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lltable: Fix use-after-free race in llentry_free() #2219

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lltable: Fix use-after-free race in llentry_free() #2219

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26 changes: 24 additions & 2 deletions sys/net/if_llatbl.c
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Original file line number Diff line number Diff line change
Expand Up @@ -649,16 +649,38 @@ size_t
llentry_free(struct llentry *lle)
{
size_t pkts_dropped;
int ret;

LLE_WLOCK_ASSERT(lle);

KASSERT((lle->la_flags & LLE_LINKED) == 0, ("freeing linked lle"));

pkts_dropped = lltable_drop_entry_queue(lle);

/* cancel timer */
if (callout_stop(&lle->lle_timer) > 0)
/*
* Cancel timer. Handle races with timer callback.
*/
ret = callout_stop(&lle->lle_timer);
if (ret > 0) {
LLE_REMREF(lle);
} else if (ret == 0) {
/*
* Timer callback is executing. Two cases:
*
* refcnt > 1: Another thread is calling us while the timer
* is running. The entry is already unlinked (KASSERT above),
* so timer will skip its LLE_REMREF. Drop one ref and bail;
* timer's llentry_free() will free the entry.
*
* refcnt == 1: We are the timer callback and already dropped
* our ref before calling llentry_free(). Proceed to free.
*/
if (lle->lle_refcnt > 1) {
LLE_REMREF(lle);
LLE_WUNLOCK(lle);
return (pkts_dropped);
}
}
LLE_FREE_LOCKED(lle);

return (pkts_dropped);
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