEGORY_ID, C.SORT+T.[DESCRIPTION], T.FK_CATEGORY_ID --, CAST('--' + C.SORT AS VARCHAR(1000)) AS SORT, CAST(DEPTH +1 AS INT) AS DEPTH --FROM dbo.L_CATEGORY_TYPE T JOIN CTE C ON C.FK_CATEGORY_ID = T.PK_CATEGORY_ID ) SELECT PK_CATEGORY_ID, [DESCRIPTION], FK_CATEGORY_ID, DISPLAY, SORT, DEPTH FROM CTE ORDER BY SORT

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  • Recursive insert-method for a linked list

    - by user3726477
    I'm learning C# and I've made a recursive insert-method for a linked list: public static int recursiveInsert(ref int value, ref MyLinkedList list) { if (list == null) return new MyLinkedList(value, null); else { list.next = recursiveInsert(ref int value, ref list.next); return list; } } How would you modify this method to make the recursive call look like this: recursiveInsert(value, ref list.next) instead of: list.next = recursiveInsert(ref int value, ref list.next);

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  • Scala: recursive search avoiding cycles

    - by user1826663
    How can I write a recursive search that I avoid cycles. My class is this: class Component(var name: String, var number: Int, var subComponent: Set[Component]) Now I need a way to check whether a component is contained within its subcomponent or between subcomponent of its subcomponent and so on.Avoiding possible cycles caused by other Component. My method of recursive search must have the following signature, where subC is the Set [component] of comp. def content (comp: Component, subC: Set[Component]) : Boolean = { } Thanks for the help.

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  • Simple recursive DNS resolver for debugging (app or VM)

    - by notpeter
    I have an issue which I believe is caused by incorrect DNS queries (doubled subdomains like _record.host.subdomain.tld.subdomain.tld) when querying for SRV records. So I need to an alternate DNS server with heavy logging so I can see every query (especially stupid ones), acting as a recursive resolver with the ability create records which override real DNS records so I can not only find the records it's (wrongly) looking for, but populate those records as well. I know I could install a DNS server on yet another linux box, but I feel like this is the sort of thing that someone may already setup a simple python script or single use vm just for this purpose.

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  • Tail-recursive merge sort in OCaml

    - by CFP
    Hello world! I’m trying to implement a tail-recursive list-sorting function in OCaml, and I’ve come up with the following code: let tailrec_merge_sort l = let split l = let rec _split source left right = match source with | [] -> (left, right) | head :: tail -> _split tail right (head :: left) in _split l [] [] in let merge l1 l2 = let rec _merge l1 l2 result = match l1, l2 with | [], [] -> result | [], h :: t | h :: t, [] -> _merge [] t (h :: result) | h1 :: t1, h2 :: t2 -> if h1 < h2 then _merge t1 l2 (h1 :: result) else _merge l1 t2 (h2 :: result) in List.rev (_merge l1 l2 []) in let rec sort = function | [] -> [] | [a] -> [a] | list -> let left, right = split list in merge (sort left) (sort right) in sort l ;; Yet it seems that it is not actually tail-recursive, since I encounter a "Stack overflow during evaluation (looping recursion?)" error. Could you please help me spot the non tail-recursive call in this code? I've searched quite a lot, without finding it. Cout it be the let binding in the sort function? Thanks a lot, CFP.

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  • A F# tail-recursive question

    - by ksharp
    Recently, I'm learning F#. I try to solve problem in different ways. Like this: (* [0;1;2;3;4;5;6;7;8] -> [(0,1,2);(3,4,5);(6,7,8)] *) //head-recursive let rec toTriplet_v1 list= match list with | a::b::c::t -> (a,b,c)::(toTriplet_v1 t) | _ -> [] //tail-recursive let toTriplet_v2 list= let rec loop lst acc= match lst with | a::b::c::t -> loop t ((a,b,c)::acc) | _ -> acc loop list [] //tail-recursive(???) let toTriplet_v3 list= let rec loop lst accfun= match lst with | a::b::c::t -> loop t (fun ls -> accfun ((a,b,c)::ls)) | _ -> accfun [] loop list (fun x -> x) let funs = [toTriplet_v1; toTriplet_v2; toTriplet_v3]; funs |> List.map (fun x -> x [0..8]) |> List.iteri (fun i x -> printfn "V%d : %A" (i+1) x) I thought the results of V2 and V3 should be the same. But, I get the result below: V1 : [(0, 1, 2); (3, 4, 5); (6, 7, 8)] V2 : [(6, 7, 8); (3, 4, 5); (0, 1, 2)] V3 : [(0, 1, 2); (3, 4, 5); (6, 7, 8)] Why the results of V2 and V3 are different?

