[PATCH] debuginfod: PR27917 - protect against federation loops

[Frank Ch. Eigler]

Hi -

> This patch aims to reduce the risk by adding an option to debuginfod
> that functions kind of like an IP packet's TTL: a limit on the
> length of XFF: header that debuginfod is willing to process. If
> X-Forwarded-For: exceeds N hops, it will not delegate a local lookup
> miss to upstream debuginfods. [...]

Thank you very much!


> Commit ab38d167c40c99 causes federation loops for non-existent
> resources to result in multiple temporary livelocks, each lasting
> for $DEBUGINFOD_TIMEOUT seconds. [...]

(FWIW, the term "livelock" is not quite right here, try just
"deadlock".)

The patch looks functional, and thank you also for including the
docs and test case.  Thorough enough!


> @@ -1862,6 +1869,12 @@ handle_buildid (MHD_Connection* conn,
>    // We couldn't find it in the database.  Last ditch effort
>    // is to defer to other debuginfo servers.
> 
> +  // if X-Forwarded-For: exceeds N hops,
> +  // do not delegate a local lookup miss to upstream debuginfods.
> +  if (disable_query_server)
> +    throw reportable_exception(MHD_HTTP_NOT_FOUND, "not found,
> --forwared-ttl-limit reached \
> +and will not query the upstream servers");

One part I don't understand is why you added the code to check for XFF
length into handler_cb(), and then passed the disable_query_server
result flag to this function.  Was there some reason not to perform
the XFF comma-counting right here?


- FChE