ctdb: stack leakage over wire

[Stefan (metze) Metzmacher]

Rusty Russell schrieb:
> Hi all,
> 
>    Running valgrind showed that we're leaking uninitialized vars over the
> wire.  In particular on 64 bit x86:
> 
> 	struct takeover_run_reply {
> 		uint32_t pnn;
> 		uint64_t srvid;
> 	};
> 
> The padding bytes between the two are uninitialized:
> 
> 	static void ctdb_health_callback(struct ctdb_context *ctdb, int status, void *p)
> 	{
> 	...
> 		struct takeover_run_reply rd;
> 	...
> 		rd.pnn   = ctdb->pnn;
> 		rd.srvid = CTDB_SRVID_TAKEOVER_RUN_RESPONSE;
> 
> This then gets memcpy'd by generic routines into the packet.  Fixing this case
> is easy, but there are others.  There are several solutions I can see:
> 
> 1) Try to remember to explicitly set stuff everywhere (whack-a-mole),
> 2) Explicit marshal/unmarshall funcs for each type (slightly less fragile, as
>    only those funcs need to remember to zero),
> 3) Set attribute((packed)) (breaks wire format, assumes gcc extension),
> 4) Bite the bullet and marshall/unmarshall into a portable format (breaks
>    wire format, but allows potential for cross-platform ctdb).

I would prefer 4), but it has a lot of impact on the current code layout
and maybe also impact performance...

metze

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