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  • recursive grep started at / hangs

    - by Martin
    I have used following grep search pattern on multiple platforms: grep -r -I -D skip 'string_to_match' / For example on FreeBSD 8.0, FreeBSD 6.4 and Debian 6.0(squeeze). Command does a recursive search starting from root directory, assumes that binary files do not have the 'string_to_match' and skips devices, sockets and named pipes. FreeBSD 8.0 and FreeBSD 6.4 use GNU grep version 2.5.1 and Debian 6.0 uses GNU grep version 2.6.3. On FreeBSD 6.4, last information printed to stderr was "grep: /dev/cuad0: Device busy". After this grep just idles as according to "top -m io -o total" the I/O usage of grep is nonexistent. Same behavior is true under FreeBSD 8.0, but last information sent to stderr is "grep: /tmp/.wine-0: Permission denied" on my installation. In case of Debian, last output to stderr is "grep: /proc/sysrq-trigger: Input/output error". If I check the I/O usage of grep process under Debian, it is following: root@Debian:~# iotop -bp 22439 Total DISK READ: 0.00 B/s | Total DISK WRITE: 0.00 B/s TID PRIO USER DISK READ DISK WRITE SWAPIN IO COMMAND 22439 be/4 root 0.00 B/s 0.00 B/s 0.00 % 0.00 % grep -r -I -D skip 10.10.10.99 / Total DISK READ: 0.00 B/s | Total DISK WRITE: 0.00 B/s TID PRIO USER DISK READ DISK WRITE SWAPIN IO COMMAND 22439 be/4 root 0.00 B/s 0.00 B/s 0.00 % 0.00 % grep -r -I -D skip 10.10.10.99 / Total DISK READ: 0.00 B/s | Total DISK WRITE: 0.00 B/s TID PRIO USER DISK READ DISK WRITE SWAPIN IO COMMAND 22439 be/4 root 0.00 B/s 0.00 B/s 0.00 % 0.00 % grep -r -I -D skip 10.10.10.99 / ^Croot@Debian:~# What might cause this? Is there a way to view which file grep is currently processing in case lsof is not present? I'm able to use lsof under Debian and looks like the problematic file name there is "0xc6b2c230 file struct, ty=0, op=0xc0d34120". I'm not sure what this is.. I'm not able to use lsof or fstat under FreeBSD. PS: I know I could use find utility, but this is not the question.

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  • Cannot make bind9 forward DNS query to subdomain unless recursive enabled

    - by PP.
    I am trying to develop my own dynamic DNS. I'm running my own custom DNS for the subdomain on port 5353. ASCII diagram: INET --->:53 Bind 9 --->:5353 node.js | V zone_files I have example.com. The node.js DNS is for dyn.example.com. In my /etc/bind/named.conf.local I have: zone "example.com" { type master; file "/etc/bind/db.com.example"; allow-transfer { zonetxfrsafe; }; }; zone "dyn.example.com" IN { # DYNAMIC type forward; forwarders { 127.0.0.1 port 5353; }; forward only; }; I've even gone so far as to add a NS in my example.com zone file: $TTL 86400 @ IN SOA ns.example.com. hostmaster.example.com. ( 2013070104 ; Serial 7200 ; Refresh 1200 ; Retry 2419200 ; Expire 86400 ) ; Negative Cache TTL ; NS ns ; inet of our nameserver ns A 1.2.3.4 ; NS record for subdomain dyn NS ns When I attempt to get a record from the subdomain server it doesn't get forwarded: dig @127.0.0.1 test.dyn.example.com However if I turn recursive on in /etc/bind/named.conf.options: options { recursion yes; } .. then I CAN see the request going to the subdomain server. But I don't want recursion yes; in my Bind configuration as it is poor security practice (and allows all-and-sundry requests that are not related to my managed zones). How does one forward (proxy) zone queries for just one zone? Or do I give up on Bind altogether and find a DNS server that can actually forward specific queries?

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  • named responding recursive on norecurse queries

    - by Keks
    I have a server on which named is running. It is intercepted with another named server which it is not aware of. Querying the first named server results in timeouts. The server tries to resolve the query recursively. During that the firewall redirects the DNS Request from the first named server to the second one (the query from the first one is addressed to a e.g. a root server and has its "Recursion desired" bit set to 0). Despite that the second named responds to this request with a entirely or at least 1 level more resolved response than the first named server expects. So it ends up with a timeout even though it got a correct name server or even the full IP for the queried domain. In the first case the first name server tries to follow the authority domain ignoring the coresponding glue record and ends up in a loop it aborts: queried: google.com -> got from named#2: ns1.google.com -> ignore glue record and query: ns1.google.com -> got authority from named#2: google.com In the second case it ignores the answer section with the correct IP and instead tries to follow the name servers from the authority section, which ends up in the same dead end as case 1. So how can it be that the second named responds with recursive results even though the bit was explicitly set to 0 in the request from the first named?

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  • Why so much stack space used for each recursion?

    - by Harvey
    I have a simple recursive function RCompare() that calls a more complex function Compare() which returns before the recursive call. Each recursion level uses 248 bytes of stack space which seems like way more than it should. Here is the recursive function: void CMList::RCompare(MP n1) // RECURSIVE and Looping compare function { auto MP ne=n1->mf; while(StkAvl() && Compare(n1=ne->mb)) RCompare(n1); // Recursive call ! } StkAvl() is a simple stack space check function that compares the address of an auto variable to the value of an address near the end of the stack stored in a static variable. It seems to me that the only things added to the stack in each recursion are two pointer variables (MP is a pointer to a structure) and the stuff that one function call stores, a few saved registers, base pointer, return address, etc., all 32-bit (4 byte) values. There's no way that is 248 bytes is it? I don't no how to actually look at the stack in a meaningful way in Visual Studio 2008. Thanks

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