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plugins/libplugin-pay.c: Keep p->invoice->routes valid when the routehints paymod mutates it.

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The routehints paymod shares the storage of the array d->routehints and
p->invoice->routes, but once it operates, it possibly leaves it as a stale
pointer to memory it used to have.

Since other paymods may be interested in the invoice details, including
the routehints in the invoice, we should ensure the p->invoice->routes
remains valid whenever we try mutating that array.
This commit is contained in:
ZmnSCPxj jxPCSnmZ 2020-08-14 00:36:17 +08:00 committed by Rusty Russell
parent 2d86014e53
commit d15717b576
1 changed files with 35 additions and 1 deletions
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36
plugins/libplugin-pay.c
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@ -2206,8 +2206,21 @@ static struct command_result *routehint_getroute_result(struct command *cmd,
* routehints. */
d->destination_reachable = (rtok != NULL);
if (d->destination_reachable)
if (d->destination_reachable) {
tal_arr_expand(&d->routehints, NULL);
/* The above could trigger a realloc.
* However, p->invoice->routes and d->routehints are
* actually the same array, so we need to update the
* p->invoice->routes pointer, since the realloc
* might have changed pointer addresses, in order to
* ensure that the pointers are not stale.
*/
p->invoice->routes = d->routehints;
/* FIXME: ***DO*** we need to add this extra routehint?
* Once we run out of routehints the default system will
* just attempt directly routing to the destination anyway. */
}
routehint_pre_getroute(d, p);
@ -2260,6 +2273,27 @@ static void routehint_step_cb(struct routehints_data *d, struct payment *p)
if (p->parent == NULL) {
d->routehints = filter_routehints(d, p->local_id,
p->invoice->routes);
/* filter_routehints modifies the array, but
* this could trigger a resize and the resize
* could trigger a realloc.
* Keep the invoice pointer up-to-date.
* FIXME: We should really consider that if we are
* mutating p->invoices->routes, maybe we should
* drop d->routehints and just use p->invoice->routes
* directly.
* It is probably not a good idea to *copy* the
* routehints: other paymods are interested in
* p->invoice->routes, and if the routehints system
* itself adds or removes routehints from its
* copy, the *actual* number of routehints that we
* end up using is the one that the routehints paymod
* is maintaining and traversing, and it is *that*
* set of routehints that is the important one.
* So rather than copying the array of routehints
* in paymod, paymod should use (and mutate) the
* p->invoice->routes array, and
*/
p->invoice->routes = d->routehints;
paymod_log(p, LOG_DBG,
"After filtering routehints we're left with "